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A Taxonomic Revision of Oligotrichum DC. in Lam. & DC. (Polytrichaceae) in the Sino-Himalaya by Isuru Udayanga Kariyawasam Thesis submitted in the partial fulfillment for the MSc in the Biodiversity & Taxonomy of Plants September 2013 CHAPTER 05 DISCUSSION “Discussion itself is what most matters, the fact that we can reason together easily with a blend of wit and seriousness, and always allowing room for alternating views”. —Stephen Greenblatt, The Swerve: How the World Became Modern. 5.1 Ecology 5.1.1 Substrate and Habitat In the Atlas of the Bryophytes of Britain and Ireland, Long (1985) described the habitat of O. hercynicum in Britain and Ireland as: ‘A calcifuge pioneer of disturbed ground in the mountains, as on shingle by streams, gravelly footpaths, eroding slopes, gullies and stony screes, sometimes in late-snow areas; occasionally on lake margins where it may be intermittently inundated”. According to the data recorded on herbarium specimens, these particular habitat preferences also apply to the Sino-Himalayan Oligotrichum species. In addition, important additional habitats in the Sino-Himalaya include glacial moraines and melting snow beds (O. glaciale) at high elevations (3700–4690 m), and frequently on poor soils and gravel of banks of road cuttings (almost all taxa of Sino-Himalayan Oligotrichum). The genus is typically found above the timber line (in the Sino- Himalaya this is often between 3000 and 4000 metres) but also in the temperate forest zones, but always in disturbed open areas in the forest (Figures 18 & 19) as on streamsides and banks of road cuttings. Like almost all Polytrichaceae, Oligotrichum favours nutrient-poor and lime-poor acid substrates, so it is much less common in limestone areas. Oligotrichum falcatum is mentioned as being found in aquatic habitats in arcto-alpine areas in Alaska (Long, 1985) which gives it a beautiful silvery pale colour when submerged (Steere, 1958). But there is no record found from aquatic habitats of O. 91 falcatum from the Sino-Himalaya, but several species are reported from lake margins, glacial melt-water streams and river banks. For O. nepalense habitat is unknown. 5.1.2. Altitude O. glaciale occupies the highest altitude range (ca.3800–4830 m) of any Oligotrichum species in the Sino-Himalaya, followed by O. nepalense (ca. 4600 m) and O. falcatum (3900–4460m). O. semilamellatum and O. falcifolium are found in more or less the same altitudinal range (ca, 1470–3352 and 1720–3550 m respectively), which in turn could reflect some morphological synapomorphies between the two taxa. Grau et al (2007) argued that the reduction in the species richness of the bryoflora in lowlands of Sino-Himalaya, as represented by the studied taxa, is due to the combination of habitat loss, inadequate sampling and unfavourable climatic conditions. The altitudinal range of Oligotrichum exceeds the elevation at which species richness is highest in the Himalaya, 2500m (Grau, et al, 2007). Water availability is a less of an ecophysiological barrier for mosses in high altitudes, and being epilithic on moist soil and rocky substrates, they are not dependent on the altitudinal range of trees as substratum. Bell & Hyvönen (2012) suggested that the reduced gametophytic morphology of Oligotrichum is associated with the prevailing environmental and climatic conditions they exist under. They further stated that the morphology of Oligotrichum is usually associated with open and exposed habitats subject to high precipitation, strong winds, and low nutrient availability. Hence these life forms show adaptations to extreme alpine conditions, where the potential for CO2 uptake is less limiting due to other environmental stresses which add barriers to photosynthetic activity and growth rate. This is evident in the morphologies of O. glaciale and O. nepalense which grow at very high altitudes. Both have dwarf growth forms (0.5–1.0 cm) and grow in tufts. The highly dissected compactly arranged lamellae on the leaf lamina of O. nepalense (Figure 5) and strongly wavy lamellae (Figure 9) of O. glaciale may mean that the strong development of lamellae serves to accelerate the rate of photosynthesis for the growth and survival in extreme high mountain habitats Habitat-associated climatic 92 factors like reduced irradiance levels due to very frequent cloud cover may also affect the growth form of Oligotrichum (Bell & Hyvönen, 2012). The reduced gametophytic morphology associated with the ecology and altitudinal changes under climatic extremes could offer an interesting study to interpret the phytogeography of Oligotrichum in the Sino-Himalaya. Bell & Hyvönen (2012) in their study offer the following explanation: “The association of the reduced gametophytic morphology with isolated, extreme habitats are consistent with it having arisen convergently on multiple occasions and without similarly adapted species being forced into competition with each other for the