Phylogenetics and evolution of the Macaronesian clade of Crassulaceae inferred from nuclear and chloroplast sequence data

The Macaronesian clade of Crassulaceae comprises four genera (Aichryson, Aeon in in, Greenovia, and Monanthes) that are largely endemic to Macaronesia, a region encompassing the Azores, Madeira, and the Cape Verde, Canary and Salvage Islands. The monophyly of this clade has been supported by recent family-level phylogenetic analyses; however, the relationships within the clade remain uncertain. To resolve relationships within the Macaronesian clade, we sequenced several chloroplast DNA regions (matK and the trnL-trnF and psbA-trnH spacer regions) and the nuclear rDNA ITS region. Parsimony analyses of separate ITS and cpDNA data sets recover three major clades, corresponding to Aichryson, the perennial species of Monanthes, and Aeonium (including Greenovia). Congruence tests revealed significant heterogeneity between the ITS and cpDNA data sets. Comparison of the topologies resulting from analyses of these separate data sets indicated five instances of incongruence between the ITS and cpDNA that may be the result of cpDNA capture events. Those five cpDNA sequences that appear to be the result of hybridization were removed, and a combined cpDNA/ITS data set was constructed and analyzed. Parsimony analyses of this combined data set again resolve three major clades that correspond to Aichryson, Monanthes, and Aeonium (including Greenovia); however, the combined analyses provide greater resolution and higher internal support than the analyses of the separate data sets. Given this estimate of phylogeny, the Macaronesian clade most likely evolved from herbaceous, continental ancestors; the woody habit evolved once in Aichryson tortuosuin and again in the ancestor of the Aeonium clade. Combined analyses of cpDNA and ITS for a large sampling of the Macaronesian Crassulaceae also confirms recent conclusions that Aeonium originated in Macaronesia and not in Africa and that the east African species, A. leucoblepharum, is of recent origin and represents long-distance dispersal from Macaronesia to Africa.