关键词: 拉萨河流域, 野生种子植物, 区系, 西藏

Abstract:

This paper reports the results of a statistical analysis on flora of the seed plants from the Lhasa River reaches, Tibet, China. There were 793 species (and varieties) in 285 genera of 72 families of wild seed plants found in the area, accounting for 43.90% in species, 24.89% in genera, and 14.97% in families of the seed plants from Tibet. Six species in three genera of three families belonged to gymnosperms, and the other 787 species in 282 genera of 69 families belonged to angiosperms. In the angiosperms,the dicots, with 642 species in 218 genera of 56 families, were predominant in the floristic composition and accounted for 77.78% in species, 76.49% in genera, and 80.96% in families of the seed plants from Tibet. The monocots had 145 species in 64 genera of 13 families, and accounted for 18.06%, 22.46%, and 18.28%, respectively. The seed plants in the Lhasa river reaches had four salient characteristics. 1) The species in the area were abundant in number, but the species within a genus were relatively scarce, and thus the number of species within a genus is relatively few, with the ratio of species to genus being 2.78. The genera with only one or a few species were abundant in the flora. 2) The flora was complicated in composition, with the families representing five areal-types and three subtypes, and the genera representing 15 areal-types and 10 subtypes. Among these elements, temperate ones were predominant, including 18 families, 194 genera, and 705 species, accounting for respectively 56.25%, 82.20%, and 90.38% of the total in the area. This result clearly showed a temperate nature of the flora in question. Tropical elements accounted for a relatively high proportion only at the familial level, but a very low proportion at both generic and specific levels, suggesting that this flora might have some historical relationships with tropical floras in the course of its origin and development. 3) The endemism was not high; there were no families endemic to China in the area, although seven genera and 324 species were China specific in the area. This reflected the relative youthfulness and strong differentiation and specialization of the flora in the area. 4) Floristically the seed plants from the Lhasa river reaches were closely related to the Sino-Himalayan elements, and were historically also somewhat related to the Mediterranean, western Asian and central Asian elements.

Key words: Lhasa river reaches, wild seed plants, flora, Tibet