s A Field Guide to the British Seaweeds - NMBAQC

A Field Guide to the British Seaweeds 

As required for assistance in the classification of water 

bodies under the Water Framework Directive

A Field Guide to the British Seaweed 

By Emma Wells 

Wells Marine Surveys 

Introduction 2 

Seaweed collecting and shore searching 3 

Preparation and identification of specimens 10 

Key to seaweed species 19 

Summarised key to species 30 

Summary of species characteristics 39 

Species descriptions and images 46 

Reduced species list identification guide as required by the Water Framework Directive. 1

INTRODUCTION 

The EU Water Framework Directive (WFD) requires water bodies to be classified by 

their chemical and ecological status. Macroalgae are one of the biological quality 

elements to be used in defining the ecological status of a transitional or coastal water 

body. For this particular macroalgae component the directive states that for reference 

conditions the taxonomic composition should correspond totally or nearly totally with 

undisturbed conditions with all sensitive taxa present. As species richness remains 

broadly constant in the absence of environmental alteration this was proposed as an ideal 

measure of quality. Therefore, levels of macroalgae species richness would be used to set 

an ecological quality standard from which any deviation may be measured and used to 

classify water bodies as high, good, moderate and poor. 

However, the identification of intertidal seaweed species requires high levels of 

taxonomic expertise. Therefore, a tool is being developed that may be used by less 

experienced persons to assist with the classification of water bodies. This tool utilises an 

alternative means of recording qualitative species data, which is to implement the use of 

a reduced species list (RSL) whereby the number of species from the RSL will be in 

proportion to total species richness thereby acting as a surrogate. The list is composed of 

species (approximately 70) that are most frequently present on a variety of rocky shores 

within a set geographical area. Additional measurements have been incorporated using 

the RSL including the proportion of green, red and opportunist species and an Ecological 

Status Group ratio. The tool also utilises basic shore descriptions to allow for natural 

variations to be considered. 

The tool aims to fulfil the requirements of the WFD by enabling less experience algal 

taxonomist to classify areas of coastline. This guide aims to assist with such a process by 

providing detailed descriptions on shore sampling methodologies, examples of key 

characteristic from which to identify, a comprehensive yet straight forward algal key and 

detailed images on each species within the RSL. 

Reduced species list identification guide as required by the Water Framework Directive. 

2

SEAWEED COLLECTIONS AND SHORE SEARCHING 

There are general patterns of zonation that occur within the intertidal so to find all 

possible seaweed species the shore needs to be searched thoroughly. This includes 

covering all possible habitats and the full extent of the shore from the upper most 

reaches bordering the terrestrial environment down to the lower reaches only exposed 

during low spring tides. Full algal surveys should include not only those species 

attached directly to the rock surface but also those algae growing in/on other host 

algal species and animals such as hydroids and dead shells: 

• Only attached species to be collected (drift may be from elsewhere although may 

be worth noting presence of some alien species such as Sargassum muticum) 

• Full range of subhabitat types to be sampled: 

- Rockpools, crevices, couloirs (or large crevices), ledges, overhangs 

and caves 

- Upper shore rocks and freshwater seepage for Chlorophyta mats 

- Under canopy algae for small, fine filamentous forms 

Reduced species list identification guide as required by the Water Framework Directive 3

- Turfs of mixed species including a variety of morphological forms 

• Epiphytes – algae growing on other host algal species – for example: 

- Elachista sp. and Ulothrix sp. on Fucus 

- Litosiphon sp. on Alaria and Chorda. 

- Encrusting Corallines on Polyides 

- Many small epiphytes on various filamentous species such 

as Cladophora 

- Red epiphytes on kelp stipes 

• Endophytes – algae growing in other host algal species – for example: 

- Chlorochytrium/Sykidion spp. in a variety of host species 

- Myrionema strangulans in Palmaria and Enteromorpha 

sp. 

- Variety of Chlorophyta, Phaeophyta and Rhodophyta sp. 

in Cladophora, Polysiphonia and Ceramium 

- Many small filamentous epiphytes in gelatinous red and 

brown algae and particularly in decaying distal portions of 

Dumontia and Chorda 

• Epizoans – algae growing on faunal species – for example: 

- Audouinella sp. on hydroids 

- Ralfsia on Limpet shells 


• Endozoans – algae growing in faunal species – for example: 

- Audouinella sp., Melobesia and Epicladia in 

hydroids 

- Tellamia sp in Littorina littoralis. 

- Blue-green species, reproductive phases and 

Chlorophyta sp. boring in various periwinkle, 

limpet and mussel shells 

• Epilithic – algae growing over the rock surface – for example: 

- Encrusting corallines such as Lithothamnion, 

- 

Phymatolithon. 

Other encrusters such as Hildenbrandia and Ralfsia 

There is no systematic approach to intertidal rocky shore sampling, but all subhabitat 

types present should be identified and sampled. Due to the nature of algal sampling 

there is no guarantee of collecting or identifying all species present on a stretch of 

shore. To ensure maximum species richness is recorded, it is advised that sampling 

commence at the lower littoral zone of the shore working up the shore from low tide 

and covering the full tidal range of the shore. It is essential that the kelp zone is 

uncovered to expose those species attached to the stipes, and the lower shore 

rockpools which may be densely filled with a number of foliose and filamentous red 

species. Many low shore species may be found in rockpools. Searching should cover a 

wide extent of the shore and not be restricted to a single transect line to ensure all 

potential habitats are explored. Large rockpools can provide a wealth of algal 

diversity including many morphological forms such as encrusting and erect coralline 

forms, filamentous, gelatinous and cartilaginous forms. Turfs consisting of numerous 

red, brown and green species may be located in moist crevices, on the sides of 

boulders and steep rock outcrops and on overhangs. Often these turfs are covered over 

by a canopy layer of Fucus or other large conspicuous, cartilaginous forms. Due to the 

fine, filamentous and often microscopic nature of some tuft forming species it is 

advisable to take a scraping of the area and collect in a specimen tube, this is also 

applicable to the upper shore green mats. 


Some species have distinct vertical zonation patterns on the shore which may help 

with shore searching. Many red species are found on the lower littoral and sublittoral 

areas of the shore, therefore it is essential that sampling should take place on a spring 

low tide to ensure the lower littoral gets fully uncovered. Many of these species are 

found attached to the stipes of kelp or large, cartilaginous species or may be found 

within crevices to avoid the force of the waves. Brown algal species can generally be 

found throughout the intertidal, although they have quite limited diversity on the 

upper shore. Many of the brown species are quite conspicuous and easier to locate 

such as the kelp and fucoid species which often cover large areas or the intertidal and 

subtidal. Other filamentous species can be more difficult to find but may be found in 

amongst turfs or on various species including red and green algae. The green algae are 

more commonly found on the upper shore often forming mats on the rock surface but 

are also found attached to larger algae. Green patches of algae are also found scattered 

throughout the mid-littoral both on the open rock surface and within rock pools but 

Ulva sp. may form patches on the lower shore and within rockpools. 

More descriptive location details are given for each of the species from the reduced 

species list within the individual species descriptions. 

Although collection of specimens should be kept to a minimum it is important to 

collect whole plants along with stipe and holdfast, as these may be important for 

identification. Reproductive structures may also be important for classification and 

identification as they may help distinguish between two very similar species. Some 

species also have alternative phases in their life history which may be 

morphologically very different, so may key out as separate entities. There may also be 

seasonal difference in appearance due to new growth or reproductive bodies. Plants 

with thin membranous parts may lose these in autumn and winter storms, leaving only 

the tougher midrib or stipe. Taking some of these factors into account, it is 

recommended that sampling take place consistently at the same time of year 

preferably between May and early October due to increased levels of species richness 

during this time. Sample collections take on average 90 to 120 minutes by two or 

more persons, but this may vary according to the extent and width of the shore. 


Specimens should be collected and retained in either small plastic containers or plastic 

bags but not kept in water as this may aid decomposition, they must be kept cold and 

damp. It is useful to take a knife and forceps for collecting certain types of plants. 

Also take a field sheet and species check-list (Tables 1 and 2). Within the field 

sampling sheet basic information is required on shore name, time, date and tidal 

height as well as the general nature of the shore. The shore descriptions box enables a 

rough description of the shore to be noted, e.g. shore wide with large intertidal with a 

sandy bay to the west consisting mainly of one large rock outcrop within which are 

variously sized rockpools and a small cave on the upper shore to the east. Dominant 

shore type mainly refers to the type of hard substrate such as the presence of large 

rock outcrops, shingle, boulders etc. 

Basic descriptions of dominant shore types 

Rock ridges/platforms/outcrops – these refer to large areas of stable hard substrata 

forming either ridges across the shore, large flat rocky areas (platforms) or stand alone 

areas of rock jutting seaward which may also be cut off at high tide (outcrops). 

Irregular rock – large rocky areas that cannot be described as any of the above. 

Boulders – these generally refer to large rocks with small boulders measuring >20cm 

in diameter, medium boulders >50cm and large boulders >100cm. 

Steep vertical rock – this is relatively self explanatory but may also include rocky 

cliff faces that are found at low water. 

Non specific hard substrate – this refers to small rocky areas and can include 

artificial hard substrate, slip ways and harbour walls. 

Pebbles/stones/small rocks – general rocks smaller than 20cm in diameter. 

Gravel/shingle – rocks smaller than 1cm in diameter. 

Subhabitat type refers to the smaller habitats within the full range of the shore and 

includes rockpools of various sizes, crevices, overhangs etc. The general comments 

section should be used to note if there is any large abundance of opportunists, 

freshwater seepage or any information of interest that may be important for future 

referrals. 


Table 1: Field sampling sheet to record basic shore descriptions. 

General Information 

Shore Name Date 

Water Body Tidal Height 

Grid Ref. Time of Low Tide 

Shore Descriptions 

Examples of general shore descriptions are given on page 9 

Presence of Turbidity Yes =0 Sand Scour Yes =0 No =2 

(known to be nonanthropogenic) 

No =2 Chalk Shore Yes =0 No =2 

Dominant Shore Type Subhabitats 

Rock Ridges/Outcrops/Platforms =4 Wide Shallow Rock Pools 

=4 

Irregular Rock =3 (>3m wide and 6m long) =4 

Steep/Vertical Rock =2 Deep Rockpools (50% >100cm deep) =4 

Non-specific hard substrate =2 Basic Rockpools (none of the above) =3 

Pebbles/Stones/Small Rocks =1 Large Crevices =3 

Shingle/Gravel = 0 Large Overhangs and Vertical Rock =2 

Dominant Biota 

Ascophyllum 

Fucoid 

Others habitats (please specify) =2 

Rhodophyta mosaics Caves =1 

Chlorophyta None =0 

Mussels Total Number of Subhabitats 

Barnacles 

Limpets 

Periwinkles 

General Comments 

>4 3 2 1 0 

To include comments on any anthropogenic influence, presence of artificial structures or 

sea defences. General uses and impacts 


Milford Haven 

West Angle 

This was a moderately exposed and west facing sandy bay situated just outside of 

Milford Haven. The main sampling area was to the south of the bay consisting of 

large rock platforms. Mid and upper shore areas of the site appeared to be relatively 

devoid of algal species with large areas of bare rock ridges and platforms. These flat 

areas of rock were dominated by barnacles which covered the majority of the shore. 

Upper shore fucoids were present but in low abundance and only on the side of rock 

outcrops facing away from the sea. Despite the main rock surfaces appearing to lack 

any abundant algal growth the lower shore provided substantial subhabitats numbers 

and types to produce a high diversity of lower shore species resulting in this site being 

one of the most species rich in the area. The lower shore was covered with a variety 

of rockpools and gave way to more steeply sloping rocks towards the low water mark. 

These steep rock faces provided areas of dense cover of algae including Himanthalia, 

indicating exposure to wave action. 

Port Hubberston 

This shore was located into Milford Haven opposite to Angle Bay and surrounded by 

numerous oil facilities. The main sampling area consisted of steep rock outcrops 

which limited the extent of the shore. Despite this a typical shore zonation of a 

sheltered was exhibited with dense cover of fucoids along the full extent of the 

intertidal particularly at the west end of the shore. Initial appearance suggested this 

shore to be lower in algal diversity than Angle Bay and this was highlighted by the 

general lack of subhabitat diversity. The lower shore gave way to shingle and 

boulders at the low water mark, therefore the sublittoral was underdeveloped 

contributing further to the lack of algal diversity. Where dense fucoid cover was 

devoid the shore became barnacle dominated. There were very few rockpools present 

on the mid and upper shore only and these tended to be quite small and shallow with 

limited species present. 

Sawdern Point 

This moderately exposed to sheltered shore consisted of a rock outcrop at the east end 

of Angle Bay. The rock surface was very rough in texture producing numerous 

crevices in which algal species could more easily attach. On the north side of the 

shore, nearest to Milford Haven, the shore type changed to large boulders and a less 

even shore giving rise to many subhabitat types. On the south side, which faces onto a 

more sedimentary area of Angle Bay, the shore is becomes classically sheltered 

densely covered with long stranded Ascophyllum. In general the shore didn’t appear 

to be very species rich. 


