Systematics of Alhagi: molecular phylogeny and morphology revisited

Alhagi is a small genus of desert or semi-desert shrubs with about six species widely distributed throughout northern Africa, eastern Mediterranean, the Middle East to the Central Asia, and small parts of India and China. Despite previous molecular and morphological studies on the genus, the taxonomy of Alhagi has been remained controversial. In order to delimit natural groups as well as to clarify interspecific relationships of Alhagi species distributed in Iran, 45 ingroup taxa representing 30 accessions of the genus Alhagi and 15 species from the sister genera, as well as two species, namely, Astragalus arthuri and Colutea persica as outgroups were selected. The nuclear ribosomal DNA internal transcribed spacer was employed for phylogenetic reconstructions. Phylogenetic analyses were performed using maximum parsimony, maximum likelihood and Bayesian inference. The obtained results recovered Alhagi accessions as a well-supported monophyletic group. All three traditionally recognized species in Iran split into two distinct morphologically well-supported lineages similar to splits graph. The results showed that, Alhagi maurorum and A. graecorum are recognized as two distinct species distributed in two phytogeographical regions of Irano-Turanian and Saharo-Sindian. As a complementary taxonomic treatment, the diagnostic key and description of the species are also provided herewith.