Phylogeny, biogeography and divergence times of Astragalus section Incani DC. (Fabaceae) inferred from nrDNA ITS and plastid rpl32-trnL(UAG) sequences
19 September 2018
Amini, Elham; Kazempour Osaloo, Shahrokh ; Maassoumi, Ali Asghar; Zare-Maivan, HassanSection Incani, one of the most species-rich sections of Astragalus with ca 140 species, is well known for its taxonomic complication as a result of overlapping morphological characters and high phenotypic plasticity. Its main centers of diversity are Iran and Turkey with about 120 species. This is the first comprehensive work on the section Incani, representing the full range of geographical distribution. Using nrDNA ITS and plastid rpl32-trnL(UAG) markers, we reconstructed phylogenetic relationships, conducting maximum parsimony, maximum likelihood, Bayesian, Beast and S-DIVA analyses. All members of section (with the inclusion of A. subsecundus), except for A. platyphyllus formed a well-supported clade (Incani s.s.). Two major groups were detected, reflecting the biogeographical distribution of Incani s.s. One group includes nine examined species restricted to eastern Iran and Central Asia and the next group comprises the majority of species from west and northwestern Iran, Turkey and southern Europe. The Divergence time analysis reveals Incani s.s. presumably originated at the late Pliocene and majority of speciation events to the last 1-1.5 Myr. Dating analysis indicated the recent diversification of Incani s.s. coincides with climate modifications during the Pliocene and Pleistocene followed with a complex biogeographical history in which dispersal have been vital in the shaping of the current distribution pattern in Incani s.s. The S-DIVA suggests a probable east–west pattern of dispersal and a major phylogenetic split between eastern and western lineages and possibility of the eastern origin. The geographical distribution of A. monspessulanus/A. incanus and A. ackerbergensis/A. gueldenstaedtiae does not correspond to their phylogenetic status. The former species are restricted to southern Europe/North Africa, placed in two distinct subclades. The latter, restricted to northeastern Iran were intermingled with species of western and northwestern Iran and Turkey. Astragalus sykesiae was resurrected as a distinct species separated from a broadly defined A. mercklinii.