The Himalayan chain consists of the complex system of nearly parallel ranges of Tertiary mountains, stretching over nearly 3000 km, almost from the borders of Afghanistan in the west to the north of Burma in the east, approximately between 72° and 91°E and 27° and 36°N. The Himalayas are usually divided into four geographical divisions; 1) the Assam Himalaya, 2) Nepal Himalaya, 3) Kumaon-Garhwal Himalaya and 4) Punjab-Kashmir (Northwest) Himalaya. The Nepal Himalaya is about 900 km long from the Kali River eastwards to the Tista River. Its highest peaks such as Api, Dhaulagiri, Annapurna, Makalu, Everest and Kanchenjunga, are perpetually clothed in ice and snow and reach between 6755 m and 8848 m in altitude.

Since Wallich recorded various Himalayan plants from Gossain Than (actually Gosainkund, N of Kathmandu) in 1824, many botanists like Roylc (1833-40), Hooker (1872-97), Hooker and Thomson (1855),Kitamura (1955), Hara (1966, 1971), Hara et al. (1978, 79 & 82), have greatly enriched our knowledge of the alpine flora of the Himalayas (see Dobremez et al., 1972; Mani, 1978; Rajbhandari, 1976; Stearn, 1978). It is noticeable that in the 20th century large numbers of collections of the alpine plants were brought by W. W. Smith; Kingdon-Ward; Ludlow & Sherriff and others; Polunin, Sykes & Williams; Stainton, Sykes & Williams; Nakao; Zimmermann; Hara and his associates; the staff of Department of Medicinal Plants (Kathmandu); and many other collectors and explorers (Taylor, 1975; Sutton, 1978). Without these collections it might be impossible to reveal the floristic features. The flowering plants of the Nepal Himalaya have been especially well surveyed by British and Japanese botanists (Smith, 1913;Marquand, 1929; Hara, 1966, 71; Ohashi, 1975; Hara et al., 1978, 79 & 82). The ecological character of the alpine vegetation has also been studied by many workers (see Dobremez et al., 1972).

In common usage, the alpine zone is a vegetative zone that occurs above the tree line and below the snow line on temperate and tropical mountains. In the Himalayas, generally, the lower part of the alpine zone is a summer grazing-ground with meadows bright with alpine flowers and the upper parts have a high-alpine flora, with species adapted to withstand the extremes of cold and desiccation (Polunin & Stainton, 1984). Mani (1978) considered the alpine zone (comprising meadows, xerophile and discontinuous vegetation) to be above 3900 m on southern slopes and 4100 m on northern slopes. Hara et al, (1978) generalized that alpine scrub is found between 3700 m and 4400 m, dry scrub between 3500 m and 4600 m, and discontinuous cover of dwarf perennial herbs above 4900 m in Nepal. However, it is difficult to delimit the zone by altitude since real variation in alpine flora depends on local environments.

Li (1981) considered that the subnival vegetation of Tibet has obviously different origin and formation processes from those of mountainous regions in northern Europe, Asia, and North America and was little influenced by the arctic flora. He made no mention of the relationship to that of the Himalayas. The subnival vegetation, which is defined by him as vanguard plant communities in the subnival belt between the continual plant cover and the snow line, constitutes a characteristic feature of the high alpine zone. He concluded that the vegetation has mainly evolved from the original local alpine vegetation.

I have compiled a checklist of flowering plants which are known to occur in the alpine zone above 4000 m in altitude of the Nepal Himalaya (see Appendix). It is my hope that the present checklist will be found useful as a basis for the compilation of a modern and comprehensive manual of the Himalayan alpine flora, I also anticipate that it may stimulate more general quantitative and experimental approaches to the evolutionary history and diversification of the alpine flora. When I compiled this checklist, I attached great importance to "An enumeration of the flowering plants of Nepal" (3 vols.) by Hara et al. (1978, 79 & 82). I have arranged families in alphabetical order within the gymnosperms, monocotyledons and dicotyledons, I accept the designation of family in its most traditional sense.

The total number of the species found in the alpine zone of Nepal is 1227, of which six are gymnosperms, 192 monocotyledons and 1029 dicotyledons. The largest family in the alpine zone is Compositae. with 140 species (Colour Plates 1 & 2). Saxifragaceae (86 species, Colour Plate 5; Plates 1 &2), Scrophulariaceae (74), Ranunculaceae (73), Gramineae (70), Gentianaceae (63) and Primulaceae (59) follow. Some species reach to areas near the snow line and are therefore subnival vegetations. The Guinness Book of Records (1984) gives the highest species as Ermania himalayensis (Cambess) O. E. Schuiz and Ranunculus lobatus Jacq. ex Cambess (not known from Nepal), which were found at an altitude of 6400 m on Mt. Kamet (7756 m) in the Himalayas by N. D. Jayal.

