From to (Annonaceae): transfer of species enlarges a previously monotypic genus.

The genus Chaowasku (Annonaceae) was a poorly known monotypic genus from Vietnam that was recently segregated from the highly polyphyletic genus s.l. The sister clade relationship between and was not well established in previous study. The phylogenetic position of two spp. from China, S.K.Wu ex P.T.Li and C.Y.Wu ex P.T.Li, remains unresolved and is shown here to be phylogenetically affiliated with . Phylogenetic analyses of six chloroplast regions (K, F, A-H, L, L-F and 1; ca.7.3 kb, 60 accessions) unambiguously placed and in the same clade with (PP = 1, MPBS = 97%); the entire clade is sister to with weak to strong support (PP = 1, MPBS = 54%). and share several diagnostic characters with , including the raised midrib on the upper surface of the leaf , conspicuous foliar glands when dried, petiole with transverse striations when dried and axillary inflorescences. The two species differ from in having fewer flowers per inflorescence, longer linear petals and two ovules per carpel. On the basis of the combined molecular phylogenetic and morphological data, we propose two new combinations, (S.K.Wu ex P.T.Li) B.Xue & Y.H.Tan and (C.Y.Wu ex P.T.Li) B.Xue & Y.H.Tan. The protologue of did not include a description of the flowers, which we provide here. An updated description for the genus and a key to species in the genus is also provided.