Abstract:

Northwestern Yunnan is one of biodiversity hotspots in the world.It is believed as important ecological shelter for the Yangtze River water shed.In this paper，species diversity and flora composition of seed plants in the region were investigated coupled with latest literature records and field work in past 5 years.The results showed that in the country scale，Northwestern Yunnan constituted 74% of families，41% of genus，and 20% of species of the total in China.In province scale，Northwestern Yunnan constituted 77% of families，55% of genus，and 43% of plant species of the total in Yunnan.In the composition of tropical elements，the biggest proportions were held by Pantropical elements(16.5%) and Tropical Asian elements(12.2%).In the temperate composition，the biggest proportions were composed by East Asia elements(19.3%) and North Temperate elements(14.5%).The proportion of tropical elements (47%) was close to that of temperate elements (53%)，indicating strong floristic transition.There was obvious temperate character in flora.Strong flora specification was found in the level of families (6.3) and genus (5.1).The richness of plant species was consistent with habitats variation，flora transition and flora specification in this region.There is great significance to testify and develop theories of biodiversity in this region.Therefore，the biodiversity in the region reserved not only the attention in biodiversity protection，but also exploration in theory.Compared with Mt.Yao Nature Reserve，the study area held much more flora elements originated from Tropical Asia which was due to the drift and convolution of ShanMalay Plate.There were strong relationship between Tongbiguan Nature Reserve and this study area in flora zone and the origin，which in some extent testified the existence of Tanaka Line.The joint which linked the study area and Tongbiguan Nature Reserve migt be the Dulongjiang Region.

Key words: Northwestern Yunnan/ flora composition/ specie diversity/ habitats/ flora differentiation/ flora transition