The identity of Hickenia Lillo (Apocynaceae subfam. Asclepiadoideae)

Hickenia Lillo has, until now, been treated as a monotypic genus because its corona lobes are heavily bearded adaxially (see Malme's comments quoted by Castellanos 1937: 72). Although conspicuous, this is the only floral character that separates the genus from Morrenia Lindl. Even this character is not unambiguous, as at least three species of Morrenia have pubescent patches on the adaxial face of the corona (M. brachystephana Griseb., M. odorata (Hook. & Arn.) Lindl. and M. variegata (Griseb.) T. Mey.). H. scalae (Hicken) Lillo is indistinguishable vegetatively from several species of Morrenia, and the morphology of the follicle and seeds are also typical of that genus. The close affinity of these two genera was noted by Ezcurra (1999) when she disputed the sinking of Hickenia back into Oxypetalum R. Br. in the subtribal listings of Liede (1997).