Molecular phylogeny of Diplolepis (Apocynaceae-Asclepiadoideae) and allied genera, and taxonomic implications

Diplolepis, a genus from southern South America traditionally considered monotypic, has recently been shown from molecular data to include a few species that form a monophyletic group at the base of the MOG clade of Asclepiadoideae (Apocynaceae). The species transferred to Diplolepis include plants from temperate South America mostly described under the generic name "Cynanchum". Phylogenetic analyses of cpDNA trnT-trnF and rps16 sequences of 51 accessions of Asclepiadaceae using maximum parsimony and Bayesian inference methods show that all "Cynanchum" from southern Argentina and Chile (except C. atacamense), Tweedia australis and Diplolepis form a well-supported monophyletic group. Within this group, three clades are recognized: two morphologically homogeneous groups from South Andean forests and high elevation areas, and a more diverse group in flower and leaf morphology from southern South American desert and semidesert areas. The phylogenetic position of C. atacamense is equivocal but the species is transferred to Diplolepis based on morphological and biogeographical coherence. The morphological, geographical and environmental characteristics of the three recognized clades of Diplolepis are discussed and eight nomenclatural changes are proposed.