de Sa, R.O. and D.M. Hillis (1990). Phylogenetic relationships of the pipid frogs Xenopus and Silurana: an integration of ribosomal DNA and morphology. Mol. Biol. Evol. 7 (4): 365-376. The genus Silurana was resurrected by Cannatella and Trueb (1988) to accomodate the species in the Xenopus tropicalis group. Cannatella and Trueb (1988) believed the members of the Xenopus tropicalis group were more closely related to Hymenochirus, Pipa, and Pseudhymenochirus than they were to to other species of Xenopus. de Sa and Hillis (1990) refuted this phylogenetic placement of the Xenopus tropicalis group; instead, they found that Xenopus tropicalis and Xenopus epitropicalis were more closely related to other Xenopus than to Hymenochirus, Pipa, and Pseudhymenochirus. de Sa and Hillis also noted that Xenopus tropicalis and X. epitropicalis are sister-species, forming a monophyletic group which can be recognized as the genus Silurana. Silurana and Xenopus are recognized as sister-taxa, forming the subfamily Xenopodinae. Hymenochirus, Pipa, and Pseudhymenochirus remain in the subfamily Pipinae. The Xenopodinae and Pipinae constitute the Pipidae.