Molecular phylogeny and divergence times of the genus Hedysarum (Fabaceae) with special reference to section Multicaulia in Southwest Asia

A total of 93 species of Hedysarum from diverse biogeographic regions, in particular from southwest Asia, were included in phylogenetic analyses using nuclear (ITS) and plastid DNA sequences (trnL-trnF and matK). Maximum likelihood and Bayesian analyses of combined plastid data retrieved Hedysarum as monophyletic, whereas phylogenetic analyses of the nuclear data inferred Hedysarum as non-monophyletic. In both datasets, Hedysarum comprised three distinct and well-supported clades corresponding to sections Hedysarum, Stracheya and Multicaulia. The latter section fell into two distinct lineages, taxonomically redefined as H. subsects. Multicaulia and Crinifera. Thus, our results did not support the monophyly of the three traditionally recognized subsections of Multicaulia. Furthermore, within H. subsect. Crinifera, several species groups were recognized. Bayesian divergence time estimation suggested that the initial radiation of Hedysarum and the subsequent divergence of its major clades started in the middle Miocene and extended into the Pliocene and Pleistocene. Based on the molecular phylogenetic results, an updated taxonomic treatment is provided for H. subsects. Multicaulia and Crinifera as well as for H. sect. Stracheya expanded to include H. tibeticum plus four species traditionally placed in H. subsect. Subacaulia. For species of H. sect. Stracheya, a determination key is given.