Table 2: Species lists for each of the areas 

Eng 

Scot 

Eng Wales Scot 

Species List 

Wales RoI NI Eng 

RoI NI Eng 

Greens Reds 

Blidingia sp. 1 1 1 Aglaothamnion/Callithamnion 1 1 1 

Bryopsis plumosa 1 Ahnfeltia plicata 1 1 1 

Chaetomorpha linum 1 1 1 Audouinella purpurea 1 

Chaetomorpha mediterranea 1 1 Audouinella sp 1 

Chaetomorpha melagonium 1 1 Calcareous encrusters 1 1 1 

Cladophora albida 1 Callophyllis laciniata 1 

Cladophora rupestris 1 1 1 Catenella caespitosa 1 1 

Cladophora sericea 1 1 1 Ceramium nodulosum 1 1 1 

Enteromorpha sp. 1 1 1 Ceramium shuttleworthanium 1 1 1 

Monostroma grevillei 1 Ceramium sp. 1 

Rhizoclonium tortuosum 1 Chondrus crispus 1 1 1 

Spongomorpha arcta 1 Corallina officinalis 1 1 1 

Sykidion moorei 1 Cryptopleura ramosa 1 1 1 

Ulothrix sp 1 Cystoclonium purpureum 1 1 1 

Ulva lactuca 1 1 1 Delesseria sanguinea 1 

9 12 8 Dilsea carnosa 1 1 1 

Browns Dumontia contorta 1 1 1 

Alaria esculenta 1 1 Erythrotrichia carnea 1 1 

Ascophyllum nodosum 1 1 1 Furcellaria lumbricalis 1 1 1 

Asperococcus fistulosus 1 1 Gastroclonium ovatum 1 

Chorda filum 1 1 Gelidium sp. 1 1 

Chordaria flagelliformis 1 Gracilaria gracilis 1 

Cladostephus spongious 1 1 1 Halurus equisetifolius 1 

Desmarestia aculeata 1 Halurus flosculosus 1 

Dictyosiphon foeniculaceus 1 Heterosiphonia plumosa 1 

Dictyota dichotoma 1 1 1 Hildenbrandia rubra 1 1 

Ectocarpus sp. 1 1 1 Hypoglossum hypoglossoides 1 

Elachista fucicola 1 1 1 Lomentaria articulata 1 1 1 

Fucus serratus 1 1 1 Lomentaria clavellosa 1 

Fucus spiralis 1 1 1 Mastocarpus stellatus 1 1 1 

Fucus vesiculosus 1 1 1 Melobesia membranacea 1 

Halidrys siliquosa 1 1 1 Membranoptera alata 1 1 1 

Himanthalia elongata 1 1 1 Nemalion helminthoides 1 

Laminaria digitata 1 1 1 Odonthalia dentata 1 1 

Laminaria hyperborea 1 1 Osmundea hybrida 1 1 1 

Laminaria saccharina 1 1 1 Osmundea pinnatifida 1 1 1 

Leathesia difformis 1 1 1 Palmaria palmata 1 1 1 

Litosiphon laminariae 1 Phycodrys rubens 1 

Pelvetia canaliculata 1 1 1 Phyllophora sp. 1 1 1 

Petalonia fascia 1 Plocamium cartilagineum 1 1 1 

Pilayella littoralis 1 1 1 Plumaria plumosa 1 1 1 

Ralfsia sp. 1 1 1 Polyides rotundus 1 1 

Saccorhiza polyschides 1 Polysiphonia fucoides 1 1 1 

Scytosiphon lomentaria 1 1 1 Polysiphonia lanosa 1 1 1 

Sphacelaria sp 1 Polysiphonia sp. 1 1 1 

Spongonema tomentosum 1 1 Porphyra leucosticta 1 

20 22 26 Porphyra umbilicalis 1 1 1 

Ptilota gunneri 1 

Rhodomela confervoides 1 1 1 

Rhodothamniella floridula 1 1 1 

40 34 36 

Total 69 68 70 


2. IDENTIFICATION OF SPECIMENS 

All specimens should be laid out in large sorting trays where fronds and fine 

filamentous structures can be separated out and become more visible, this may be 

assisted by placing small amounts in a petri dish and examining under low 

magnification (dissecting microscope). Mats of algae need to be carefully separated 

and pulled apart so that all species can be identified. For more detailed examination 

using a compound microscope, particularly of small filamentous and microscopic 

species, a small amount of the specimen may be removed and placed on a glass slide 

with a little water and glass cover slip laid over the top. Microscopic examination is 

usually necessary to identify many of the larger filamentous species and to find and 

identify the smaller ones that may live inside or attached to larger ones. 

Although identification of all species from the reduced species list can be achieved 

using this key, it may be necessary to confirm with descriptions and pictures from 

alternative keys. It is generally advisable to confirm all species identification with the 

appropriate guides and keys even those species that have been identified in the field. 

There is an amazing range of seaweed forms some of which can only be found by 

detailed field searching or under the microscope. But it is these morphological 

characteristics that are essential for identification. Some species may have their colour 

masked by an excess of other pigments – the red Porphyra usually looks brown, 

brown fucoids may sometimes appear green, old tips of Dumontia turn green, 

Ahnfeltia appears black as do some species of Polysiphonia. Therefore, it is essential 

to be aware of some of these pigment discrepancies before identification starts as this 

may lead to the use of the wrong key. 


The varieties of algae forms are briefly described with microscopic and field photos to 

illustrate such forms: 

• Filaments – a linear group of cells joined at their walls or a chain of cells 

o branched or unbranched 

o uniseriate (one cell thick) and multiseriate or monosiphonous filaments 

which may be covered with many smaller cells (> 1 cell thick/wide) 

Cells 

Uniseriate Multiseriate 

o macroscopic (large filaments visible with the naked eye) or 

microscopic (requires magnification) 

o free-living on rock or endophytic, endozoic, epiphytic (as described in 

above section) 

• Pseudoparenchymatous forms (growing by aggregation of filaments) or 

parenchymatous (composed of a mass of cells growing by cell division in 2 

or more planes), multiseriate: 

o Tubular – may appear flat as often sides are often compressed together 

giving the appearance of a ribbon shaped foliose plant. 

Mass of cells 

Ribbons 


o Foliose – plant is generally wide, flat and quite thin sometime only 1 

cell thick often leaf like in appearance 

• Encrusting forms – algae that grow over the rock surface with no erect 

system 

• Coenocytic forms – made up of acellular filaments, (not divided into cells) 

and cell contents move freely within the filament, multinucleate 

No cell divisions 

• Large cartilaginous forms – firm and tough but slightly flexible with leather 

like texture 


Special features that need to be considered in making identifications 

• Chloroplast morphology in cells (compound microscopic examination). 

Parietal 

Band/ ribbon shaped 

Reticulate 

o Parietal – forming a cylinder around the cell inside the cell 

wall 

o Axile – passing through the middle of the cell cavity 

o Simple – a non-perforated plate or cylinder 

o Band/ribbon shaped – a girdle almost completely encircling 

the cell 

o Discoid – often many discs per cell 

o Reticulate – a network – sometimes made up of lots of 

filaments of chloroplast material or sometimes formed by 

lots of perforations and lobes on a parietal cylinder 

• Pyrenoids –centre of formation of storage product in the chloroplast –stains 

blue-black with iodine in potassium iodide in green algae only because starch 

is the storage product. There may be a single or many pyrenoids per cell found 

in or extending from the chloroplast. 

Pyrenoids 


• Branching patterns: 

o Irregular – branching in no consistent pattern and cells of 

varying shapes and sizes 

Irregular 

o Alternate - arranged in two rows with branching 

alternating between sides 

o Opposite – branches appearing on both sides of the main 

axis directly opposite form each other 

Opposite 

o Secund – arranged on one side of the main axis 

resembling a comb 

Secund 

o Dichotomous – branches forking regularly into two equal 

branches, division always in pairs resembling the letter ‘Y’ 

Dichotomous 

o Subdichotomous – similar to dichotomous branching 

but with one branch of limited growth and the other 

continuing to grow 

Whorled 

Alternate 

Subdichotomous 

o Whorled – several branches radiating from the main axis at 

the same level, surrounding axis in a ring, often quite bushy 


• Reproductive structures – these can vary considerably between species 

therefore may aid with identification for example: 

o Fucus spiralis – the fruiting bodies/receptacles are 

inflated, round and often have a rim of sterile material 

o Fucus serratus – receptacles flattened with extended growth 

o Fucus vesiculosus – receptacles inflated, elongated and 

pointed 

o Pilayella littoralis – intercalary sporangia where the cells 

within which spores are contained are located between the 

base and apex of the plant 

o Ectocarpus sp. and Giffordia sp. – plurilocular 

sporangia (reproductive structures with many 

compartments) are located on stalks, may be 

elongated, spindle, ovoid or conical shaped 


Spermatangia 

Cystocarps 

o Sphacelaria sp. – reproductive body a propagule, which is a 

structure consisting of a multicellular branch that detaches from 

thallus 

o Mastocarpus stellatus – cystocarps (female) 

existing as knobbles and spermatangia (male) 

present as dark stains on the thallus 

o Halurus flosculosus – cystocarps and spermatangia 

present as cups of fruiting bodies on stalks 

Other characteristics of interest 

• Apical cell – a prominent cell at the apex or tip of plant for 

example in Dictyota dichotoma 

• Cortication – an outer covering of small cells 

• Frond – the erect part of a seaweed often used in the 

description of foliose algae 


Spermatangia 


Axial cell 

• Distal– Towards the base or point of attachment 

• Holdfast – the structure for attachment to substrate, may be root-like, single 

cell or group of cell, disc or claw-like. Apparent encrusting forms may 

sometimes be basal portions of erect plants e.g. some encrusting calcareous 

forms may just be expanded basal portions of Corallina, some non-calcareous 

red ones may be bases of Mastocarpus 

• Lamina – the blade of flat, leafy or foliose algae 

• Membranous – forming a thin layer, may be semi-transparent, 

often sheet-like 

• Pinnate – branching arranged like feather plumes 

often in a single plane 

• Polysiphonous – a ring of cells (siphons or pericentral cells) 

located around a central or axial cell 

Pericentral cells 

Claw-like holdfast Discoid holdfast 


• Stipe – basal stalk-like portion arising from the holdfast and 

bearing lamina 

• Terete – cylindrical in cross section 


A FIELD KEY TO THE BRITISH SEAWEEDS 

This identification guide is driven solely by the Water Framework Directive and only 

includes those species listed as those most frequently found on shores within the 

British Isles and Republic of Ireland. This list is referred to as the reduced species list 

(RSL). Separate lists have has been compiled for Northern Ireland, Southern 

England/RoI/Wales and Northern England/Scotland. 

This key is specific to the RSL and may exclude a number of characteristics and 

morphological forms that may usually be found in algal identification keys. 

Chlorophyta The green algae are generally grass green in colour and tend to be 

delicate in morphological form with many existing as small filamentous, foliose or 

microscopic forms. They often turn brown during the decomposition process and may 

appear brown in the field due to the external presence of epiphytic diatoms. Most 

Chlorophyta species are located at the top of the shore although Ulva, Enteromorpha 

and Cladophora are also common on the mid and lower shore. Page 23 


Phaeophyta The brown algae constitute many of the large cartilaginous forms, 

which can cover large areas of the shore, as well as finer forms, therefore have a large 

morphological range. They may be olive-green, or various shades of brown, from 

golden to dark brown. Bleaching and decomposition can cause a change in colour to a 

browny yellow or green. Colour may also change considerably under the microscope 

due to the light so this needs to be taken account of when examining the small 

filamentous species. Page 26 


Rhodophyta The red algae exhibit a range of colours from dark red to black through 

to shades of pink, purple and brown and take on a variety of morphological forms. 

The decomposition of Rhodophyta species results in a change in colour whereby many 

cells turn green, they may also be bleached in bright sunlight changing to brown or 

yellow in colour. Therefore it is necessary to use fresh material in order to assist with 

the first line of taxonomic classification and to reduce confusion with some 

Phaeophyta species. Rhodophyta species are more commonly found on the mid to 

lower shore. Page 31 


Chlorophyta Species 

Group A Plants are flattened, often thin and delicate may be easy to tear, and 

also tubular, cylindrical or hollow, which is often evident on cross 

section of the specimen. Smaller forms may also take on a slightly 

filamentous but cylindrical appearance (filiform) but microscopic 

examination will clarify this as they will be multiseriate (several cells 

wide). 

Group B Plants filamentous in form, tend to be very fine, delicate and hair like. 

Generally consist of a single or numerous filaments of linearly 

arranged cells which may be more clearly seen under microscopic 

examination. These species are uniseriate (one cell wide). 

Group C Plants microscopic, growing on or in other species of algae or rocks 

and shells, may be uni- or multi-cellular but are often difficult to 

locate. 

Sykidion moorei 

(this species is a single round cell located within Blidingia sp. only) 

Group D Plants are siphonous, they do not have cross walls, and cellular 

material moves freely throughout the filaments. They resemble those 

species of Group B with a filamentous appearance. 

Bryopsis plumosa 

(this species tends to be very fine, delicate and feather like with a 

regular opposite branching pattern in a single plane only) 


Group A 

1. Plants completely flattened……………………………………………………2 

1. Plants tubular or appearing slightly filiform…………………………………..3 

2. Plants one cell thick only, forming a very delicate and thin membrane, may 

tear very easily and with a sheet-like appearance almost translucent 

2. 

Monostroma sp. 

Plants two cells thick, forming a tougher thicker sheet, often bright green in 

colour Ulva lactuca 

3. Cells usually 4-12um wide with a basal disc and no rhizoidal cells, small 

filiform plants often found as a thin spongy mat or layer on Fucus or upper 

shore rock surface Blidingia sp. 

3. Cells greater than 12um, tubular plants, may be branched or unbranched often 

found in dense patches covering vast areas of the upper and mid shore 

attached by rhizoidal cells Enteromorpha sp. 

Group B 

1. Plants unbranched or few branches……………………………………………2 

1. Plants highly branched………………………………………………………...6 

2. Rhizoidal growths or false branching of 1-3 cells long, cells generally longer 

than wide forming long filaments, forming a felty green mat at the top of the 

shore Rhizoclonium tortuosum 

2. Rhizoidal growths absent……………………………………………………...3 

3. Plants with a reticulate (net-like) chloroplast…………………………............4 

3. Plants with a single band/cup shaped or parietal chloroplast where the 

chloroplast lines the inner cell wall Ulothrix sp. 


4. Plants forming a soft woolly mass of fine filaments often tangled around other 

algae on the upper shore and in rock pools Chaetomorpha mediterranea 

4. Plants do not form a soft woolly mass………………………………………..5 

5. Plants form a tough and wiry mass of thick filaments giving appearance of 

green garden/fishing wire or wire wool Chaetomorpha linum 

5. Plants solitary filaments, cells large often appearing bead-like, usually found 

growing in sandy pools Chaetomorpha melagonium 

6. Cells with a dense reticulate chloroplast appearing uniformly green…………7 

6. Reticulate chloroplast not dense, with net work of fibrils clearly visible, 

appearance of false discoid chloroplasts and club shaped apical/terminal cells, 

plants often quite tufted and often entwined to form rope like growths 

Spongomorpha arcta 

7. Branching usually multidichotomous often with up to 6 branches arising from 

a single axial cell, often dark green in colour and may be quite coarse in 

texture Cladophora rupestris 

7. Branching often comb-like but may also have dichotomous branches, lighter 

green in colour Cladophora sericea 

7. Light green in colour with rounded apical/terminal cells, cells often long and 

slender with narrow apical cells Cladophora albida 


Phaeophyta Species 

Group A Plants are generally large and cartilaginous in form, consisting of a 

thick, tough and leathery frond. This group may take on a variety of 

morphological forms composed of wide flat fronds, channelled fronds, 

simple single blades and highly branched forms. These plants are not 

hollow except for the presence of air bladders which may be found in 

some species. 