In Nepal it is quite remarkable that nearly the half of the total number of the species of the alpine flora belong to only 29 genera (Table 1). It is also noticeable that almost all of the genera listed in Table 1 are common and diversified in both arctic and temperate regions of the northern hemisphere. Some of the species found in the Himalayan alpine zone are also distributed widely in both the arctic and other alpine zones of the northern hemisphere; these are Epilobium latifolium L., Oxyria digyna (L.) Hall, Bistorta vivipara (L.) S. F. Gray, Trisetum spicatum (L.) K. Richtcr, Potamogeton filiformis Pers., P. natans L.

The total number of endemic species in the alpine flora of Nepal is not known. The number of endemic species and the frequency of endemic species of the largest eight genera of the alpine flora are shown in Table 2. Except for Carex, the incidence of endemic species exceeds 50% and generally reaches 70% to 80%. The highest endemism is found in Primula (85.4%).

The high incidence of endemism found in these largest (diversified) genera is quite remarkable and is an indication both of the active evolution in the alpine zone of the Himalayas and also of a considerable degree of isolation. It is considered that many of these endemics are species of apparently recent origin with close relatives in the alpine zone itself, in the lowland vegetation of the Himalayas and also in the region around the central Asiatic highland. In the case of the subnival vegetation of Tibet (Li, 1981), in my opinion, the high endemism of species gave Li the impression that the flora is autochthonous, as indicated by his "local original alpine vegetation."

I give some account of the significance of the central Asiatic highland (Fig. 1). In the case of the genus Rhodiola the species are concentratedly distributed in the region around the central Asiatic highland (Fig. 2). It is quite probable that the Himalayan flora had open intercourse with those of the arctic regions via the east and west margins of the highland, particularly in ages of climatic fluctuation. Thia floriatic connection of the Himalayas through the central Asiatic highland is supported by the distribution pattern and/or the presence of common or corresponding species with the arctic regions (Figs. 3 & 4). Thus, I would like to suggest the name "Central Asiatic Highland Corridor" as an important pass for the migration of the flora between the arctic regions and the Himalayas as well as E Tibet and SW China (particularly, Yunnan & Szechuan). In the alpine flora of the Nepal Himalaya, the east central Asiatic highland corridor is thought to play an important role in interchange of the floristic elements particularly with E Tibet and SW China. In Rhodiola about half of the alpine species of Nepal are also distributed in E Tibet and/or SW China.

One of the striking features of the high alpine zone is the short and fleeting growing season for plants. In our field experience at Phujeng La in east Nepal, at altitudes of 4800 m the duration of the growing season can be estimated at approximately 10 to 11 weeks (70-77 daya) (Ohba, 1982). At altitudes above 4500 m, blooming is thought to concentrate in the period from the middle of July to about the third week of August. At Phujeng La, I observed that Rhodiola coccinea (Royle) A. Boriss. prepared new flowering stems and cauline leaves just before the thawing of snow. It appears to be completely covered by snow throughout winter and the whole of spring (Ohba, 1982).

It is noticeable that the Himalayan alpine flora, particularly the high alpine, contains various curious plants with unusual forms such as "cushion," "snowball" and "hothouse" plants. It is remarkable that these unusual forms are distributed in several genera among different families. In the case of "cushion" plants, the typical form is found in the genera Androsace (Primulaceae), Saxifraga (Saxifragaceae), Rhodiola (Crassulaceae), Thylacospermum and Arenaria (Caryophyllaceae).

The "snowball" plants are represented by Sanssurea gossypiphora D. Don, which looks like a snowball. The whole plant is nearly globular and densely covered with whitish woolly hairs, which are produced from the surface of the upper leaves. More interesting is the fact that a chamber is formed above the inflorescence. The chamber is made of the upper leaves themselves covered by the long woolly hairs, is completely protected from winds and keeps warm in the daytime even if the outside temperature suddenly decreases. This means that the chamber is quite suitable as a resting place for bees or flies which act as the pollinator of this flower, particularly when the weather suddenly becomes unfavourable (strong winds, heavy clouds, etc.).

The chamber, however, seems to have an effect not only on pollination but also on growth. The growth of the apical meristem which is located at the bottom of the chamber may possibly be accelerated by the constant and rather higher temperature (Ohba & Kikuchi, unpublished). When the plant is young, the chamber does not develop but the stem apex is covered with the leaves and their hairs.

Saussnrea graminifolia Wall. ex DC. (Fig. 5) has no chamber, but the stem apex is densely covered with white woolly hairs. Hence, the primary function of the hairs is thought to be thermal insulation of the apical meristem. Such insulation seems to be significant in the high alpine zone with its extremely limited growth season.

