青藏高原的植物区系是泛北极植物区的一部分。这个区系所代表的地域称为青藏高原植物亚区,青海和西藏的主要部分都属于这个亚区。青藏高原植物亚区的西藏部分包括雅鲁藏布江中上游,昆仑山和唐古拉山以南的广大地域^[1]。这个亚区由于历史短暂,环境高寒,植物区系比较贫乏,植被是以草甸灌丛为主的无林地区。

Qinghai-Xizang plateau flora belongs to a floristic subkingdom of Holarctic Kingdom. This subkingdom in Xizang can be divided into 4 regions:(1)Yaluzangbu Valley region:the species of seed plant in this region amount to 1003, making up 19.38% of the total number in Xizang. The sum of endemic species in the region is 159, making up 15.8% of the total number. The flora of Yaluzangbu Valley region mainly originates from East Ximalaya Mountains and Hengduan Mountains. The monotypie genus, Ajaniopsis peniciliformis, is the endemic of the Yaluzangbu Valley. (2)Tangut region:there are 349 species in the region, being 6.74% of the total number in Xizang, of which the endemic species in the region is 10 in number. Two monotyPie genera, both are respectively endemic genera of the Qinghai-Xizang plateau and Hengduan Mountains, are found here, Metaritrichium microuloides and Przewalskia tangutica. In fact, Tangut flora represents an intermediate one between Qinghai-Xizang plateau and Hengduan Mountains. (3)Qiang-Tang region:it is the most poor in flora of Xizang. The spaties of seed plant amount to 255, being only 4.93% of total number in Xizang. The regional endemic species are 18, belonging to 13 genera of 7 families. It is considered that the present flora in Qiang-Tang derived from Himalayan flora and mixed with a great number of Tethysian elements. (4)All region:there are 547 species of seed plant,making up 10.57% of total number in Xizang, containing 41 regional endemic species. The Ali flora seems to be closely related with TethySian one. The Biebersteinia odora and Capparis spinosa oceuring in Ali, may be the few relicts of tropical elements of the Tethys.