CHEMOTAXONOMY OF CYNANCHUM AND ITS ALLIED GENERA WITH NOTES ON THE GENERIC CHARACTERISTICS OF VINCETOXICUM
Qiu Shengxiang, Li Dezhu, Zhang Zhuangxin, Zhou Jun, Wu Zhengyi(C. Y. Wu) (Kunming Institute of Botany, Academia Sinica, Kunming)
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 C211steroidal 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 skeleton (skeletons B, C, and D). Based on this and other scientists' work, we put forth the plausible biogenetic pathway of the C2I 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 Vincetoxicum Wolf as a section of Cynanchum, but they also admitted that their treatment must be revised when new evidences of cytology, chemistry and palacobotany are found. The chemotaxonomical study on these genera have already provided taxonomists with .some important information. As showed in tab. 2, we know that the two basic types of aglycones skeleton have a close relation to the root-type, habit of the sections of Cynanchum sensu Tsiang et P. T. Li. Also with the support of these evidences, some new ideas for the taxonomy of Cynanchum arc given. The genus Vincetoxicum, of being fibrous root-type, erect habit, single corona and the informal skeleton of C21 steroidal aglycone, is different from Cynanchum, with tap root-type, twining habit, double coronaYand the formal skeleton aglycone. The taxonomical treatments, based on this, are given. Among which there are 15 new combinations, 1 new status et combination, and 1 new status.