Abstract: As reported previously⁽⁸⁾, although the eighteen species of Stephania are different in chemical constituents qualitatively and quantitatively, the tubers of most species are spheroidal to obovate spheroidal in shape and hence called a common name "Shan Wu-gui" (mountain tortoise).In this paper, the morphology and histology of the underground parts of these eighteen medicinal Stephania species, viz., S. hainanensis, S. succifera, S. yunnanensis, S. viridiflavens, S. dicentrinifera, S. kwangsiensis, S. micrantha, S. epigaea, S. sinica, S. dielsiana, S. brachyandra, S. mashanica, S. tetrandra, S. excentrica, S. Cepharantha, S. japonica, S. delavayi and S. longa are described and summarized in an analytical key.