Group B Plants consist of a thick thread like form ranging from 1mm to 5mm 

wide. These are often cylindrical but may also be slightly flattened but 

are not hollow and do not contain air bladders. Some species may 

appear as a single rope like plant, other species may be highly 

branched and more delicate in form. 

Group C Plants filamentous in form, tending to be very fine, delicate and hair 

like. Generally consist of a main axis up to 1mm thick and numerous 

filamentous branches usually less than 0.25mm. Branches may either 

be uniformly arranged or irregular. Filaments may be long, short, stiff 

or floppy, separated or tangled together into woolly cords. Usually less 

than 15cm long, but may extend up to 30cm. Found growing 

epiphytically on a host species or independently. Many species require 

microscopic assistance for identification. 

Group D Plant flattened and quite thin may be easily torn but generally quite 

elastic. Consist of both branched and unbranched forms although not 

numerously branched. 

Group E Plants tubular and hollow from 2mm to 12mm wide. May be easily 

torn as they can be quite thin and membranous. 

Group F Plants forming distinct crusts or cushions on the rock and other hard 

surfaces. 


Group A 

1. Plants with distinct midrib……………………………………………….........2 

1. Plants without distinct midrib………………………………………...….........5 

2. Plants with a prominent claw-like holdfast (basal attachment) present, with 

long, wide fronds that may be easily torn. Characteristic of exposed shores. 

Alaria esculente 

2. Plants with indistinct disc-like basal attachment…………….…………..........3 

3. Plant with air bladders set in frond, usually in pairs either side of the midrib, 

(no. of bladders variable depending on degree of exposure) Fucus vesiculosus 

3. Air bladders absent from plant………………………………….……………..4 

4. Frond spirally twisted and present on the upper shore Fucus spiralis 

4. Frond edge serrated and generally present on the lower shore Fucus serratus 

5. Plant with in-rolled frond forming a distinct channel Pelvetia canaliculata 

5. Frond not channelled…………………………………………………………..6 

6. Air bladders present……………………………………………………...........7 

6. Air bladders absent……………………………………………………………8 

7. Plant with pod-shaped air bladders divided internally by cross-walls 

(resembling pea pods). Branching alternate giving a zig-zag appearance 

Halidrys siliquosa 

7. Air bladders ovoid at intervals along the main axis of the plant. 

Dichotomously branched but fairly infrequent, stalked receptacles often 

present along the main frond. Characteristic of sheltered shores. 

Ascophyllum nodosum 


8. Thallus consisting of a large wide flat frond…………………………….........9 

8. Thallus rope-like extending from a button or mushroom shaped holdfast, 

frond often very long, sometimes flat and divided Himanthalia elongata 

9. Flat expanded part of thallus not divided, with wavy edge and crinkly centre 

Laminaria saccharina 

9. Main thallus smooth and generally divided, giving large finger like 

appearance……………………………………………………………………10 

10. Holdfast a large and warty bulb with ribbon-like, wavy stipe 

Saccorhiza polyschides 

10. Holdfast simple and claw shaped……………………….……………………11 

11. Stipe smooth and flexible and slightly flattened at the top, can be almost 

entirely undivided in sheltered areas Laminaria digitata 

11. Stipe stiff, round and upright, generally rough and covered with red algal 

epiphytes Laminaria hyperborea 

Group B 

1. Plant completely unbranched, cylindrical bootlace extending to 8m in length. 

Chorda filum 

1. Plant variously branched……………………………………………………....2 

2. Branching mostly alternate, frond flattened with long main axis, older plants 

exhibit short spine-like branchlets giving a serrated appearance. 

Desmarestia aculeata 

2. Branching mostly irregular……………………………………………………3 

3. Branches numerous, often with a covering of fine hairs, slightly gelatinous 

and slippery. Chordaria flagelliformis 

3. Branches more coarse in texture. Dictyosiphon foeniculaceus 


Group C 

1. Plants consist of unbranched filaments growing as small tufts on larger 

seaweed…………………………………………………………...…………...2 

1. Plants branched and occasionally tangled into woolly cords…………...……..3 

2. Uniseriate filaments found growing epiphytically on Fucus sp. 

Elachista fucicola 

2. Multiseriate filaments found growing on a number of large brown seaweed 

particularly Alaria and Chorda. Litosiphon sp. 

3. Plants stiff, retaining rigidity whilst in water…………………………..……...4 

3. Plants flexible in water often limp and floppy…………………………...........5 

4. Plant usually less than 2-3cm, with irregular branching and often appearing as 

tufts on other seaweed. Sphacelaria sp. 

4. Branching very regular, whorled around main filament resembling a pipe 

cleaner and up to 25cm long. Cladostephus spongiosus 

5. Filaments tangled into woolly cords, up to 20cm long often found growing on 

Fucus sp. Spongonema tomentosum 

5. Filaments not tightly tangled into cords but may be slightly clumped………..6 

6. Chloroplasts appearing as long ribbon shapes, with sporangia present as 

elongated spindles on stalks. Ectocarpus sp. 

6. Chloroplasts present as small discs with sporangia appearing as swollen cells 

within the main filament (intercalary). Pilayella littoralis 


Group D 

1. Plant dichotomously branched, tips often appearing two pronged, quite thin 

and membranous. Dictyota dichotoma 

1. Plant consisting of simple undivided ribbons, thin and membranous. 

Group E 

Petalonia sp. 

1. Plant unbranched and hollow with regular constrictions giving the appearance 

of a string of sausages. Scytosiphon lomentaria 

1. Plant hollow with irregular width and length, often with rough texture due to 

presence of sporangia as small spots. Asperococcus fistulosus 

Group F 

1. Plant appearing as a brown/black crust generally growing on rocks surfaces 

and limpets. Ralfsia sp. 

1. Plant appearing as a spherical, gelatinous and bulbous hollow sack. 

Leathesia difformis 


Rhodophyta Species 

Group A Plants calcareous, hard and limy present as both a crust forming over 

the surface of rocks and algal fronds, including microscopic forms, and 

as an erect system. Generally pink or purple in colour, but turning 

white on bleaching. This group also includes those non-calcareous 

encrusting forms, present as a large stain on the rock surface. 

Group B Plants with main blade or frond flattened or compressed, often leaflike, 

may occasionally be in-rolled, often with a wide blade which may 

vary from tough and leathery to thin, membranous and slightly elastic. 

This group may take on a variety of morphological forms composed of 

wide, flat or channelled fronds, simple single blades, split blades and 

highly branched forms. 

Group C Plants not completely flattened, thin or leaf-like, generally thick, 

cartilaginous, wiry or gelatinous, appearing as a course or stiff 

cylindrical structure but may also be slightly compressed, bead-like or 

hollow ranging from 0.5mm to 5mm wide with no filamentous 

branching. Some species display minimal irregular branching, other 

species may be highly and regularly branched. 

Group D Plants consisting of thread-like, multiseriate forms (several cells in 

width), consisting of a main axis up to 1mm thick and numerous 

filamentous branches usually less than 0.25mm and of varying length. 

Branches may either be uniformly arranged or irregular and are often 

fine, delicate and hair like. Requires microscopic identification. 

Group E Plants very fine, filamentous and delicate, only one cell wide and may 

display limited branching or be highly and regularly branched. This 

group includes the small and epiphytic plants present as either prostrate 

or erect forms often appearing as a small spot or tuft on rock surfaces 

and other algae. Microscopic identification is necessary. 


Group A 

1. Plant calcareous……………………………………………………………...2 

1. Plant non-calcareous forming a deep red staining on the rock surface 

Hildenbrandia rubra 

2. Plant appearing filiform, consisting of a jointed calcareous upright system 

resembling small bones and generally located in rockpools 

Corallina officinalis 

2. Plant forming a small or large crust or layer over the surface of rocks and 

other algae……………………………...………..…………………………….3 

3. Plant microscopic appearing as a small disc of radiating cells present on a 

number of red algal species and hydroids Melobesia membrancea 

3. Plant forming large crust over the rock surface, consisting of various textures 

and shades or pink, purple and red, may also be found covering the outer 

frond of algal species such as Polyides Calcareous encrusters 

Group B 

1. Plant with midrib or veins present………………………………………...…..2 

1. Plant without midrib or veins………………………………………………….5 

2. Plant with distinct midrib…………………………………………………...…3 

2. Plant with indistinct, faint and interrupted midrib, blade quite wide and leafy 

but with course cylindrical stipe Phyllophora sp. 

2. Plant without a midrib but with macro/microscopic veins present, blade edges 

often frilly and tatty looking with disc holdfast Cryptopleura ramosa 


3. Branches and bladelets arising from the midrib only consisting of fine, 

narrow, delicate pointed fronds Hypoglossum hypoglossoides 

3. Plant with branching from the outer frond margin and usually much branched 

also with fine delicate and relatively narrow fronds Membranoptera alata 

3. Plant with branching from the main stipe only…..….……………..………….4 

4. Plant with blade edge slightly ruffled resembling beech leaves, quite thin and 

delicate with wide blade Delesseria sanguinea 

4. Plant with slightly serrated blade edge resembling oak leaves quite thin and 

delicate with wide blade Phycodrys rubens 

5. Plant simple, split or lobed but not highly branched…………………..……...6 

5. Plant variously and highly branched………………………………………..…9 

6. Plant membranous, thin and slightly elastic with no divided sections although 

main frond may occasionally be split…………………………………………7 

6. Plant tough with wedge shaped divisions in main frond………………...……8 

7. Plant with holdfast or attachment disc based in the centre of the frond 

7. 

Porphyra umbilicalis 

Plant with holdfast at the base of the frond, very delicate and found growing 

on other algae particularly Fucus sp. Porphyra leucosticta 

8. Plant very tough and leathery, slightly cartilaginous, branching from base only 

with splits or wedge shaped divisions Dilsea carnosa 

8. Plant tough but floppy and fleshy, irregular divisions with branchlets often 

occurring from main blade Palmaria palmata 

9. Plant with dichotomous branching…………………………………………...10 

9. Plant without dichotomous branching………………………...……………..11 


10. Plant completely flattened often with broad wide wedge shaped frond often 

quite tough often with smooth fronds Chondrus crispus 

10. Plant with in-rolled gutter like frond forming a channel quite dark in colour 

and tough often with rough frond and edges due to presence of reproductive 

bodies Mastocarpus stellatus 

11. Plant with regular branching pattern…………………………………………12 

11. Plant with irregular branching……………………………………………….13 

12. Plant quite fine and delicate with regular comb-like branching, very highly 

branched very pink in colour Plocamium cartilagineum 

12. Plant with small but regularly alternate branching, with a tooth-like outline, 

usually deep pink/red in colour Odonthalia dentata 

13. Plant highly divided into irregular but broad fan shaped sections with wide 

fronds quite floppy and fleshy Callophyllis laciniata 

13. Plant highly branched often opposite but not obviously, plant terete in lower 

section but often broader and flattened towards the tips Gelidium sp. 

Group C 

1. Plant visibly constricted at intervals…………………………………………..2 

1. Plant not constricted at intervals……………………………………………....4 

2. Constrictions at irregular intervals, plant irregularly branched with segments 

variable, some flat some cylindrical, small and creeping 

Catenella caespitosa 

2. Constrictions at regular intervals…………………………...…………………3 


3. Plant bead like and deep pink in colour often with a number of branches 

extending from each articulation Lomentaria articulata 

3. Plant with branching generally in one plane sometimes appearing flat 

Lomentaria clavellosa 

4. Branching dichotomous……………………………………………………….5 

4. Branching irregular, regular, opposite or alternate but not dichotomous……..7 

5. Plant consisting of small bundles present at the plant tips, base of branchlets 

constricted Gastroclonium ovatum 

5. Branches not constricted at base with no bundles present at plant tip………...6 

6. Plant cylindrical in cross section regularly dichotomously branched with clawlike 

holdfast Furcellaria lumbricalis 

6. Plant cylindrical in cross section regularly dichotomously branched with disclike 

holdfast Polyides rotundus 

7. Branching regular……………………………………………………….…….8 

7. Branching irregular……………………………………………….…………...9 

8. Plant thick and fleshy with alternate branching occurring in a single plane 

appearing flattened Osmundea pinnatifida 

8. Plant thick and fleshy with branching alternate or opposite, cylindrical with 

branching in all planes not flattened Osmundea hybrida 

9. Plant gelatinous………………………………………………………………10 

9. Plant not gelatinous…………………………………………………………..11 

10. Plant hollow often green at the tips of old plants where rotting has taken place, 

with limited branching Dumontia contorta 

10. Plant very squashy, slippery and elastic very few branches present 

Nemalion helminthoides 


11. Plant black and wiry with disc-like holdfast, narrow branching very irregular 

and often found in sandy environments Ahnfeltia plicata 

11. Plant elastic, long and straggly, branching very irregular sometimes becoming 

bushy, cartilaginous and firm Gracilaria gracilis 

Group D 

1. Plant polysiphonous………………………………………………………..…2 

1. Plant not polysiphonous………………………………………………..……..4 

2. Main branches polysiphonous, smaller branches monosiphonous and 

numerous, appearing tufted Heterosiphonia plumosa 

2. Plant polysiphonous throughout………………………………...…………….3 

3. Plant found growing epiphytically on Ascophyllum species often quite course 

and tufted in texture Polysiphonia lanosa 

3. Plant with 12-20 siphons, lower, older filaments of plant covered with small 

cells (corticate), branching irregular with upper parts of plants more densely 

covered, generally dark brown or black in colour Polysiphonia fucoides 

3. Not as above Polysiphonia sp. 

4. Plant appearing banded, dichotomously branched with terminal branches 

generally in-rolled…………………………………………………………..…5 

4. Plant not appearing as above………………………………………………..…6 

5. Plant almost or completely covered in small cells (corticate), plants quite 

variable, irregularly dichotomous, terminal branches tightly in-rolled or 

straight, very common Ceramium nodulosum 

5. Plant with multicellular spines present on the outside of filaments, not 

completely corticate, dichotomously branched and terminal branches strongly 

in-rolled Ceramium shuttleworthianum 

5. Plants not as above Ceramium sp. 


6. Branching whorled around main axis and highly branched resembling a bottle 

brush Halurus equisetifolius 

6. Branching not whorled……………………………………………………..…7 

7. Branching opposite…………………………………………………………....8 

7. Branching not opposite………………………………………………………..9 

8. Plant with branching opposite and long and short branches regularly alternate, 

plants dark red and delicate but slightly rigid 

Ptilota gunneri 

8. Plant with opposite branching but long and short branches not regularly 

alternate, plants dark purple or brown and very delicate and fine 

Plumaria plumosa 

9. Plant with claw-like holdfast, quite long and highly branched, firm and 

cartilaginous often appearing straggly Cystoclonium purpureum 

9. Plant with discoid holdfast, often densely branched, terminal branches often 

short and tufted Rhodomela confervoides 

Group E 

1. Plant highly branched……………………………………………………..…..2 

1. Plant with limited branching…………………………………………………..3 

2. Plant with bone shaped cells giving jointed appearance, with pointed terminal 

cells, bright pink in colour, with long branches, quite delicate and hair-like 

2. 

