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 wereclosely related to the Sino-Himalayan elements, and were historically also somewhat related to the Mediterranean, westernAsian and central Asian elements.%报道了我国西藏拉萨河流域野生种子植物区系的统计分析结果.拉萨河流域内共发现有野生种子植物72科、285属、793种(含变种),分别占西藏野生种子植物的43.90％,24.89％,14.97％,其中裸子植物3科、3属、6种,被子植物69科、282属、787种.被子植物中双子叶植物56科、218属、642种,分别占本区种子植物科、属、种总数的77.78％,76.49％,80.96％,最为丰富;其次是单子叶植物13科、64属、145种,分别占18.06％,22.46％,18.28％.拉萨河流域野生种子植物区系具有4个显著特征:1)种类组成较为丰富,属内种系相对贫乏,种属比2.78,分化程度较弱,单种属和寡种属极为丰富.2)种子植物的区系成分复杂,划分为5个科分布区类型和3个科分布亚型;15个属分布区类型及10个属分布亚型,其中温带科18个,占总科数的56.25％,温带属194个,占总属数的82.20％,温带种705个,占总种数的90.38％,说明本区系具有明显的温带性质.热带成分仅在科级分布型中表现出较大的比例,属、种级热带成分很少,表明本区系在发生发展过程中曾经历过与热带相联系的历史渊源.3)表现出一定程度的特有性,没有中国特有科,中国特有分布属7个,中国特有分布种324个,证实本区系植物的年青性及其较强的演化、特化性质.4)拉萨河流域植物区系与中国-喜马拉雅植物区系的联系紧密,同时与地中海区、西亚至中亚植物区系亦有深远的渊源.
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