The molecular phylogeny of Rebutia (Cactaceae) and its allies demonstrates the influence of paleogeography on the evolution of South American mountain cacti

The tropical Andes harbor a major part of the world's plant biodiversity. The montane cacti of the tribes Browningieae, Cereeae, and Trichocereeae underwent extensive radiation and thus are well suited as a model group to study the diversification of Andean plants. We reconstructed their phylogeny employing three noncoding chloroplast regions and explained it in the context of the geological history of South America. We found that the clade of cephalia-bearing cacti with naked pericarpels is centered in northeastern Brazil, whereas almost all other clades comprise Andean species. The spatial split between the clades was probably caused by the Andean uplift and the concurrent formation of intracontinental marine basins in the Tertiary. The phylogenetic reconstructions based on parsimony and Bayesian approaches do not reflect the traditional delimitation of the tribes and of the large genera. Our results suggest that Rebutia s.l. and Echinopsis s.l. are not monophyletic and that Sulcorebutia, Weingartia, and Cintia should be united into one genus. Even though this "Weingartia-complex" and the genus Gymnocalycium are similar in size and morphological diversity, Gymnocalycium has a very high molecular divergence suggesting a comparably older radiation.