Towards a phylogeny for Astragalus section Caprini (Fabaceae) and its allies based on nuclear and plastid DNA sequences

Abstract

We conducted phylogenetic analyses of the sect. Caprini and its closely related sections within Astragalus. Analyses of a combined dataset including nrDNA ETS and three cpDNA markers using maximum parsimony and Bayesian inference from 44 species of sect. Caprini and its allied taxa yielded congruent relationships among several major lineages. These results largely disagree with previously recognized taxonomic groups, most notably in the following ways: (1) subsects. Caprini and Purpurascentes of sect. Caprini are not natural groups; (2) sects. Alopecuroidei and Laxiflori are nested within sect. Astragalus; and (3) subsect. Chronopus constitutes a separate phylogenetic lineage. Representatives of sects. Astragalus, Alopecuroidei, and Laxiflori share a common ancestor with that of sect. Caprini. Our studies indicate that Astragalus annularis is an outlier species for the genus Astragalus and sect. Caraganella is the first-diverging clade within the genus Astragalus. Results of these analyses are supported by morphology and suggest the need for new taxonomic delimitations, which are forthcoming. Key morphological characters were mapped onto the phylogenetic tree and discussed.