Molecular phylogeny of selected Old World Astragalus (Fabaceae): incongruence among chloroplast trnL‐F, ndhF and nuclear ribosomal DNA ITS sequences

Abstract

This study reports maximum parsimony and Bayesian phylogenetic analyses of selected Old World Astragalus using two chloroplast fragments including trnL‐F and ndhF and the nuclear ribosomal internal transcribed spacer (nrDNA ITS). A total of 52 taxa including 34 euploid Old World and New World Astragalus, one aneuploid species from the Neo‐Astragalus clade as a representative and 14 other Astragalean taxa, plus Cheseneya astragalina and two species of Caragana as outgroups were analyzed for both trnL‐F and nrDNA ITS regions. ndhF was analyzed in 30 taxa and the same number for the combination of these three datasets were examined. In general, the trnL‐F dataset and the ndhF and nrDNA ITS datasets generated more or less the same clades within Astragalus. However, in the trnL‐F and ndhF phylogenies, Astragalus species are not gathered in a single clade, the so‐called Astragalus s.s., as indicated by the nrDNA ITS tree. Visual inspection of these three phylogenies revealed that they were inconsistent regarding the position and relationships of Astragalus hemsleyi, A. ophiocarpus, A. annularis–A. epiglottis/Astragalus pelecinus,A. echinatus and A. arizonicus. Incongruence length difference test suggested that the trnL‐F, ndhF and nrDNA ITS datasets were incongruent. In spite of this, phylogenetic analyses of the combined datasets as one unit or as three partitions generated trees that were topologically similar as a mix of the cpDNA and the nrDNA ITS trees. However, the combined dataset provided more resolved and statistically supported clades. The recently described A. memoriosus appeared closely related to A. stocksii (both from sect. Caraganella) based on both trnL‐F and nrDNA ITS sequences.