Halurus flosculosus 

Plant densely and usually alternately branched often appearing tufted, found 

growing on rocks and other algae, present in a variety of forms, often quite 

small and spongy Callithamnion/Aglaothamnion sp. 


3. Plant generally found attached to rock surface and macroscopic……………..4 

3. Plant found growing on other algae and typically microscopic…………....….5 

4. Plant found growing on sand covered hard surfaces, pyrenoids highly visible 

under the microscope with flower shaped chloroplasts, branching limited 

Rhodothamniella floridula 

4. Plant found in turfs generally in moist overhangs, branching limited with 

reticulate (network system) chloroplast covering whole of cell 

Audouinella purpurea 

5. Plant with star shaped chloroplast several cells long commonly found on 

Polysiphonia and Ceramium species Erythrotrichia carnea 

5. Plant taking a variety of small microscopic forms, either as small erect forms a 

few cells long or appearing as red spots or stains on other algae with erect 

systems creeping throughout or over other algae 

Audouinella sp. and Erythrocladia irregularis 


SUMMARY OF SPECIES 

Species List General Morphology General Location on the shore 

Greens 

Blidingia sp. 


Chaetomorpha linum 

Chaetomorpha 

mediterranea 

Chaetomorpha 

melagonium 

Cladophora albida 

Cladophora rupestris 

Cladophora sericea 

Enteromorpha sp. 

Monostroma grevillei 

Rhizoclonium tortuosum 


Green mat, spongy, foliose but may appear 

filamentous 

Fine feather like, very delicate, often quite 

small 

Bright green, resembling thin curly garden 

wire or wire wool 

Very curly, looks like thin wool, often 

present in dense patches 

Consist of a solitary robust strand, with 

obvious cells appearing beaded 

Filamentous, highly branched, light green in 

colour 

Filamentous, highly branched can be tufted, 

dark green and slightly coarse 

Filamentous, highly branched can be tufted, 

light green 

Foliose and tubular, often ribbon shaped, 

may be crinkly, very green 

Very thin, wide, foliose and membranous, 

pale green, easily torn 

Thin, filamentous and branched, forming 

dense green mats 

Filamentous, highly branched, light green in 

colour quite tufted 

Generally found on the upper shore on 

rock surface or lower on Fucus fronds 

Found on the mid shore in rock pools, may 

be hard to find 

Found on mid to upper shore on rock 

surface or in very shallow pools also on 

mud in estuaries 

Found on mid to upper shore, often tangled 

around other species 

Found in sandy bottomed rock pools on the 

mid shore 

Found throughout the intertidal in 

numerous habitats, often epiphytic 


numerous habitats 


numerous habitats 

Found throughout the intertidal but very 

common on upper shore and around 

freshwater 

Found most frequently on upper shore 

(commonest in spring) on rock surface or 

rock pools 

Found on upper shore particularly on open 

rock surfaces and harbour walls 

Found mid littoral often as part of mat as 

turf forming species 

Sykidion moorei Unicellular, single large round cell Found in Blidingia sp. 

Ulothrix sp Fine, filamentous, green and unbranched 

Ulva lactuca 

Foliose, with wide blade looks like lettuce 

leaf and very green 

Found mainly on mid and upper shore 

rocky surfaces, often growing on Fucus sp. 

Found throughout the littoral down to 

lower littoral fringe 


40

Browns 

Alaria esculenta 


Asperococcus fistulosus 

Chorda filum 

Chordaria flagelliformis 

Cladostephus spongious 


Dictyosiphon 

foeniculaceus 

Dictyota dichotoma 

Ectocarpus sp. 


Fucus serratus 

Fucus spiralis 

Fucus vesiculosus 


Himanthalia elongata 

Laminaria digitata 

Laminaria hyperborea 

Up to 2 m long, with distinct midrib and 

wide, frilly, easily torn blade 

Large and cartilaginous with regular air 

bladders along frond 

Ribbon-like, foliose, hollow and tubular 

with rough frond surface 

Long and rope-like, completely unbranched, 

cartilaginous 

Filiform and branched covered with tiny 

hairs, may be gelatinous 

Coarse, highly branched and tufted, looks 

like pipe cleaner 

Filiform, branched often short and spine 

like with serrated appearance 

Found on lower littoral in subtidal fringe 

on wave exposed areas 

Found in mid to upper littoral areas but is 

generally typical of sheltered shores 

Found in the mid littoral in wide shallow 

rock pools with sandy bottom; also in 

sheltered shallow sublittoral 

Found mainly in mid littoral in wide 

shallow rock pools with sandy bottom 



Found throughout intertidal mainly in 

overhangs, damp places and turfs/mats; 

common in sandy areas 



Filiform and branched covered with tiny Found mainly in mid littoral in wide 

hairs not gelatinous 


Thin membranous and foliose, with distinct Frond on mid to lower littoral, mainly in 

dichotomous branching 

rockpools of various sizes 

Fine, filamentous, highly branched and Found growing throughout littoral, often 

often tangled into loose cords 

on sandy areas and attached to other algae 

Small, filamentous, unbranched and tufted, Found throughout the littoral growing 

brush-like 

Cartilaginous, with midrib and frond edge 

epiphytically on Fucus sp. 

serrated Grows mainly on lower littoral 

Cartilaginous, with midrib and frond 

spirally twisted 

Cartilaginous, with bladders in pairs either 

side of midrib, no. of bladders varies with 

Grows mainly in upper littoral 

degree of exposure Grows mainly in mid littoral 

Cartilaginous, with pod-shaped air bladders Found in deep rockpools on mid to lower 

and zig-zag branching 

littoral 

Cartilaginous, rope-like but flat, branched Found on open rock platforms mainly on 

with distinct button holdfast 

Large, cartilaginous, claw holdfast, wide 

lower littoral 

divided frond with smooth flexible stipe Found in littoral/subtidal fringe 

Large, cartilaginous, claw holdfast, stiff 

stipe covered in epiphytes with wide 

divided frond Found in littoral/subtidal fringe 


41

Laminaria saccharina 

Cartilaginous, large frond, unbranched with 

wavy edge, and crinkly centre Found in littoral/subtidal fringe 

Grows in a variety of habitats but mainly in 

the mid to lower littoral on rock 

Fine, filamentous, unbranched and growing Grows mainly on Alaria and Chorda, so 

in small tufts 

Cartilaginous, with frond in-rolled forming 

located in mid to lower littoral 

distinct channel Grows only in upper shore regions 

Thin, membranous, foliose, undivided Found throughout the littoral on various 

frond and ribbon-like 

substrates 

Fine and filamentous, branched, may form Found throughout the littoral particularly 

mass of filaments 

Crust, black growing on rock surface or 

on sandy substrate 

limpets 

Large and cartilaginous, with warty bulb 

Found throughout the littoral 

holdfast and wavy ribbon stipe Grows in the littoral/sublittoral fringe 

Tubular, hollow, unbranched with regular Found throughout the littoral but common 

constrictions 

in wide shallow and sandy rockpools 

Found growing in turfs in overhangs 

Filamentous, branched and coarse growing throughout the littoral or attached to 

as stunted tufts 

Corallina in pools 

Filamentous, branched and tangled into Often grows on Fucus so found throughout 

woolly cords 

the littoral 

Leathesia difformis Spherical, gelatinous, bulbous hollow sack 

Litosiphon laminariae 

Pelvetia canaliculata 

Petalonia fascia 

Pilayella littoralis 

Ralfsia sp. 

Saccorhiza polyschides 

Scytosiphon lomentaria 

Sphacelaria sp 

Spongonema tomentosum 

Reds 

Aglaothamnion/ 

Callithamnion 

Ahnfeltia plicata 


Audouinella sp 

Calcareous encrusters 

Callophyllis laciniata 


Fine, delicate, densely branched small and Growing in turfs or mats in overhangs and 

spongy appearing tufted 

crevices in the mid to lower shore 

Black, coarse and wiry, branching irregular Growing in sandy bottom rockpools in mid 

with disc holdfast 

to lower littoral 

Fine, filamentous, few branches and turf Growing in turfs or mats in overhangs and 

forming, mossy 

crevices throughout the littoral 

Small filaments, microscopic, few cells Grow epiphytically on a number of species 

long, epiphytic 

so found throughout the littoral 

Calcareous, in various shades of pink and Found growing on hard substrate 

purple covering rock surfaces; white when throughout the littoral zone and commonly 

bleached 

in rockpools 

Floppy and fleshy, divided broad fan Grows in the lower littoral/sublittoral 

shaped sections 

Small, creeping, variable with irregular 

fringe 

branching and constrictions Growing on upper shore in crevices 


42

Ceramium nodulosum 

Ceramium 

shuttleworthanium 

Ceramium sp. 

Chondrus crispus 


Cryptopleura ramosa 

Cystoclonium purpureum 

Delesseria sanguinea 

Dilsea carnosa 

Dumontia contorta 

Erythrotrichia carnea 

Furcellaria lumbricalis 

Gastroclonium ovatum 

Gelidium sp. 

Gracilaria gracilis 

Halurus equisetifolius 


Filamentous, variously branched, dark pink; 

may appear banded 

Filamentous, numerously branched, 

red/dark pink with spines; may appear 

banded 

Filamentous, numerously branched, dark 

pink may appear banded 

Tough, flat, with wide wedge shape frond, 

dichotomous branching & stipe; highly 

variable form and easy to confuse with 

Mastocarpus 

Calcareous and jointed with bone like 

structure, light pink in colour 

Blade wide, foliose, thin and leafy with 

veins, and frilly blade edges 

Firm, cartilaginous, straggly, variously 

branched, long with claw holdfast 

Foliose, delicate, resembles thin beech leaf 

with distinct midrib & veins, ruffled edge 

Tough and leathery with wedge shaped 

divisions, branching from base 

Soft, hollow sometimes gelatinous and 

slimy, limited branching 

Fine unbranched filaments, epiphytic and 

microscopic 

Tough, cartilaginous, cylindrical frond, 

dichotomous branching, claw holdfast 

Fleshy, cylindrical branches with small 

bundles at tips with base constricted 

Tough, slightly cartilaginous, irregular 

branching, broad flattened tips but 

cylindrical lower section 

Long, straggly, cartilaginous and firm, 

irregular branching and pointed tips 

Filamentous with whorled branching 

resembling bottle brush 

Filamentous, fine, hair-like, highly 

branched, bright pink 

Found growing throughout the littoral 

region within a variety of habitats 


region within a variety of habitats, often 

found on mussels 



Grows throughout the littoral on a variety 

of surfaces 

Found growing throughout littoral region 

within a variety of habitats, particularly 

rockpools 

Grows in the lower littoral/sublittoral 

fringe 

Found on the mid to lower shore usually 

within wide shallow rockpools 


fringe 


fringe 

More common found in the mid to upper 

littoral in shallow rockpools 

Grows epiphytically on variety of 

Polysiphonia and Ceramium sp. throughout 

littoral 

Found in sandy bottom rockpools usually 

in mid to lower littoral regions 

More common found in the mid to upper 

littoral in shallow rockpools 

Found on mid to lower shore on rock 

surfaces, crevices and overhangs often 

forming turfs or mats 

Found in the mid and lower littoral within 

pools and on open rock surfaces 

Grows in the mid to lower littoral 

particularly in rockpools and damp 

overhangs 

Grows in the mid to lower littoral 

particularly in rockpools and damp 

overhangs 


43

Heterosiphonia plumosa 

Fine filamentous, with numerous small 

branches appearing tufted 

Found throughout the littoral region within 

a variety of habitats but mainly rockpools 

Hildenbrandia rubra Deep red staining on the rock surface Found on various hard substrates and rocks 

Hypoglossum 

hypoglossoides 

Lomentaria articulata 


Mastocarpus stellatus 

Melobesia membranacea 

Membranoptera alata 


Odonthalia dentata 

Osmundea hybrida 

Osmundea pinnatifida 

Palmaria palmata 

Phycodrys rubens 

Phyllophora sp. 

Plocamium cartilagineum 


Polyides rotundus 

Foliose, delicate, branched with distinct 

midrib from which bladelets arise, pointed, 

small, narrow fronds 

Pink, bead like, fleshy and numerously 

branched 

Pink, bead like, fleshy and numerously 

branched in single plane, appearing flat 

In-rolled gutter-like frond, tough and 

cartilaginous; variable form 

Calcareous small spots or stains, 

microscopic and epiphytic 

Foliose, delicate, branched with distinct 

midrib narrow, small, rounded fronds, 

branching from outer frond 

Gelatinous, squashy, slippery and elastic 

with few branches 

Narrow, slightly foliose but tough frond, 

regular alternate branching; tooth-like 

Thick, fleshy, alternate or opposite 

branching in all planes 

Thick, fleshy, alternate branching in single 

plane, appears flattened 

Tough but fleshy and floppy, divided blade 

with bladelets 

Foliose, delicate, resembles thin oak leaf 

with distinct midrib & veins, serrated edge 

Blade foliose, thin and leafy with faint 

midrib & veins, cylindrical stipe 

Fine, filiform and delicate with comb-like 

branching, very pink 

Fine, filamentous, delicate short and long 

branches not regularly alternate, dark purple 

or brown 

Tough, cartilaginous, cylindrical frond, 

dichotomous branching, disc holdfast 

Found mainly on the lower shore often 

with other red in the littoral fringe 

Found in overhangs and crevices in 

amongst turf formers on mid and lower 

shore 



shore 

Grows throughout the littoral on a variety 

of surfaces easy to confuse with Chondrus 

Grows epiphytically on a variety of 

filamentous species 



shore 

Found mainly in the mid littoral on open 

rock surfaces or in shallow pools on 

southern/western shores 


fringe 

Found in a variety of habitats on mid and 

lower shore may be mingled with 

mats/turfs 

Found in a variety of habitats on mid and 

lower shore may be mingled with 

mats/turfs 


fringe and can be very abundant 


fringe 


fringe 


fringe and sometimes mid-littoral pools 



shore 

Found in sandy bottom rockpools usually 

in mid to lower littoral regions 


44

Polysiphonia fucoides 

Polysiphonia lanosa 

Polysiphonia sp. 

