The botanical origins of Cynanchum species (Cynanchum spp.) on the Taiwan market have been established by histological studies in the present paper. The results showed that the Chinese crude drug Pai-wei on the Taiwan market was derived from the dried roots of Cynanchum atratum Bunge; that of Pai-chein was derived from the dried roots of C. stauntonii (Decne.) Hand.-Mazz; and the Wanling-shu used locally in Taiwan was derived from the dried roots of C. taiwanianum Yamazaki.