Dark to dull green unbranched uniseriate filaments typically found in localized carpets (among other greens) on rock and other hard substrata (Featured Image above). Filaments range from 1-8 cm long and are relatively stiff and straight (a look easily betrayed by a hasty field press; Image A). At the base the lowest 2-12 cells (typically between 100-900 µm from the substratum) can produce descending intramatrical (i.e. produced within the “matrix” or cell walls and surrounding cuticle) rhizoids (Image B), which are cut off from the lower margins of the cells (Image C). Observations are too few to rule out the co-development of extramatrical rhizoids. Cells here are typically square to rectangular, 42-58 µm wide by 50-97 µm tall. Mid thallus the cells are 55-70 µm wide by 38-54 µm tall, being squat with rounded outlines (slight barrel shape) and in fresh material numerous pyrenoids are evident in the parietal chloroplast of each cell (Image D). Towards the tops of filaments the vegetative cells become their widest, 59-79 µm, and occur in regions of regular squat to disc-shaped cells, 25-50 µm tall (Image E) or regions of cells that are highly variable in length, 40-208 µm (Image F). Reproductive structures, putative gametangia, are squat in outline and barrel-shaped, 85-90 µm wide by 60-76 µm tall (Image G). We have not encountered the zygote, “Codiolum gregarium” stage, of this species in our biodiversity surveys of the Canadian flora to date, which may be a sampling artifact or owing to an asexual life history for the area from which our collections were made.
Our genetically verified collections are few (n = 4) for this species and confined to the NW Atlantic. The reported presence of this genetic group in both the Arctic and BC awaits molecular confirmation. The morphological data provided here result from a single pressed voucher (GWS006133) and a recent collection (GWS044494) awaiting molecular confirmation. An added complication is that a moniliform collection from QC, which was morphologically identified as Urospora wormskioldii (Mertens ex Hornemann) Rosenvinge, yielded rbcL data for Urospora penicilliformis. There were a few filaments tentatively consistent with the latter tangled with the voucher of the former, and as such this anomaly may be simply a PCR issue. Clearly more genetically verified collections are necessary to understand the full ecological and biogeographical range of this species and in fact all species of the genus Urospora.
Our few collections are from late winter to early spring, growing on rock in the upper to lower intertidal, as well as tangled in vegetation near freshwater outflow in an estuary. In preliminary phylogenetic analyses with both rbcL-3P and tufA, Urospora penicilliformis, the type of the genus, joins Ulothrix speciosa (Carmichael) Kützing (= Urospora speciosa (Carmichael) Leblond ex Hamel on this site) to the exclusion of the other species in our flora assigned to Urospora. Taxonomic work is necessary.
It is common for what otherwise looks like a unialgal carpet on rock, or mat of green filaments in an estuary, to be a chaotic mix of green species including, among others, various Blidingia spp., Percursaria percursa (C.Agardh) Rosenvinge, Rhizoclonium spp., Rosenvingiella polyrhiza (Rosenvinge) P.C.Silva, Urospora spp. and Ulothrix spp. Identification should be done carefully, as should attempting to match DNA sequences to individual species. Specimen GWS044494 used here for morphological observations consists of a few filaments dissected from a mat of Ulothrix flacca (Dillwyn)Thuret (Image H). Owing to the wonders of PCR, a clean sequence could be from any one of the species present in a collection and not necessarily the dominant one on which the microscopical identification was based. Consequently, I am not yet 100% certain that the genetic groups and morphospecies completely align for this page. Neither am I convinced that the correct binomial is applied to the morphospecies as outlined here. This is my best guess after consulting the pertinent literature (mostly Scagel (1966), Burrows (1991), Sears (2002), Brodie et al. (2007), Mathieson & Dawes (2017) and Gabrielson & Lindstrom (2018)). Considerable work remains for this genus in our flora.
Image A. Filaments on the periphery of these green clumps reveal the stiff and relatively straight habit of this species (upper intertidal on rock, Escoumins (old ferry terminal), QC; GWS006133).
Image B. Vegetative cells near the filament base with well developed intramatrical rhizoids arising from the lower cells (GWS006133; rehydrated from press).
Image C. Close up of the intramatrical rhizoids (GWS006133; rehydrated from press).
Image D. Cells mid thallus are squat to disc-like with rounded outlines; each cell has a parietal chloroplast in which numerous pyrenoids are evident (GWS044494).
Image E. Vegetative cells closer to the top of a filament consistently disc shaped (GWS006133; rehydrated from press).
Image F. Vegetative cells near the top of a filament highly variable in length (GWS044494).
Image G. Putative gametangia in the upper portions of a filament (GWS044494).
Image H. A skein of Ulothrix flacca (Dillwyn)Thuret from which a few filaments of Urospora penicilliformis were recovered (GWS044494).
Seaweed of Canada 