Porphyra leucosticta 

Porphyra umbilicalis 


Rhodomela confervoides 


Filamentous, pink to dark brown/black, Found growing throughout the littoral 

variously branched 


Filamentous, coarse black and slightly Found growing on Ascophyllum nodosum 

tufted 

only on mid to upper shore 

Filamentous, dark brown/black, variously Found growing throughout the littoral 

branched 


Thin, foliose, unbranched blade, 

membranous, attached to Fucus sp. 

Thin, foliose, wide unbranched blade, 

Grows on Fucus throughout the littoral 

membranous with central attachment Generally found throughout the littoral 

Fine, filamentous, very delicate with Found in overhangs and crevices in 

opposite long and short branches which are amongst turf formers on mid and lower 

regularly alternate; red in colour 

shore 

Firm, cartilaginous, straggly, variously Found on the mid to lower shore usually 

branched, long with disc holdfast 

within wide shallow rockpools 

Fine, filamentous, short tufted, unbranched Found on sand covered rocks as a sand 

and forming a mat 

binding species throughout littoral 


45

SPECIES DESCRIPTIONS AND IMAGES 

The next section describes each of the species within the reduced species list giving 

one or more photographs where possible. It should be noted that this guide should be 

used in conjunction with other identification guides such as those listed below to 

enable more accurate identification. 

During sampling it is likely that other specimens of benthic macroalgae not within the 

reduced species list will be collected and it is essential that these are not confused 

with the required species as these may inappropriately inflate the total number of 

species recorded. Where this is likely to be problematic additional species of 

confusion have been noted in the descriptive text. Unfortunately this guide only 

covers those species within the reduced species list, therefore further comparisons 

may require those additional identification guides recommended. It is also possible for 

many species to exhibit several morphological forms depending on the local 

environmental factors or time of year. Some specimens collected may be old or tatty 

and may not display their true form so this needs to be taken into account whilst 

comparing specimens with guide photos. Many species may also look 

morphologically similar in the field such as some of the fine filamentous forms 

therefore field photographs for such specimens may be indistinguishable. 

Additional recommended identification guides 

Purpose 

General 

seaweed 

species 

General 

Rhodophyta 

species 

General 

Phaeophyta 

species 

General 

Chlorophyta 

species 

Title 

Author( 

s) 

A Hand Book of the British seaweeds Newton, 1931 

Seaweed of the British Isles. Vol. 1 part 1 Dixon & Irvine, 1977 

Seaweed of the British Isles. Vol. 1 part 3A Maggs & Hommersand, 1993 

Seaweed of the British Isles. Vol. 1 Part 2A Irvine, 1983 

Seaweed of the British Isles. Vol. 1 Part 2B Irvine & Chamberlain, 1994 

Unpublished key to red seaweed Ian Tittley (NHM, pers comm) 

A field key to the British red seaweeds Hiscock, 1986 

A field key to the British brown seaweeds Hiscock, 1979 

Seaweeds of the British Isles. Vol. 2 Burrows, 1991 

46

Blidingia sp. 

This is a tubular and foliose species, although due to its small 

size it often appears filamentous in form. It is found growing at 

the top of the shore often in mat form, covering large boulders. 

It is also found growing epiphytically on Fucus species 

although microscopic examination is required to distinguish it 

from Ulothrix species which are also known to grow on Fucus 

sp. The cells are generally small and cellular contents may be 

hard to distinguish but this characteristic may be used to 

separate it from Enteromorpha sp. where cells are larger. It 

has a round basal discoid holdfast unlike Enteromorpha which 

has rhizoidal cells. Some specimens also appear to have a 

slight margin where the outer filament walls seem thicker. 

Blidingia is also common in estuaries and on artificial 

structures e.g. bridge supports. 

Cells usually less than 

10um, so do not appear to 

have easily distinguishable 

contents 

Blidingia growing on small boulders 

Cellular arrangement of 

Blidingia showing thickened 

filament walls and small size 

of cells


This is a coenocytic species in which there are no cellular 

divisions and the cell contents move freely throughout the 

filaments. The filaments/branches are regularly arranged in 

a single plane to form a delicate feather-like plant. Base of 

branches may be slightly constricted. May be hard to 

locate as it is generally present on the shore in low 

abundance, but can be found attached to the sides of 

variously sized rockpools. It may be easily distinguished 

from other green filamentous algae due to its fine delicate 

appearance. Not to be confused with Vaucheria which 

although not visibly similar is also coenocytic. 

Natural habitat of 

Bryopsis in rockpools 

Feather-like appearance 

of Bryopsis 

Coenocytic filaments with no cell 

divisions and constricted at branch base

Chaetomorpha linum 

This is an unbranched filament with a reticulate or 

network-like chloroplast which generally fills the 

whole cell with colour with numerous pyrenoids 

present within each cells. The cells tend to be as 

long as broad or slightly longer and are often 

barrel shaped. This species of Chaetomorpha has 

a filament width of between 100-300um. It takes 

the appearance of thick, tough, wiry floating 

masses, like green garden wire or wire wool and is 

located on the upper or mid shore on open rock 

surfaces or in shallow rockpools and often in 

dense clumps. It may form mat-like blooms on soft 

sediments in estuaries 

Dense clumps of Chaetomorpha 

linum appearing as tough wiry 

masses 

Large cells filled with reticulate 

chloroplast

Chaetomorpha mediterranea 

This is an unbranched filament with a reticulate or 

network-like chloroplast which generally fills the 

whole cell with colour and numerous pyrenoids. 

The cells tend to be as long as broad or slightly 

longer and barrel shaped. This species of 

Chaetomorpha has a filament width of

Chaetomorpha melagonium 

This is an unbranched filament with a reticulate or network-like 

chloroplast which generally fills the whole cell with colour and 

numerous pyrenoids. The cells tend to be as long as broad or 

slightly longer and barrel shaped. This species of 

Chaetomorpha has cell size of up to 1mm and the cells may 

be visible to the naked eye giving a beaded appearance. It 

exists as a solitary, erect filament, often quite firm and coarse 

in texture, and is found in the bottom of rockpools in amongst 

numerous other algae. Desiccation of this species causes it to 

lose its rigidity, and it will subsequently collapse. May be found 

with epiphytes attached to the outer cell walls. 

Presence of epiphytes 

on filament 

Large barrel shaped 

cells filled with 

reticulate chloroplast 

Solitary, erect filament 

found in amongst Corallina 

and Cladophora sp. in 

rockpool

Cladophora sp. 

Highly branched filamentous species with a dense 

reticulate chloroplast with cells appearing uniformly 

green and with numerous pyrenoids visible on staining. 

Found as tufts or bushy plants throughout the intertidal 

but primarily on the upper and mid shore on open rock 

surfaces and within rockpools. 

Cladophora albida – consisting 

of very fine and narrow filaments 

generally less than 20um wide. It 

is delicate, fluffy and light green in 

colour with rounded apical cells 

and often epiphytic. 

Cladophora sericea – consisting of 

broad filaments >80um but lighter 

green in colour and less densely 

tufted/branched. Branching various 

including dichotomous and secund or 

comb-like with narrowing apices. 

Cladophora rupestris – consisting of 

broad filaments >80um as dark green 

and course, stiff, dense tufts with 

clear multidichotomous branching and 

may have 5-6 branches arising from 1 

cell. Often supporting epiphytes.

Enteromorpha sp. 

A tubular plant which can appear flattened and 

foliose. just one cell thick. Cells generally 

>12um wide with parietal chloroplast and 

pyrenoids varying in number and size. 

Morphology varies considerably between 

species ranging from highly branched to 

unbranched, regular and irregular cell 

arrangements, compressed, ribbon-like and 

bulbous forms. Generally bright green in colour 

and found throughout the intertidal area but 

most common on the upper shore particularly in 

upper shore rockpools around areas of 

freshwater input and on areas of soft sediment. 

Cells may be irregularly 

or regularly arranged 

Plants may appear highly 

branched, ribbon-like and 

bulbous 

Pyrenoids may be 

numerous and small 

or single and large

Monostroma grevillei 

A foliose plant only one layer of cells thick, very 

pale green in colour, very thin and membranous 

and quite easily torn. Cells with parietal 

chloroplast and with one to several pyrenoids, 

cells tend to be regularly arranged in packs of two 

or four. Broad, flat, fine and delicate leaf-like 

morphology with central basal attachment. 

Occurs in rockpools mainly on the upper shore 

and are most commonly present during the spring 

months 

Cells arranged in packs of 

two or four 

Thallus very fine, almost 

transparent with open flat form 

arising from the splitting of a 

primary tubular structure with 

central holdfast

Rhizoclonium tortuosum 

Plant consists of long unbranched filaments with cells 

generally much longer than broad, mean cell 

diameter 10-30um but up to 100um long and 40um 

wide, with reticulate chloroplast and numerous 

pyrenoids. Rhizoidal branches of between 1 and 3 

cells long may be present, often referred to as ‘false 

branching’. Rhizoclonium tends to form dense, 

entangled mats or turfs on upper shore rocks very 

close to the terrestrial boundary, found on large flat 

areas and around areas of freshwater influence, in 

estuaries and salt marshes. It requires microscopic 

identification to distinguish form other mat forming 

filamentous green algae. 

Filament consisting of long 

slender cells with ‘false’ or 

rhizoidal branching present. 

Filament forming a prostrate 

system appearing as mat 

particularly on upper shore 

flat surfaces


Highly branched filamentous and tufted in 

morphology and bright green in colour. Cells longer 

than broad with reticulate chloroplast consisting of a 

fine non-dense network of fibrils, which are clearly 

visible under the microscope, apical cells often 

slightly bulbous and conspicuous. Fine reticulate 

chloroplast also makes the numerous pyrenoids 

easily distinguishable. Branches may be straight, 

downward growing and rhizoidal or hook shaped 

which may lead to filaments become entangled and 

rope-like. Often found in moist overhangs within 

turfs of other green and red algae on the mid shore 

region. May be confused superficially with 

Cladophora sp. 

Pyrenoids highly 

visible as green 

discs 

Branching and filaments may be straight or 

in-rolled forming hooks 

Plants are often highly branched and filaments 

may become entangled forming ropes

Sykidion moorei 

Plant consisting of a single cell embedded 

between the mucilage walls of Blidingia 

species fronds. Easily distinguished from 

Blidingia cells as they are much larger.

Ulothrix sp. 

Plant consisting of long unbranched filaments 

bright green in colour. Cells usually much shorter 

than broad or may be equal length and breadth, 

approximately 10-30um, with a single band 

shaped parietal chloroplast covering about ¾ of 

the inner cell wall, pyrenoids (one to many) often 

visible within the chloroplast. Ulothrix present in a 

number of morphologies with wide or narrow 

filament wall and filament width variable and as 

straight or curled filaments often as a result of 

reproductive bodies. Plants may be found in turfs 

on rock surfaces or commonly found growing 

epiphytically on Fucus species where microscopic 

identification is required to distinguish from 

Blidingia and other filamentous species known to 

grow on Fucus. May be confused with Urospora 

sp. which have larger barrel shaped cells. 

Filaments either straight or curled up 

forms may also be found together 

Filaments with thin or 

thick walls, cells wide 

and flat or broad and 

pyrenoids often clearly 

Ulothrix often found 

visible 

growing on Fucus sp.

Ulva lactuca 

A flat foliose plant two layers of cells thick 

which can be seen by focusing up and down 

under the microscope. Cells of various shapes 

and sizes with no regular arrangement, 

chloroplasts parietal sometimes filling the 

whole cell other times appearing more band 

shaped with one to several pyrenoids per cell. 

Plant found throughout the littoral zone, but 

commonly located on the lower littoral. 

Morphological form a tough bright green broad 

frond resembling a lettuce leaf. Other species 

of Ulva may be found but U. lactuca is the 

most common. 

Chloroplast filling 

the whole cell 

Distinct two layers of 

cells 

Ulva found in natural habitat on the 

lower shore mixed in with numerous 

other brown and red species

Alaria esculente 

Plant consisting of a distinct thick flattened 

and leathery midrib and cylindrical stipe 

leading to a claw shaped holdfast. The lamina 

tends to be slightly wavy, membranous and is 

often quite torn and tatty due to its slightly 

delicate consistency. A large plant often found 

growing up to 5m long and generally located 

in the lower littoral and sublittoral but may be 

found within lower shore deep rockpools. 

Light brown/tan in colour. 

Claw-like holdfast extending to 

cylindrical thick stipe 

Distinct midrib with delicate and torn lamina 

often feather-like within a rockpool, and on open 

hard substrate looking slightly membranous


Frond very long, branched and strap-like with 

single large ovoid bladders present in 

intervals along the length of the frond, which 

may be between 1 and 5 cm long. If present 

receptacles are found on stalks within 

marginal notches. Fronds can grow up to 

150cm long and may be found in great 

abundance particularly on very sheltered 

shores where they can cover vast areas of 

the littoral area. Stunted forms also exist but 

are generally found on more exposed 

shores. Often greeny brown in colour 

Ascophyllum often very 

abundant on sheltered shores 

Large air bladders at 

intervals along the main 

frond, presence of 

Polysiphonia lanosa also a 

characteristic of 

Ascophyllum 

Stunted form

Asperococcus fistulosus 

Fronds irregular in width, often slightly 

crinkled and randomly constricted. Plant 

appears tubular, hollow and often bulbous 

looking, quite delicate and may be easily torn 

and may grow up to 30cm long, often 

resembles a tough brown Enteromorpha. 

Branching very limited and tends to be 

restricted to the base of the plant only. 

Clusters of reproductive bodies appearing as 

small scattered spots. Generally located in 

rockpools throughout the littoral but most 

commonly found in the mid littoral. Not to be 

confused with Scytosiphon sp. 

