The members of the S. tani complex can be distinguished from other species of the S. tuberosum group by the roundish margins of the postgenal cleft (Fig. 3 F, G) and ventral tubercles of the larva, short terminal spines (Fig. 8) of the pupa, absence of a pair of clustered hairs on sternite VII in the female, and a narrow median sclerite in the male (Fig. 9 D). Structural variation within each of the nine cytoforms is typically as great as it is among cytoforms (Table 1), with one exception. The pupa of cytoform H has a lower density of cephalic microtubercles (Fig 5 B) and a longer ventralmost gill stalk (Fig. 7 F) than do other cytoforms in the complex. Variation in meristic characters among cytoforms, such as the number of primary rays in the labral fan, probably is related to habitat (Zhang & Malmqvist 1997). Some of the cytoforms of the S. tani complex might prove to be valid species. Cytoform B or D, because of geographical location, probably represents true S. tani, which was described from Malaya.