ANALYSIS ON THE FORMATION OF PLANT SPECIES DIVERSITY IN THE YULONG MOUNTAINS,UPPER REACHES OF YANGTZE RIVER

The Yulong Mountains located in Lijiang,northwest of Yunnan,is the highest peak in Yun-ling Mountains range of Hengduan Mountains system.It is encircled by Jinsha River(the upper reaches of Yangtze River) from east,west and north.As one of the three plant diversity centers of plant species in China and according to preliminary statistics,there are about 196 species of algae(belonging to 72 genera and 31 families),20 species of lichens(belonging to 17 families),45 species of liverwort and 130 species of moss,220 species of fern,2 646 species of seed plant(representing 804 genera and 171 families).Among these seed plant,1 631 species are endemic in China,there is about 61.64% of the total seed plants in this small area.The formation of plant species diversity in this region is discussed in this paper.Through paleobotanical data and paleogeologic analysis,it is considered that the richness of plant species diversity in this region is originated from three Tertiary flora——Arctic-tertiary flora,Tethyan Tertiary flora and Boreotropical flora.with the elements of Arctic-Tertiary flora having a most important place.Then under the repeating effects of Neotectonic movement and Quaternary glaciations,for the various climate and environment,these flora further developing,differentiation and evolution in this region,and exchanged with neighboring regional flora,formed the richness of plant species diversity in this area.