Dated Phylogeny of Astragalus Section Stereothrix (Fabaceae) and Allied Taxa in the Hypoglottis Clade.

The subgenus Bunge, which consists of several sections, is one of the taxonomically most complicated groups in the genus. The section Bunge belongs to this subgenus and is a significant element of the Irano-Turanian floristic region. A molecular phylogenetic analysis of this section and its closely related taxa using nuclear ribosomal DNA internal transcribed spacers (ITS) and external transcribed spacer (ETS) regions as well as plastid K sequences were conducted. Parsimony analyses and Bayesian phylogenetic inference revealed that the section is not monophyletic in its current form, as some taxa belonging to closely related sections such as DC. and the Bunge group within the sect. render it paraphyletic. Moreover, species groups belonging to sect. are placed in different clades within the phylogenetic tree of subgenus , which indicates polyphyly, i.e., multiple independent origins of taxa placed in the sect. . Molecular dating of the group estimated an age of 3.62 (1.73-5.62) My for this assemblage with the major diversification events happening during the last 2 My. Many species groups separated only within the last 0.5 to 1 My. Based on morphological and molecular data, we discuss the phylogenetic relationships of the groups and synonymy of species. In addition, the included taxa of sect. are not monophyletic and include species belonging to sects. , , , and group within the sect. taxa. We conclude that only an analysis including all groups and nearly all species of the sections within the Hypoglottis clade can finally result in an new evolutionary-based system for these taxa.