J Syst Evol ›› 1997, Vol. 35 ›› Issue (2): 136-147.

• Research Articles • Previous Articles     Next Articles

The Geographic Distribution of the Genus Caragana in Qinghai-Xizang Plateau and Himalayas

Zhang Ming‐li   

  • Published:1997-03-10

Abstract: The Qinghai-Xizang(Tibet) Plateau and the Himalayas, a well-known natural region, is a diversity center and the southern distribution limit of the genus Caragana Fabr.,which is of typical temperate asian areal type. There are twenty-four species and one variety of Caragana recognized by the author in this region, accounting for one-third of total species of the genus. According to the phylogenetic scheme of the genus(Moore, 1968), taxa occurring in this region are all advanced. They consist of not only the rachis-persistent group but also palmate-foliate group. This fact indicates that the differentiation of Caragana is active in this region. The endemism is common, in Caragana most of species are endemic. The vicarism is mainly influenced by some ecological factors such as climate and vegetation . Ser. Bracteolatae Kom. , including five species, forms a vicarism example along the HengduanMountains and Himalayas. The strong adaptation ability of species makes them become some dominant or prominant groups within their shrub communities. The cold and arid adaptations are illustrated by a series of species appearing in forest, grassland and desert as well as the related morphological variation. The areal relationships within the Qinghai-Xizang Plateau and Himalayas were analyzed by using MST (Minimum Spanning Tree) and PAE (Parsimony Analysis of Endemism). The floristic regionalizations of Wu(1979) for China and Mani(1978) for the Himalayas were consulted. The results indicate that the Hengduan Mountains especially its northern part, is a geographic node, from there the species of Caragana adaptively radiate northwards to Tangut and eastwards to southeastern Xizang. The Hengduan Mountain has little relation to the western Himalayas. There is no widespread species of Caragana across many different vegetation zones. The dispersion in Caragana is short in distance and the isolation results from different ecological factors. Although the Qinghai-Xizang Plateau and Himalayas is probably not the place of origin of the genus, the adaptive radiation trend in China might be from Northeast to Southwest according to the relationships between this region and the adjancant regions. In addition, based on the restricted distribution pattern of the genus, together with the fossil records of other genera of the subfamily Papilionoideae, it could be considered that Caragana originated at eastern Siberia in the Late Miocene to Pliocene of the Tertiary.

Key words: Caragana, Qinghai-Xizang Plateau and Himalayas, Distribution pattern, Ecological adaptation, Areal relationship, Origin