Cells of Asperococcus 

as seen under high 

magnification 

Sori (reproductive 

bodies) appearing as 

spots along the frond 

Asperococcus growing in a rockpool 

Plant showing limited branching

Chordaria flagelliformis 

Plant often very fine, delicate, slightly 

gelatinous and light brown in colour. 

Branches very irregular but numerous and 

can appear as thick crinkly filaments or 

filiform and growing up to 70cm long. 

Filaments may have an all-over covering 

of fine hairs. Found most frequently in the 

mid littoral area within wide shallow 

rockpools. May be confused with 

Dictyosiphon sp. 

Chorda Filum 

Plant completely unbranched, long, cylindrical 

and resembling a bootlace, may be quite tough 

but elastic and can grow up to 8m long. Found 

on the lower littoral fringe and within wide 

shallow and often sandy bottomed rockpools in 

the mid littoral.

Cladostephus spongiosus 

This is a course, stiff species and variously 

branched, consisting of numerous tiny 

branchlets which are arranged around the 

main filaments/axis in a ring formation 

(whorled) causing dense tufting and 

resembling a bottle brush. This plant grows 

in the mid and lower littoral particularly on 

overhangs and mixed in with other turf 

forming species and can grow up to 25cm 

long. 

Whorled arrangement of branchlets 

covering the whole plant 

Plant displaying course and wiry 

consistency and with limited branchlets 

on the lower/basal filaments 

Plant in its natural 

habitat in amongst 

other algae as a 

dense tuft


Frond often quite narrow, generally 

less than 2mm, flattened, coarse and 

reddy brown in colour. The long main 

axis is highly and regularly alternately 

branched and can grow up to 180cm. 

Side branches may be quite long but 

in older plants branchlets appears 

short, spine-like and look serrated. 

Found most frequently in the lower 

littoral particularly in sandy or 

unstable substrate bottomed pools 

Desmarestia in its natural 

habitat, with a distinct 

serrated appearance in 

older plants and with the 

long main axis clothed in 

long branchlets as seen in 

younger plants 

Dictyosiphon foeniculaceus 

Plant quite fine and delicate and light 

brown in colour. Branches very irregular 

and generally from main axis appearing 

as straight thick filaments or filiform and 

growing up to 70cm long. Filaments 

often have an all-over covering of fine 

hairs. Found most frequently in the mid 

littoral area within wide shallow 

rockpools often with sandy bottom. May 

be confused with Chordaria sp. 

Dictyosiphon in natural habitat

Dictyota dichotoma 

Frond quite thin and foliose, generally flat 

but may become spiralled in narrow 

fronded specimens, with frond width 

varying considerably between plants. Plant 

exhibits regular dichotomous branching 

which may be quite prolific. Frond tips 

usually bifid (divided into 2) and with 

prominent and large apical cells. Tend to 

be located in rockpools in the mid and 

lower littoral and often on sandy substrate 

Distinct dichotomous 

branching 

Dictyota in natural 

rockpool habitat 

Frond tips showing bifid characteristic 

and prominent apical cells

Ectocarpus sp. 

Fine filamentous form with no distinct main 

axis, often confused with other filamentous 

brown species such as Giffordia and 

Pilayella. Profusely branched appearing 

hair-like, branches can sometimes be 

secund and opposite but generally 

irregular. Characterised by its ribbon 

shaped chloroplasts and long spindle 

shaped sporangia. Found growing within 

mixed mats on open hard substrates and 

epiphytically on Fucus or other large algae. 

Requires microscopic identification. 

Growing on sandy substrate attached 

to Enteromorpha but is also found 

growing on hard substrate 

Ribbon shaped chloroplasts 

Long spindle shaped sporangia 

extending from small branches or 

stalks, some species may have 

shorter fatter sporangia


Fine filamentous form, unbranched with 

cells generally as long as broad. 

Characteristically found growing on Fucus 

sp. as little tufts appearing brush-like or 

densely covering the whole frond as very 

fine hairs, often with a lump at the base of 

each tuft. Commonly found throughout the 

whole littoral but does depend on the 

presence of Fucus 

Simple unbranched 

filaments 

Growing as short 

sparse tufts on 

Fucus 

Densely covering Fucus as fine hairs

Fucus sp. 

Plants tough, cartilaginous and not 

easily torn, with midrib and greeny/ 

brown in colour with three more 

common species 

Fucus serratus – characterised 

by its serrated edge and long flat 

reproductive tips, found on the 

lower littoral area of the shore. 

Fucus vesiculosus – 

characterised by the presence of 

pairs of air bladders or vesicles 

(bladders are occasionally known 

to be absent), reproductive tips 

tend to be large and swollen, 

found in the mid littoral. 

Fucus spiralis – 

characterised by its 

spiralled frond, 

swollen reproductive 

tips with distinct 

sterile rim of cells, 

found in the upper 

zone of the shore


Plant tough and cartilaginous with 

pod like air bladders divided 

internally by cross-walls. Exhibits 

regular alternate branching with a 

‘zig-zag’ appearance. Generally 

found within mid to deep rockpools 

in the mid to lower littoral zones 

Himanthalia elongata 

Plant a long tough, 

cartilaginous strap shaped 

frond, characterised by its 

large button shaped and 

slightly stalked attachment 

structure. Not highly branched 

but distinctly dichotomous with 

branches growing up to 

150cm long, and found in the 

lower littoral on rock outcrops 

or large shelves

Laminaria sp. 

Thick leathery, very tough and 

cartilaginous frond with thick 

cylindrical and distinct stipe and 

claw-like holdfast. 

Found growing in the lower 

littoral fringe and subtidally often 

forming dense kelp beds. 

Laminaria digitata – stipe 

flexible and smooth only 

stands upright in water, 

with broad split frond 

appearing finger-like 

growing up to 2m long 

Laminaria saccharina – 

characterised by its crinkly, wavy 

edge and undivided blade growing 

up to 4m 

Laminaria hyperborea – Rough stipe usually covered 

with numerous red algal epiphytes, stipe very stiff and 

stands upright with very broad finger-like split lamina 

growing up to 3m long.

Leathesia difformis 

Plant spherical, bulbous and hollow, gelatinous 

and can be easily squashed, but slightly more 

solid when young. Often found growing on other 

algae particularly Osmundea and Corallina but 

may also form dense patches on open rock 

surfaces and on the sides of rockpools. Found 

throughout the mid and lower littoral areas and 

can grow up to 5cm long/wide. Not to be 

confused with Colpomenia sp. 

Plant bulbous 

and hollow 

Plant made up of 

numerous filaments 

with reproductive 

bodies appearing as 

dark spherical patches 

Growing on solid substrate 

and within crevices, and 

found in rockpools

Litosiphon laminariae 

Epiphytic plant growing as fine 

multiseriate filaments on the fronds 

of Alaria. Found as small dark tufts 

and located in the lower littoral and 

sublittoral. Not to be confused with 

other similar filamentous species. 

Pelvetia canaliculata 

Frond characteristically in-rolled 

forming a central channel, 

although quite limp they are 

tough and slightly elastic with 

swollen reproductive frond tips. 

Found growing in dense tufts on 

the upper region of the shore 

extending to up to 15cm long. 

Often found growing out of 

cracks or crevices and may be 

greeny brown in colour or 

sometimes slightly yellow. 

Natural morphology 

and habitat of Pelvetia 

Multiseriate filaments of Litosiphon

Petalonia fascia 

Frond thin, membranous and foliose, but 

also quite tough, strong and elastic. Frond 

appearing as a simple undivided ribbon 

shape which narrows to a short stipe at 

the base, branching only occurs from the 

base. Frond can vary but can be wavy and 

crinkly at the edges growing up to 30cm 

long, can be mistaken for juvenile 

Laminaria plants. Found in rockpools 

particularly shallow ones with a soft 

substrate. 

Plant in sandy 

bottomed rockpool Frond of Petalonia with 

reproductive bides shown 

as dark small patches 

Plant only branched from 

base with simple 

attachment structure 

Cells of Petalonia as seen under greater 

magnification showing regular arrangement 

and discoid chloroplasts

Pilayella littoralis 

Fine filamentous form with no distinct main axis, often confused with 

other filamentous brown species such as Ectocarpus and Pilayella. 

Profusely branched appearing hair-like, branches can sometimes be 

secund and opposite but generally irregular. Characterised by its 

discoid shaped chloroplasts and intercalary sporangia appearing as 

swollen cells within the filaments throughout the plant. Found growing 

within mixed mats on open hard or soft substrates and epiphytically 

on Fucus or other large algae. Requires microscopic identification. 

Growing on rock surfaces 

and may also be found 

growing along side 

Enteromorpha on sandy 

substrate 

Intercalary sporangia 

used to distinguish 

from other brown 

filamentous species

Sacchoriza polyschides 

Thick, leathery, tough and cartilaginous, with 

thick flat stipe extending from bulbous and 

distinct base. Base of stipe with ribbon-like 

growths protruding from sides. Lamina large, 

broad and flat which is split to form several 

blades. Found growing in the lower littoral and 

subtidal regions of the shore 

Bulb-like base with 

crinkly sides to 

lower stipes 

Ralfsia sp. 

Dark brown/black crust found growing 

throughout the littoral zone on limpets and 

open rock surfaces, no erect system present.

Scytosiphon lomentaria 

Plant characterised by its regular pronounced 

constrictions present down the length of the frond 

giving the appearance of a string of sausages. 

Frond generally quite narrow and hollow and 

unbranched with frond developing from main base 

only, which is a distinct disc. Found growing 

throughout the littoral on both open hard surfaces 

with other algal species and within sandy 

bottomed rockpools. Not to be confused with 

Asperococcus sp. 

Scytosiphon found growing in amongst 

Enteromorpha on hard substrate 

Plant branched from base only with 

characteristic constrictions at intervals 

Discoid basal attachment

Sphacelaria sp. 

Plant small, usually less than 2-3cm long, tufted and stiff 

retaining its shaped even in water. Consisting of numerous 

multiseriate filaments which may be 2 to many cells wide, 

branching numerous and is generally irregular except in 

ultimate branches where it may become pinnate and opposite 

or alternate. Characterised by a prominent large and slightly 

bulbous apical cell and the presence of propagules which 

detach from filaments during reproduction. Found growing 

within mixed turfs in overhangs and epiphytically on Corallina. 

Prominent rounded 

apical cells 

Reproductive 

structures exist 

as propagules 

Densely tufted 

and stiff 

Branching pinnate and alternate 

or opposite

Spongonema tomentosum 

Fine and filamentous and tangled into 

distinct woolly cords due to curled hooklike 

branches and generally limp, floppy 

and hair like. Highly and irregularly 

branched and consisting of uniseriate 

filaments but requires microscopic 

identification to distinguish from 

Ectocarpus and Pilayella. Commonly 

found attached to Fucus sp. throughout 

the littoral, may also be found in turfs 

and within rockpools. 

Characteristic 

hooked ultimate 

branches can be 

used to distinguish 

from other brown 

filamentous species 

Filaments form 

tangled woolly 

cords and attach 

to Fucus sp. 

Filaments 

uniseriate and 

numerously and 

irregularly 

branched

Aglaothamnion/ Callithamnion 

The form of these two genera are generally very 

fine and delicate consisting of numerously 

branched uniseriate filaments (single row of 

cells). Plants are often quite bushy and spongy 

due to the covering of numerous branchlets or 

ramuli extending from the main axis. Branching 

patterns can vary from regularly alternate to 

subdichotomous and dichotomous with both 

rounded and pointed apices. Cells are longer than 

broad and are often bone shaped. They tend to 

be quite small and are often found living amongst 

turfs in overhangs and attached to mussels, or 

epiphytically on a variety of algae. Aglaothamnion 

spp. tend to have a single visible nucleus where 

as Callithamnion spp. are known to have several 

nuclei. 

Cells of Callithamnion sp. clearly 

showing the numerous nuclei 

present as light pink spots. 

Aglaothamnion species only have 

one nucleus per cells. 

The variety of forms of Aglaothamnion 

and Callithamnion and in its natural turf 

forming habitat and showing its various 

branching patterns

Ahnfeltia plicata 

Plant completely cylindrical 

throughout, very coarse, black and 

wiry with narrow fronds of 0.5mm or 

less. Branching is highly irregular with 

branches very variable in length but 

growing up to 15cm long. It is tolerant 

of sand cover and tends to be located 

in sandy bottomed pools attaching by 

a discoid holdfast. It is found in the 

lower littoral most commonly in 

rockpools. 


Small microscopic plant consisting of 

uniseriate filaments. Cells tends to be 

longer than broad and are completely 

filled with a dense reticulate chloroplast 

resulting in a dark pink colour. Branching 

is minimal and completely irregular. 

Plants tend to be very tangled and are 

located within turfs forming a moss on 

overhangs and general dark damp areas 

throughout the littoral. Not to be confused 

with Rhodothamniella floridula. 

Typical black wiry form of Ahnfeltia with 

close up of cylindrical fronds 

Long, narrow cells of 

A. purpurea with dense 

reticulate chloroplast 

Uniseriate filaments of 

A. purpurea found in 

tangled mats or turfs

Audouinella sp. 

Other Audouinella species tend to be much smaller and only a few cells in length and require a 

microscope just to locate them. They grow epiphytically on a variety of other algal species e.g. A. 

davesii is commonly found on the fronds of Palmaria palmata but may also be found within hydroids 

and can live throughout the littoral. The cell size and shape may vary as can the chloroplast but it rarely 

fills the whole cell as with A. purpurea. Plants tend to be short and variously branched growing from 

either a unicellular or multicellular base. Plants can also be erect, prostrate or a combination of the two. 

They can be differentiated from A. purpurea by their microscopic size. 

Audouinella davesii found growing 

on the frond of Enteromorpha sp. 

A number of Audouinella 

sp. are often found in 

hydroids 

Audouinella sp. showing unbranched form growing 

from a multicellular base and highly branched form.

Calcareous encrusters 

Calcareous encrusters incorporate a number of 

Species from various genera including 

Lithophyllum, Lithothamnion, Phymatolithon, and 

Mesophyllum. They are very distinct forming a hard 

coating over rock surfaces and occasionally on the 

fronds of other algae such as Titanoderma which is 

often found on Polyides. They grow in a variety of 

colours ranging from light to dark pink, deep red 

and purple and may also be slightly speckled with 

the edges often bleaching. Not to be confused with 

the basal portion of Corallina sp. They are found 

throughout the littoral and sublittoral appearing in a 

variety of forms including a smooth shiny surface, 

lumpy, knobbly crusts, with smooth edges or highly 

convoluted ridges. Very common.

