THE STUDY OF THE GEOGRAPHICAL DISTRIBUTION OF THE BETULA IN CHINA

Based on the study of the evolutionary tendency and the geographical distribution of Chinese birch, we obtained some results as follows-1. The Betula is a north temperate genus in distribution, there are 31 native species in China. Among them, 2 species belong to Tropical Asian distribution pattern, 2 Old World Temperate, 7 Temperate Asian, 5 East Asian (1 Sino-Himalayan, 4 Sino-Japanese), and 13 endemic to China. It is obvious that the endemic component is dominant in Chinese birch flora.2. There are 15 species in the adjacent area of the Qinghai-Xizang plateau and the subtropical evergreen broad-leaves forest zone, 10 endemic to this area; 10 in northeast China, the cool-temperate needle-leaves forest zone, the temperate mixed needle-and deciduous broad-leaves forest zone, and the east area of the temperate grassland zone, 5 endemic species; 6 in the Aitai Mountain and the Tianshan Mountain in Xinjiang, all endemic to the area. Therefore, the 3 areas are the 3 centres of the differentiation of the Betula in China.3. There are the most primitive Sect. Betulaster (Spach) Regel and 3 subsections of Sect. Betula in Southwest China. They reflected the main stages of the systematic evolution of the Betula. We consider that the Betula originated in the mountain area of Southwest China, and then dispersed along mountain ranges and rivers.