Splitting Echinocactus : morphological and molecular evidence support the recognition of Homalocephala as a distinct genus in the Cacteae

Molecular phylogenetic studies of the six currently accepted species in the genus have partially clarified certain aspects of its phylogeny. Most of the studies lack a complete sampling of and are based only in one source of data. Phylogenetic uncertainties in , such as the recognition of as a different genus from , the exclusion of or the affinities of , are here resolved. Phylogenetic relationships of were reconstructed with a maximum parsimony, a maximum likelihood and a Bayesian approach including 42 morphological characters, four chloroplast markers ( B- L, H- A, L- F and ) and two nuclear genes. The utility of these two nuclear regions related to the betalain cycles (DODA and ) are explored and discussed in relation to their potential as phylogenetic markers. Concatenated analyses with morphological and molecular data sets, plus 13 indels (2847 characters and 26 taxa), show general agreement with previous independent phylogenetic proposals but with strong support in order to propose the recognition of a reduced and the recognition of at the generic level. These results recovered a polyphyletic as currently defined. The here-named HEA clade, recovers the species of , and as a monophyletic group with strong internal support. The ( and ), was recovered as sister to the clade ( and ), plus the clade. Consequently, we propose here to recognise a monophyletic and a monophyletic as two distinct genera with their own molecular and morphological synapomorphies. The evolution of some morphological characters supporting these clades are discussed, the necessary new taxonomic combinations for are proposed and an identification key for the genera, the species and the subspecies of the HEA clade are presented.