Abstract: Qinling Mountain is the natural geographic dividing line between South and North China. Taibai Mountaia about altitute of 3 767 m above sea level is the highest in this region and eastward to Qinghai-Xizang (Tibet) Plateau. There are 41 species in this region, belonging to 14 sections and 3 subgenera. This paper deals with the morphological variation and evolution of the said genus by means of parsimony analysis, the presentation of the floristic feature and geographic differentiation is by means of cluster analysis. The results are as following: 1, The cladogram indicates that the directions of morphological evolution are from multistaminal willows, two'-staminal willows to one-starn inal willows, from, Subgen Salix, Subgen. Vetrix to Subgen. Helix, and from the groups in the southern slope to that of the northern slope of Qinling Mountain. The groups of Qinghai-Xizang Plateau elements have obvious variation in this region. 2. This region is influenced striking by the floristic elements of adj-iacent regions including North China Temperate, Central China Subtropic and Southwest China Subtropic elements. The transition could be seen in some groups. Sect。Wilsonianae with mlultistam'ens endemic to China, is extending from the southern China northwards to the southern slope of this region, such as S. wilsonii, S. rosthomii and S. paraplesia. Sect. Pentandrar, Sect. Vetrix, Sect. Vimen and Sect. Haoanae are dispersing northward from' Qinling Mountain or its northern slope, such as S. chaenomeldoides, S. matsudana, S. sinica, S. characta, S. viminalis and S. sinopurpurea, 3. There are more than 22 species (4 endemic species) of Salix in Teai-bai Mountain, It is the richest region in Qinling Mountains The flo!ristic elements are mainly belonging to North Temperate and Qinghai-Xizang Plateau elements. Species distributed above 3 000m are chief the alpine elements of Qinghai-Xizang Plateau and endemic distributions. Form Salix cupular is is peculiar in the alpine m,eadow zone above 3500m. 4. The phenogram for area of species shows that there are three centers of the species differentiation, namely, Ningsban-Shiquan conunties (42、51 in Fig. 1) representing Central China elements, Wenxian-Wudu counties (48、34) representing Southwest China elements and Taibai Mountain (26) representing North China and Qinghai-Xizang Plateau elements The ancient roads from the southern to the northern slope may be the、pathways of dispersal and migration of the species, the Hanshui River and Jialing River is reponding respectively to the elements of Central China and Qinghai-Xizang Plateau.

Key words: Salix, Qinling Mountain, distribution and differentiation, numerical approaches