Abstract: The crude drug Bai-Jiang-Cao specified in the Chinese Pharmacopoeia 1977 edition consists of the dried whole plants of Patrinia scabioaaefolia Fisch. or P. villosa Juss., family Valerianaceae. However, other plants of the genus Patrinia as well as plants of the families Cruciferae and Compositae are also used as Bai-jiang-cao in certain districts in China. In this paper, the results of comparative morphological and histological studies of eight Patrinia species, viz. P. scabiosaefolia Fisch., P. villosa Juss., P. scabra Bunge, P. heterophylla Bunge, P. rupestris (Pall.) Dufr., P. angustifolia Hemsl., P. monandra C. B. Clarke and P. diandra Kitagawa, are described and illustrated with line drawings. Separate keys for the identification of aerial and underground portions of the drugs are presented. The site of cork formation as well as the formation and development of the parenchymatous band in the rhizomes of certain Patrinia species are discussed. The specimens of Patinia diandra Kitagawa collected in Yanqing, Beijing, were found to be identical macroscopically but different in several microscopical characters with that collected in Laotieshan, Liaoning Province, the habitat of the typespecimen.