青藏高原和喜马拉雅地区锦鸡儿属植物的地理分布

锦鸡儿属Caragana是一个典型的温带亚洲分布属。本属在青藏高原和喜马拉雅约有24种1变种，约占整个属的1／3。这些种类几乎全部处于演化高级阶段，且既有叶轴宿存类群，也有假掌状叶类群。反映出种的分化很活跃，在横断山地区形成本属的分布中心、分化中心。本区内绝大多数种类是特有分布。替代现象主要受气候、植被变化作用，沿横断山和喜马拉雅分布的长齿系Ser. Bracteolatae Kom．是一个典型的替代分布类群。锦鸡儿属植物生态适应性很强，可在其生长的灌丛中形成优势种。 寒化和旱化现象十分突出，它们有一系列森林种、草原种和荒漠种及相关的形态变异。用锦鸡儿属植物进行青藏高原和喜马拉雅区域内的分布区关系分析及最小生成树MST和特有性简约性分析(PAE)，表明横断山地区特别是其北部是本属植物的一个地理结点。以此沿横断山向北部唐古特和西部藏东南适应性辐射。横断山和西喜马拉雅联系微弱，看不出植物长距离扩散的踪迹，大多是由于生态因子限制而产生的隔离。虽然本区不可能是锦鸡儿属的起源地，然而，通过本区与邻近地区的地理联系，可推测它们在我国适应性辐射方向是从东北向西南。结合豆科蝶形花亚科其它属化石记录及其分布区局限在温带亚洲等现象，认为锦鸡儿植物是一组特化、晚近衍生的类群，起源于北方东西伯利亚晚第三纪中新世后期至上新世。

THE GEOGRAPHIC DISTRIBUTION OF THE GENUS CARAGANA IN QINGHAI-XIZANG PLATEAU AND HIMALAYAS

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 vi-carism is mainly influenced by some ecological factors such as climate and vegetation . Ser. Bracteolatae Kom. , including five species, forms a vicarism example along the Hengduan Mountains 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.