Phylogenetic position of the South American dioecious genus Hamadryas and related Ranunculeae (Ranunculaceae)

The endemic southern South American genus Hamadryas (Ranunculaceae), consisting of five species, has been regarded as closely related to or part of Ranunculus s.l. (tribe Ranunculeae) based on morphological observations. However, it differs from most other Ranunculus in its dioecious breeding system. Its phylogenetic placement within Ranunculaceae has never been rigorously examined. Here we report the results of two DNA sequence analyses: one using the chloroplast genes atpB and rbcL to broadly place Hamadryas within the family; the second using nuclear ribosomal internal transcribed spacer (ITS) regions to further pinpoint Hamadryas's position within Ranunculeae. The chloroplast data confirm a monophyletic Ranunculoideae consisting of Ranunculeae and Anemoneae, with a well-supported rooting for Ranunculeae between a clade consisting of Hamadrayas, Halerpestes, and Trautvetteria (also including Ranunculus ficaria, but with weak support) and a core Raununculus clade. With the ITS data for Ranunculeae, Hamadryas is within a moderately supported clade consisting of Oxygraphis (Asia, Alaska), Peltocalathos (South Africa), and Callianthemoides (Chile, Argentina), with Callianthemoides weakly supported as sister to Hamadryas. Based on this and other data, we recommend that Hamadryas (along with many other segregate genera within Ranunculeae) be subsumed within the genus Ranunculus. We characterize the morphology and other attributes that occur in Hamadryas and sister genera and discuss possible causes for the development of dioecy in Hamadryas.