Callophyllis laciniata 

This is a foliose species and tends to be very thin, 

membranous, soft and fleshy. Fronds are wide and often 

much divided or split into broad fan shaped sections and 

are bright pink in colour. The edges may be slightly frilly 

and reproductive bodies are found in the slightly frilly 

edges of the fronds which often form bladelets.. Found in 

the lower littoral and sublittoral fringe frequently located 

on kelp stipes and holdfasts. May be distinguished from 

Cryptopleura sp. by the absence of a midrib or veins. 

Catenella in natural 

habitat and showing 

its variable form with 

irregular constrictions 

Foliose nature of Callophyllis with 

reproductive bodies 


Plant is small, soft and slightly squashy and 

only grow to 2cm long. It has very irregular 

branching and is constricted at irregular 

intervals along the plant. It is generally filiform 

but segments may be cylindrical and or very 

flattened often appearing slightly fleshy. It is 

found most commonly in the upper littoral 

area but may be found in the mid littoral. Not 

to be confused with Gelidium sp.

Ceramium nodulosum 

This is a highly branched filamentous species, often 

characterised by its banded or striped appearance which may 

be visible with the naked eye. Although the main axis consists 

of a single row of cells there is a covering of small cells which 

become particularly dense at the junction between axial cells, 

which results in the banding. The branching pattern is usually 

dichotomous or subdichotomous where terminal branches 

may be tightly in-rolled. Fine hairs may also be present along 

the full length of the filament but these are not to be confused 

with spines. Although there is a number of Ceramium spp. 

this is the most common and can be found throughout the 

littoral within rockpools, on open rock surfaces and growing 

epiphytically on a range of red and brown species. The form 

can be quite variable. 

Single row of axial cells 

Dense covering of small cells 

between axial cells and 

strongly in-rolled apices 

Highly and dichotomously 

branched 

C. nodulosum filament with 

fruiting bodies and obvious 

banding

Ceramium shuttleworthianum 

This is a highly branched filamentous 

species with the main axis consisting of a 

single row of cells. The covering of small 

cells is often incomplete resulting in a 

clearly banded effect. This species is 

mainly characterised by the presence of 

multicellular spines on the outside of each 

node and the strongly hooked or in-rolled 

apices. The branching pattern is regularly 

dichotomous and is often densely matted. 

This species of Ceramium is found in the 

mid and lower littoral on rocks, mussels, 

other algae and within overhangs and 

crevices. 

Ceramium spp. 

Species displaying slight variations of 

the characteristics of C. nodulosum and 

C. shuttleworthianum. Some species 

may be completely covered with small 

cells (corticate) other may have very 

distinct banding with cells present at 

the nodes only. Spines may be present 

or absent, the spines may be 

multicellular or single celled and may 

whorled, dense or sparse. 

Strongly hooked apices with 

spines on outside of nodes 

Spines greater than 

one cell in length and 

with multicellular base 

Banding visible with 

the naked eye 

Other Ceramium species may be spined, highly 

corticated or highly banded

Chondrus crispus 

This species is cartilaginous, often quite tough 

and slightly elastic, with frond displaying 

regularly dichotomous divisions. Fronds are 

completely flat and may be quite wide and 

wedge shaped. The stipe is also completely 

flat and much narrow than the main frond. 

Colour may vary from light brown and yellow 

to deep red or purple. Found throughout the 

littoral zone on a variety of surfaces, very 

common. Not to be confused with 

Mastocarpus stellatus which has a slightly 

channelled frond. May be fluorescent in water. 


Plant consisting of erect jointed calcareous 

structure often appearing bone-like. 

Branching pattern regularly opposite. Pink 

in colour often turning completely or 

partially (just the tips) white due to 

bleaching. Some fronds may appear 

elongate where as others may be more fan 

shaped. Found in the mid littoral through to 

the sublittoral most commonly within 

rockpools but may be found on open rock 

surfaces. 

Chondrus in its natural 

habitat in a range of 

colours and showing 

its narrow stipe and 

flat dichotomous frond 

Corallina found 

commonly in 

rockpools consisting 

of a calcareous bonelike 

frond light pink 

in colour.

Cryptopleura ramosa 

Plant is thin, membranous, foliose and quite delicate. It is 

light pink and often iridescent. The main frond is divided 

into wide sections, although the general shape can be 

highly variable with narrow long or broad fronds. 

Microscopic veins are present but there is no distinct 

midrib. Apices often rounded with a slightly frilly or ruffled 

edge within which tetraspores may be present, branches 

may also be slightly hooked or curled. This species can 

grow up to 2.5 cm wide and 20 cm long. It is found in the 

lower littoral generally within pools attaching to rock, kelp 

stipes and other algae via a short stipe and disc holdfast. 

Plant showing broad frond with ruffled edges 

Frond with microscopic veins 

present throughout and 

tetraspores located on the outer 

edges of the plant 

Plant displaying highly branched form with 

narrow delicate fronds and minimal stipe

Cystoclonium purpureum 

This is a filiform plant often with a distinct main 

axis which may be up to 2 mm wide. It is highly 

and irregularly branched, growing up to 60 cm 

long and can appear quite straggly. This species 

is often distinguished from similar species such 

as Rhodomela sp. by its distinct claw-like 

branched holdfast. Cystocarps can appear as 

swellings within the smaller branches. It is found 

in the mid to lower littoral and sublittoral fringe, 

generally located within rockpools and may be 

browny red or purple in colour. 

Delesseria sanguinea 

Plant with distinct and uninterrupted midrib and 

side veins. Very thin, foliose, membranous and 

delicate, plant with limited branching generally 

occurring at the base and arising from a main 

thick stipe. Fronds long and broad growing up 

to 40 com long with edges appearing ruffled 

often resembling elongated beech leaves. 

Pinky red in colour it is found in the lower 

littoral and sublittoral fringe and within deep 

lower littoral rockpools, may be found attached 

to kelp stipes. Not to be confused with 

Phycodrys rubens. 

Delesseria with distinct 

leaf like appearance due 

to thick midrib and 

veins 

General appearance of 

Cystoclonium with claw-like 

holdfast, cellular structure and 

presence of cystocarps 

Branching of Delesseria 

from main stipe near 

base only

Dilsea carnosa 

Plants thick (up to 1 mm), tough and leathery but 

slightly elastic and may reach up to 30 cm in length 

and 20 cm in width. Deep red in colour consisting 

usually of wedge shaped fronds that may be split or 

worn in older plants. This species is unbranched 

but several fronds may arise from the base through 

tapering of the frond which may resemble a short 

stipe. Found mainly in the lower littoral and 

sublittoral fringe attached to solid substrate via a 

disc like holdfast 

Dumontia contorta 

Plants tubular and completely hollow throughout 

sometimes appearing a little gelatinous and 

membranous. Branching is irregular and may be 

quite minimal with branches mainly extending from 

main axis. The point of branching may be slightly 

constricted but generally width of filaments ranges 

from 1 to 10 mm broad and can grow up to 50 cm 

long. The tips of the plant often turn green when 

rotting but the plant tends to be dark red or brown in 

colour. Found throughout the littoral often in shallow 

rockpools on both rocky and sandy substrates. 

Common throughout the UK and Ireland. Not to be 

confused with Nemalion helminthoides which is also 

gelatinous but completely solid. 

Dilsea in natural habitat and showing 

split lobe and basal attachment 

Various microscopic views of Dumontia 

showing the different cellular structures 

Dumontia in natural habitat and showing 

branching pattern

Erythrotrichia carnea 

This is a small, filamentous and unbranched species which is 

found growing epiphytically on a range of red, green and brown 

species. The filament can be several cells long and extends from 

a small multicellular disc. It is often very pink in colour and may 

be distinguished from other microscopic filamentous species by 

its stellate (star shaped) chloroplast. Not to be confused with 

Audouinella sp. which are often shorter in length, branched and 

may have hairs or with Bangia atropurpurea. 

Furcellaria lumbricalis 

Plants completely cylindrical, cartilaginous and quite tough and dark red/brown in colour but tips may 

turn green in older plants. Branching is regularly dichotomous and tends to be most dominant at the 

apices which tend to taper appearing fork-like. This species can grow up to 30 cm long and 1-2 mm 

thick. It is often confused with Polyides but may be distinguished by its claw-like basal attachment. It is 

most frequently located in sandy bottomed pools in the lower littoral. 

Furcellaria with claw-like holdfast, with dichotomous branching 

and forked apices and in natural habitat, 

Uniseriate unbranched 

filament of Erythrotrichia 

General form of Furcellaria

Gastroclonium ovatum 

Plant filiform and completely cylindrical throughout also 

quite cartilaginous and fleshy. The most characteristic 

feature is the presence of small bulbous sacs which are 

bunched together at the frond tips. Branching is irregular 

and generally restricted to the upper portions of the 

plant with limited branching at the base although many 

fronds may arise directly from the base. It grows up to 

25cm long and is generally brownish red in colour 

although it often bleaches to brownish yellow. It is 

located on rock surfaces in the lower littoral and 

sublittoral fringe. 

Plant showing sparsely 

branched frond with 

numerous sacs on the 

upper portions of the frond

Gelidium sp. Gracilaria gracilis 

Species quite variable in size and shape but plants 

are generally flesh and cartilaginous. G. pusillum 

tends to have narrow fronds which are cylindrical 

but may be compressed in parts, it is dark 

red/black and wiry with variable branching but 

often arranged in two opposite rows. G. latifolium 

and G. sesquipedale are slightly broader and more 

foliose with regularly flattened fronds and redder in 

colour. All species tend to creep over the rock 

surface, in crevices and overhangs forming mats, 

and are located in the mid to lower littoral. Not to 

be confused with Catenella caespitosa. 

G. latifolium 

showing broader 

compressed frond 

Gelidium pusillum in 

natural habitat and 

under magnification 

Plants filiform, cartilaginous and slightly 

elastic growing up to 60cm long and 1-3mm 

wide. Branching is generally irregular but 

secund at times and may be quite dense in 

some plants often giving a straggly 

appearance. It is usually dark brown in colour 

although may turn green on bleaching. This 

species is quite tolerant of sand and can be 

located in the lower littoral and sublittoral 

fringe and within rockpools attached via a 

discoid holdfast. 

General form of Gracilaria


Plant consisting of uniseriate filaments of cylindrical cells often slightly swollen at each end with apices 

narrow and pointed. Plant tends to be slightly rigid with the texture of coarse hair, with worn plants 

appearing tatty. It is bright red/pink in colour and grows up to 20cm long. It is highly and dichotomously 

branched with reproductive bodies extending from special branches; these are also often surrounded 

by small incurved branchlets or ramuli. Rhizoidal branches may be present in muddy substrates. Found 

mainly in the mid to lower littoral within rockpools and in the sublittoral fringe. 

Long hair-like filaments of H. flosculosus with 

incurved branchlets surrounding reproductive bodies 

Halurus equisetifolius 

Plant filamentous consisting of main 

axis numerously covered with closely 

packed and densely whorled 

uniseriate branches, which are short 

and incurved giving a bottle brush 

appearance. Main axis branching is 

limited and irregular. Generally quite 

coarse in nature and dark red in colour 

growing up to 20cm long. It is located 

in the lower littoral and sublittoral 

fringe on rock surfaces. 

Spongy appearance through 

covering of small Whorled branches 

may resemble a bottle brush.


Plant filamentous and quite bushy with a polysiphonous 

cylindrical main axis and monosiphonous and short 

branching. Fronds generally wide spreading giving a 

slightly delicate feather-like appearance accentuated by 

the short and numerous tufted branchlets which may be 

simple or forked. It is bright pink in colour, pinnate and 

flattened, growing up to 20cm long. It is found in 

rockpools within the lower littoral and sublittoral fringe 

and often on growing on other algae in particular the 

stipes of kelp. 


This is a prostrate species growing 

as a crusts on rock surfaces 

appearing as a dark red stain. Plants 

may be quite extensive covering a 

vast area of rock and is found 

throughout the littoral region. 

Reproductive bodies may be visible 

within pits under magnification. Very 

common and easily distinguished 

from other encrusting algae. 

Flattened feather-like appearance 

of Heterosiphonia showing 

numerous small tufted branchlets 

Hildenbrandia as a 

dark red stain on rock 

surfaces very different 

from other, 

calcareous encrusters

Hypoglossum hypoglossoides 

This species is foliose, very delicate, and membranous, light pink in colour and growing up to 20cm 

long and 4mm wide. Its may characteristic features are the presence of a distinct midrib from which 

bladelets arise. The fronds are pale pink and narrow with pointed tips and may be variously 

branched. It is commonly found in the lower littoral often under overhangs and in the sublittoral fringe. 

Not to be confused with similar branched foliose species with midribs such as Membranoptera sp. 

and Apoglossum sp. 

Delicate and membranous nature of Hypoglossum 

showing branches extending from central midrib 

only and with slender and pointed apices 


The main characteristic of this species is its clearly beaded 

appearance. It is very fleshy, soft and bright pink/red in 

colour and has prominent constrictions at regular intervals 

along the frond creating elongated oval segments. Branching 

can be quite dense, it is often dichotomous and may be both 

whorled or opposite generally extending at right angles from 

the main axis. It is found throughout the littoral particularly in 

overhangs and within mats or turfs. Also commonly located 

on the sides of rockpools. Generally very common. 

Lomentaria in its 

natural habitat 

and showing its 

distinct beaded 

appearance


This plant is very fleshy, soft and rose 

pink in colour and growing up to 15-30cm 

long depending on local conditions. 

Branching pattern is generally irregular, 

numerous with branches constricted at 

the base. General form may vary 

according to level of exposure; in 

exposed conditions branching tends to be 

pinnate appearing flattened, but in 

sheltered areas branching is much more 

variable and luxuriant. It is found 

throughout in lower littoral pools down to 

the sublittoral and may also grow on 

sandy or muddy substrates. 

Natural form of 


showing variable 

colour, presence 

of cystocarps and 

channelled frond 

Reproductive body 

of L. clavellosa 

showing 

constrictions at 

base of branches 

and its general form 


Plant cartilaginous and tough, deep red in colour 

although often turning greeny brown on bleaching 

and growing up to 17cm in length. The frond is 

sometimes quite broad but narrows at the base and 

is in-rolled causing a channel-like appearance, 

though channelling may be slight. The frond may 

also be covered in reproductive bodies (cystocarps) 

present as small knobbles. Plants may be quite 

variable in morphology with some appearing 

twisted and with regularly dichotomous branching. 