Rheum nobile Hook. f. et Thoms. and Saussurea obvallata (DC.) Edgew. (Colour Plate 1) are representative of "hothouse" plants. The inflorescence is sheltered by papery and translucent leafy bracts that can be compared to the glass of a hothouse. Nakao (1964) wrote: "The flowers open in the self-made warm room in which the pollination insects are working actively under favourable conditions inside. The striking device has obviously the selective advantage of pollination capacity." However, even in these cases, the bracts seem to accelerate growth of the plant itself as do the long hairs of the "snowball plant."

Phlomis rotata Benth. ex Hook. f. (Colour Plate 4c) has a rosette of rounded thick leaves pressed flat to the ground. It is remarkable that the individuals growing among rocks or rock crevices have elongate stem and lack the prominent rosette. That is, the stemless individuals with the prominent rosette are only found on flatter, moss covered soil ground (Ohba, 1986). The development of the prominent rosulate leaf is considered to be related to terrestrial heat as in the case of "cushion" plants.

Kevan (1975) discovered that several arctic flowers, mainly bowl-shaped ones like Dryas integrifolia and Papaver radicatum, act as solar reflectors and function to concentrate or focus heat which contributes to floral metabolism and reproductive process, particularly insect pollination. Such solar concentration mechanisms are thought to be present in Himalayan alpine plants because radiant heat focusing is also quite important to reproduction and metabolism in the alpine zones. This is another adaptation related to insolation.

It is generally thought that arctic plants are independent of insects for pollination and seed-sets. However, Kevan (1970) shows that most of the dicotyledons around Hanzen camp (81°49'N, 71°18'W) in Ellesmere Island, Canada, display all the attributes of entomophily. As the result of an experiment of pollination he discovered that the hermaphroditic flowers are most frequently visited by insects and that local differences in seed-set of entomophilous flowers are correlated with the suitability of the region to pollination (Kevan, 1972). In contrast to this, the pollination ecology of the Himalayan alpine plants is incomplete.

In Himalayan Saxifraga, most species of the section Ciliatae (=Hirculus) are pro-tandrous and seem to be still operating self-incompatibility mechanisms. However, one or two among ten stamens are bent inside and their .anthers associate with the stigma. Even if the remaining stamens are elongated and straight, these one or two continue to associate with the stigma. When the anthers of the remaining stamens disperse the pollen and the stigma is receptive, the anthers of the associated stamens become mature (Plate 2).

Such a peculiar stamen-pistil movement and mutual contact in Saxifraga had already been discovered in some arctic species by Warming (1909). This can be regarded as a partial self-fertilization and, in my opinion, a kind of "insurance" to avoid sterility. Like the arctic plants, many of the alpine flowering plants of the Himalayas are independent of insects for reproduction, being autogamous, apomictic or anemophilous.

Cytological data on the Himalayan alpine species are quite insufficient, almost all remaining cytologically unknown. In the present research we have made an effort to investigate the alpine flora using cytological techniques. Cytology is now widely recognized as an important approach to reveal. the evolutionary history and diversification of flora.

Generally, the frequency of polyploids in a flora has a tendency to increase from equitable to more severe areas. The great ecological amplitude which polyploid species can acquire gives them a high degree of buffering against environmental changes taking place over long periods of time, due to glaciation, mountain building and degradation, and overall fluctuations in the earth climate (Stebbina, 1971). Indeed, Hanelt (1966) thought that the polyploids sometimes have a higher frequency in high mountains than in the neighbouring lowlands, but this is not always the case. He gives percentage figures ranging from 45 to 85% polyploids in various high mountain floras of Eurasia, the Americans and New Guinea. Löve and Löve (1967) pointed out that the frequency of polyploidy is significantly higher in the alpine zone in the case of Mt. Washington in the White Mountains (New Hampshire) where 63.6% of the alpine taxa of vascular plants are polyploid. In the case of the arctic flora, the frequency of polyploida is higher than the floras of the lower latitudes (Hanelt, 1966; Löve & Löve, 1975). The recent estimation of frequency of polyploid species in the vascular flora of the arctic region as a whole is almost 60% in the low arctic, but 70% in the high arctic and 80% in high-arctic endemics (Löve & Löve, 1975).

In our observation on the Himalayan Saxifraga, however, diploids prevail and the polyploid share is only 17% (Wakabayashi & Ohba, 1988). Thus, polyploidy is not thought to play an important role in species diversification in the alpine flora of the Nepal Himalaya. However, further observations in the various taxa are needed to reveal the role of polyploidy in the Himalayas.

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