same niches. In a sense, this association could act as an engine for the generation of cryptic or partially cryptic phylogenetic diversity, which is best explored with the aid of molecular level sequence data.” 93 Figure 18. Photograph of Handel-Mazzetti’s type locality of O. obtusatum in Xiangshuihe, Ma’er Shan, Yunnan, China by D.G.Long, May 2012 Figure 19. Photograph of the habitat of O. crossidioides in Gaoligong Shan, Yunnan, China (locality of Shevock 25567) by D.G. Long, August 2005 94 5.2 Phytogeography 5.2.1 Sino-Himalayan Distribution In the Sino-Himalaya the following regional totals of Oligotrichum are recorded. NW India & Pakistan, 4 species (O. obtusatum new); Nepal, 6 species (O. glaciale, O. falcatum new); NE India, 5 species (O. falcatum and O. obtusatum new); Bhutan, 1 species; Xizang, 2 species; Sichuan, 1 species (O. obtusatum, new); and Yunnan, 5 species (O. glaciale, new). The following table (Table 4) summarises the occurrence of Oligotrichum in the Sino-Himalaya. Table 4. Occurrence of Oligotrichum in the Sino-Himalaya. Species NW Nepal NE Bhutan Xizang Sichuan Yunnan India India O. crossidioides _ _ _ _ + _ + O. aligerum _ _ _ _ _ _ + O. falcatum _ + + _ + _ _ O. nepalense _ + _ _ _ _ _ O. obtusatum + + + _ _ + + O. semilamellatum + + + + _ _ + O. falcifolium + + + _ _ _ _ O. glaciale + + + _ _ _ + Of the eight Oligotrichum species found in the Sino-Himalaya, three show highly localised distributions, with O. nepalense restricted to the Himalaya (only in Nepal), and O. crossidioides and O. aligerum restricted to western China. The remaining five species (O. falcatum, O. falcifolium, O. glaciale, O. obtusatum and O. semilamellatum) occur more widely from the Himalaya to China, though each has its own special distribution pattern. However, the rarity of records from Bhutan and Assam is probably due to lack of collection rather than genuine rarity, so these distributions cannot be interpreted as genuine disjunctions. Furthermore, until the present study, O. glaciale was considered an endemic to NW India, but know it is known to occur from Pakistan to China. The conclusion is therefore that all distributions of Oligotrichum in the Sino-Himalaya must be considered as provisional, 95 and it is likely that further field work will show that some species are more widespread. Hence any biogeographical conclusions are very tentative. 5.2.2 Worldwide Distribution The following table (Table 5) summarises the world-wide distribution of Sino- Himalayan Oligotrichum species Table 5. Worldwide distribution of regional Oligotrichum species. Species North Central South Africa Europe Asia Australia America America America O. crossidioides _ _ _ _ _ + _ O. aligerum _ + _ _ _ + _ O. falcatum + _ _ _ _ + _ O. nepalense _ _ _ _ _ + _ O. obtusatum _ _ _ _ _ + _ O. semilamellatum _ _ _ _ _ + _ O. falcifolium _ _ _ _ _ + _ O. glaciale _ _ _ _ _ + _ In contrast to the very limited conclusions possible within the Sino-Himalaya, the global distribution patterns are clearer. Six of the species are restricted to the Sino- Himalaya (O. crossidioides, O. falcifolium, O. glaciale, O. nepalense, O. obtusatum and O. semilamellatum) and the other two (O. aligerum and O. falcatum) extend beyond the Sino-Himalaya. O. aligerum appears to be a circum-Pacific taxon occurring from Central Amertica through North America, Japan, China, Korea and the Philippines. O. falcatum is an Arctic species found in Arctic America and Greenland, disjunct in the Sino-Himalaya. None of the eight species occurs in the southern hemisphere or Africa. Table 5 therefore suggests strongly that the Sino-Himalayan is the global centre of diversity of the genus Oligotrichum. 96 CONCLUSIONS This study provides the first full taxonomic account of Oligotrichum DC. in Lam. & DC. from the Sino-Himalaya, confirming eight Oligotrichum species from the region. Three new national and regional records of O. glaciale (from Nepal, Pakistan and China: Yunnan) are reported along with two new records of O. falcatum (from India and Nepal) and two new records of O. obtusatum (from India and China: Sichuan). The identity of the puzzling “Oligotrichum-like” specimen collected by Terry Hedderson from Pakistan is resolved by confirming it as O. glaciale C.C.Towns. The sporophytes of O. glaciale were discovered in this study from a collection of D.G. Long (Long, 22696, E) from Sikkim, India. Similarities of the morphologies between O. glaciale and the closely related taxon (based on the molecular phylogenetic study done by Bell & Hyvönen, 2012), the African Oligotrichum cavallii (Negri) G.L.Sm. is addressed. Further molecular study is needed to solve the precise taxonomic status of O. glaciale which may prove to belong to an undescribed genus of the family Polytrichaceae. The taxonomic difficulties presented by Oligotrichum specimens has led to many misidentifications some of the widely distributed species, which are morpholgically rather variable, particularly O.semilamellatum (Hook.f.) Mitt.