Abstract: Abstract This paper deals with the taxonomical problems of the genus Cynanchum and its allied genera. So far the constituents of 17 species in these genera have been studied. We summarized the constituents, especially the C21 ste-roidal constituents, among which there are 46 C21 steroidal glycosides and 47 steroidal aglycones, of these genera. We classify these aglycones into two basic types of skeletons, i. e. the formal skeleton (skeleton A) and the informal skele-ton (skeletons B, C, and D). Based on this and other scientists' work, we put forth the plausible biogenetic pathway of the Cgi steroidal aglycone. Cynanchum Linn. is a 'difficult taxon' in Asclepiadaceae. E. G. Pobedimova (1953, 1973) , M. Kitagawa (1940, 1959) , K. H. Rechinger (1970) , F. Markgraf (1971) and H. K. Airy Shaw (1973) treated it as several different genera, including Vincetoxicum Wolf. But other taxonomists thought that it is a separate genus. Prof. Tsiang Ying et Li Ping-to (1974, 1977) dealt with Vince-toxicum Wolf as a section of Cynanchum, but they also admitted that their trea-tment must be revised when new evidences of cytology, chemistry and palaeobotany are found.

Key words: Cynanchum

摘要： 本文讨论了鹅绒藤属及其近缘属的分类问题。根据这类植物所含的C21甾体甙元结构类型的分类，生源合成途径假说，以及C21甾体甙元的分布，结合形态学的比较分析和其它证据，认为Vincetoxicum是一个脱胎于Cynanchum，但又较之进化的自然类群，应恢复其属级地位。列举了国产白前属全部分类群的正确学名，其中包括15个新组合，1个改级新组合和1个新改级。

关键词: 鹅绒藤属, 白前属。C21甾体甙元, 生源合成, 化学分类