A phylogenetic study of Echidnopsis Hook. f. (Apocynaceae-Asclepiadoideae) - taxonomic implications and the colonization of the Socotran archipelago

We investigated the phylogeny, taxonomy and biogeography of the Eritreo-Arabian genus Echidnopsis Hook. f. (Apocynaceae-Asclepiadoideae). Phylogenetic reconstructions based on nrITS sequence data were obtained using maximum likelihood and parsimony analyses. The results reveal two weakly supported clades, each with a mix of African and Arabian taxa, including the genus Rhytidocaulon, and with four Socotran species forming a subclade of their own. Rather than a vicariance origin of these island elements, our data suggest a single dispersal event from eastern Africa. Echidnopsis thus parallels biogeographic patterns found for other Socotran endemic plants. Our revised taxonomy recognizes 28 species and 4 subspecies in the genus. Two new combinations, E. planiflora subsp. chrysantha and E. sharpei subsp. bavazzani are proposed.