It can be found throughout the littoral although is 

most common on the lower shore. Not to be 

confused with Chondrus crispus, which is very 

similar in morphology but is completely flattened.


Plant filamentous and quite bushy with a polysiphonous 

cylindrical main axis and monosiphonous and short 

branching. Fronds generally wide spreading giving a 

slightly delicate feather-like appearance accentuated by 

the short and numerous tufted branchlets which may be 

simple or forked. It is bright pink in colour, pinnate and 

flattened, growing up to 20cm long. It is found in 

rockpools within the lower littoral and sublittoral fringe 

and often on growing on other algae in particular the 

stipes of kelp. 


This is a prostrate species growing 

as a crusts on rock surfaces 

appearing as a dark red stain. Plants 

may be quite extensive covering a 

vast area of rock and is found 

throughout the littoral region. 

Reproductive bodies may be visible 

within pits under magnification. Very 

common and easily distinguished 

from other encrusting algae. 

Flattened feather-like appearance 

of Heterosiphonia showing 

numerous small tufted branchlets 

Hildenbrandia as a 

dark red stain on rock 

surfaces very different 

from other, 

calcareous encrusters

Hypoglossum hypoglossoides 

This species is foliose, very delicate, and membranous, light pink in colour and growing up to 20cm 

long and 4mm wide. Its may characteristic features are the presence of a distinct midrib from which 

bladelets arise. The fronds are pale pink and narrow with pointed tips and may be variously 

branched. It is commonly found in the lower littoral often under overhangs and in the sublittoral fringe. 

Not to be confused with similar branched foliose species with midribs such as Membranoptera sp. 

and Apoglossum sp. 

Delicate and membranous nature of Hypoglossum 

showing branches extending from central midrib 

only and with slender and pointed apices 


The main characteristic of this species is its clearly beaded 

appearance. It is very fleshy, soft and bright pink/red in 

colour and has prominent constrictions at regular intervals 

along the frond creating elongated oval segments. Branching 

can be quite dense, it is often dichotomous and may be both 

whorled or opposite generally extending at right angles from 

the main axis. It is found throughout the littoral particularly in 

overhangs and within mats or turfs. Also commonly located 

on the sides of rockpools. Generally very common. 

Lomentaria in its 

natural habitat 

and showing its 

distinct beaded 

appearance


This plant is very fleshy, soft and rose 

pink in colour and growing up to 15-30cm 

long depending on local conditions. 

Branching pattern is generally irregular, 

numerous with branches constricted at 

the base. General form may vary 

according to level of exposure; in 

exposed conditions branching tends to be 

pinnate appearing flattened, but in 

sheltered areas branching is much more 

variable and luxuriant. It is found 

throughout in lower littoral pools down to 

the sublittoral and may also grow on 

sandy or muddy substrates. 

Natural form of 


showing variable 

colour, presence 

of cystocarps and 

channelled frond 

Reproductive body 

of L. clavellosa 

showing 

constrictions at 

base of branches 

and its general form 


Plant cartilaginous and tough, deep red in colour 

although often turning greeny brown on bleaching 

and growing up to 17cm in length. The frond is 

sometimes quite broad but narrows at the base and 

is in-rolled causing a channel-like appearance, 

though channelling may be slight. The frond may 

also be covered in reproductive bodies (cystocarps) 

present as small knobbles. Plants may be quite 

variable in morphology with some appearing 

twisted and with regularly dichotomous branching. 

It can be found throughout the littoral although is 

most common on the lower shore. Not to be 

confused with Chondrus crispus, which is very 

similar in morphology but is completely flattened.

Melobesia membrancea 

This is a small microscopic, calcareous and epiphytic species. It is 

an encrusting species but considerably different from the general 

calcareous encrusters. This plant requires a high level of 

magnification to be identified. It is characterised by its disc-like 

appearance of radiating cells and is found throughout the littoral 

commonly on hydroids and other algae. Radiating cells of Melobesia 

Membranoptera alata 

Plant foliose, thin, membranous and quite delicate it is 

characterised by its leafy appearance and distinct 

midrib, small side veins are also present but less 

obvious. Branching occurs from the frond margin or 

directly from the main stipe and it is usually highly 

branched either alternately or subdichotomously. 

Plants grow up to 20cm long and frond widths are up to 

5mm, older plants may appear tatty where fronds have 

been worn away. It is found in overhangs and crevices 

and on the sides of rockpools generally in the mid to 

sublittoral areas and is very common. 

Membranoptera with distinct midrib and delicate frond 

and with less prominent side veins


Plant very slippery, gelatinous, squashy and 

completely solid throughout growing up to 25cm long 

and 5mm wide; it may also be quite elastic. 

Branching is limited and irregular, with most 

branching occurring towards the base of the plant. Is 

it frequently reddish brown in colour and is found 

attached to limpets and barnacles in the mid and 

lower littoral. It has a southern distribution. It may be 

confused with Dumontia or Helminthocladia but this 

latter species is generally more clothes in branchlets 

Nemalion with few 

branches and 

growing on barnacles 

Odonthalia dentata 

This species is quite tough despite the broad, 

flat and slightly foliose nature of the frond 

growing up to 30cm long and 15mm wide. It is 

characteristically alternately branched with 

sharply pointed apices giving a tooth edge 

appearance. The thickening of the central frond 

area gives rise to an interrupted midrib. It is 

deep red in colour and can be located in the 

lower to sublittoral fringe particularly around the 

base of kelps. 

General nature of Odonthalia

Osmundea hybrida and Osmundea pinnatifida 

Both these species are very cartilaginous and fleshy 

and dark red-brown in colour but can appear yellowish 

when bleached. Branching pattern varies according to 

species. O. hybrida has branching from all round the 

main axis which tends to be alternate or opposite. It is 

generally cylindrical but may be slightly compressed in 

parts and can grow up to 15cm long with a discoid 

basal attachment. In contrast O. pinnatifida tends to 

be more compressed with branches in a single plane 

only with slightly wider fronds. Microscopic 

examination will reveal a groove in the frond tip and a 

stoloniforous holdfast. O. Hybrida has a terminal pit 

rather than a groove. Both species are located in the 

mid through to sublittoral region and tends to be found 

in amongst turfs in crevices or overhangs and on the 

sides of rockpools, often found together. 

Cylindrical arrangement of branches and 

discoid holdfast on O. hybrida 

Compressed form of O. pinnatifida, with 

single plane branching, also showing its 

wide frond morphological form in its 

natural habitat

Palmaria palmata 

Plant foliose, fleshy and thin but slightly tough 

and elastic. Fronds are quite broad and long 

often wedge shaped and small blades arise from 

the frond margins. It is very variable in shape 

and size, some with very broad and undivided 

fronds and others with long thin and much 

branched fronds, but branching is generally 

variable and irregular. Plant is dark red in colour 

and can grow up to 30cm long. It is commonly 

found in the lower littoral and sublittoral fringe 

within pools and on open rock surface also 

frequently found attached to kelp stipes. 

Phycodrys rubens 

Plant with midrib and side veins very distinct 

throughout. General morphology is thin, 

membranous, delicate and foliose resembling 

an elongated oak leaf with notched frond 

edges and may be up to 9cm wide and 20cm 

long. Branching variable and generally from 

main stipe. Found in the lower littoral and 

sublittoral and often attached to kelp stipes. 

Not to be confused with Delesseria. 

Palmaria showing highly branched form 

Phycodrys with distinct midrib and veins 

and branching from main stipe

Phyllophora sp. 

Plant tough, cartilaginous and foliose, it is 

variable in size depending on the species often 

with a prominent, narrow, cylindrical and long 

stipe. Plants may be broad and fan shaped or 

with long narrow fronds. Branches and division 

variable often with simple blades extending from 

frond margin with narrowing at branch base with 

an interrupted and indistinct midrib. Found in the 

lower to sublittoral fringe on a range of substrate 

types and often attached to kelp stipes. 

Plocamium cartilagineum 

Plant is rose pink in colour, 

filamentous, highly branched and 

slightly delicate. Its main 

characteristic feature is the distinct 

comb-like (secund) branching that 

occurs throughout the plant. The 

fronds tend to be flattened but may 

appear very bushy due to 

numerous branching; growing up 

to 3mm wide and 15cm long. It is 

found in the lower littoral and 

sublittoral often around kelp stipes. 

P. Traillii with short 

terete stipe and 

with numerous 

branchlets 

extending from 

frond margins 

Plocamium with comb-like branching and showing natural 

highly branched and bushy morphology


This species is dark purple and filamentous with a 

soft, fine, and very delicate morphology consisting 

of numerous branches and growing up to 10cm 

long. The plant is generally monosiphonous but 

lower portions may be covered in small cells. 

Branches are both long and short although these 

are not regularly alternate and may appear tatty in 

older plants. They are commonly found in 

amongst mats on both vertical rock and within 

overhangs in the mid but mostly lower littoral. Not 

to be confused with Ptilota gunneri. 

Polyides rotundus 

Plants are cartilaginous and tough, completely terete 

throughout and usually dark red or black in colour. Its 

branching is generally quite regular and dichotomous and 

tends to be more highly branched towards the apices 

which taper to a point. This species is very tolerant of sand 

and is most commonly found in sandy rockpools attaching 

with a discoid holdfast. Easily confused with Furcellaria 

and requires basal portion for correct identification. 

Polyides showing terminal dichotomous 

branching and discoid holdfast 

Plumaria with long and 

short branches, in its 

natural habitat and showing 

monosiphonous fronds

Polysiphonia fucoides 

Plants are generally dark red to black in 

colour growing up to 30cm long and quite 

coarse in texture. Branching is irregular 

and tends to be concentrated towards the 

upper portions of the plant often appearing 

scraggy. It is a polysiphonous species 

consisting of 12-20 siphons with a small 

covering of cells occasionally in the lower 

fronds. It is very common throughout the 

littoral found in numerous habitats. 

Polysiphonia lanosa 

P. Lanosa is dark purple to black, 

filamentous, it can grow up to 8cm long 

and is often quite coarse . It is a 

polysiphonous species consisting of 12- 

24 siphons around a prominent central 

siphon or cell, with distinct dichotomous 

branching often appearing quite tufted. 

It only grows epiphytically on 

Ascophyllum on the upper and mid 

littoral and this is used to distinguish it 

from other species of Polysiphonia. 

P. fucoides in natural 

habitat, its general 

morphology and 

showing the 12 

secondary siphons 

P. lanosa with dichotomous branching, 

growing on Ascophyllum, and showing 

numerous siphons with distinct central 

siphon

Polysiphonia spp. 

These plants are filamentous and 

polysiphonous but will vary 

considerable between species. The 

colour may be light pink to deep red 

and purple or black. The number of 

primary siphons range from 4 to 24 

and depending on the species 

secondary siphons may also be 

present. These characteristics are 

used to distinguish between species. 


Secondary siphons 

Some Polysiphonia species 

may only have 4 to 6 

primary siphons others 

may have secondary 

siphons present, often the 

central siphon cannot be 

easily seen 

Reproductive bodies may be present as cystocarps or tetraspores 

Tetraspores 

They may be found in a number 

of habitats throughout the littoral 

including rockpools, overhangs 

and crevices and may also be 

located in amongst turf formers. 

Shape, size and location of the 

reproductive bodies are also 

quite variable.

Porphyra species 

These plants are foliose and very membranous, thin and polythene-like, tending to be quite elastic. 

They are mostly brownish red in colour with various morphological forms but they all tend to be 

unbranched although some fronds may be highly torn. Species may be differentiated by the location 

of their basal attachment and preferred habitat including position on the shore and host species. P. 

umbilicalis is characterised mainly by its central holdfast from, forming a rosette like frond and is 

located throughout the littoral mainly on open rock surfaces. P. leucosticta is a much smaller plant, 

often quite delicate, pink-red in colour and is found growing epiphytically on other algae particularly 

on the fronds of Fucus sp. attached by a basal holdfast. Also found growing throughout the littoral. 

P. umbilicalis with 

rosette appearance and 

central holdfast 

P. umbilicalis in its 

natural habitat growing 

on open rock surfaces 

P. leucosticta cellular arrangement 

and found growing on Fucus sp.


Plants usually dark red or purple in colour, generally 

very delicate and fine, almost feather-like but quite rigid 

and growing up to 30cm long. Branching generally 

irregular but with distinct alternate arrangement of long 

and short apical branches, branching also tends to be in 

one plane. Often growing in amongst turfs in crevices, 

overhangs and vertical rock in the mid and lower littoral 

and often found on kelp stipes. Not to be confused with 

Plumaria plumosa which is morphologically similar but 

without the regular long-short branching arrangement. 

Rhodomela confervoides 

This species may be quite variable in form depending on 

habitat and season and size may range from 20-60cm long. 

Plant is fine and filiform but often quite cartilaginous with 

irregular branching extending from a more distinct main 

axis, often appearing quite tatty. Branching may be short, 

tufted and spine-like and often densely branched. It is 

reddish brown in colour and is found in shallow rockpools in 

the mid to lower littoral attaching by a discoid holdfast. May 

be found in sandy habitats due to its tolerance. Not to be 

confused with Cystoclonium purpureum which although 

morphologically similar has a claw-like basal attachment or 

with Rhodomela lycopodiodes. 

Ptilota with regular 

and stiff branching 

pattern 

Dense, short 

branching on 

Rhodomela and 

showing discoid 

attachment


This plant consists of uniseriate and microscopic, 

fine filaments made up of long slender cells. It is 

pink in colour and its branching tends to be quite 

limited but generally alternate or dichotomous. 

The main characteristic of this plant is its sand 

tolerance, it is a sand binding species and can 

produce vast carpets over sandy hard substrates. 

It is a mat forming species growing up to 2cm 

long and can be found in the mid to lower littoral 

and may also be located in non sandy 

environments such as overhangs, vertical rock 

and crevices in with other turf forming algae. It is 

similar to species of Audouinella and may be 

distinguished from A. purpurea by the presence of 

pyrenoids and lack of reticulate chloroplast 

resulting in a more sparse colouring of the cell. 

Long narrow 

filaments with 

limited branching 

Forming a turf and trapping sand and 

silt on open rock surfaces 

Showing distinct pyrenoids and 

sparse pink colouring of cells

s A Field Guide to the British Seaweeds - NMBAQC

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