Molecular phylogeny and Divergence times of Onosma (Boraginaceae s.s.) based on nrDNA ITS and plastid rpl32-trnL (UAG) and trnH–psbA sequences

14 November 2018

Nasrollahi, Fatemeh; Kazempour Osaloo, Shahrokh ; Mozaffarian, Valiollah ; Zare-Maivan, Hassan

In this study, we included 87 species of Onosma throughout their distribution range from Sino-India to southern Europe to investigate evolutionary history of this diverse boraginoid genus. Using nrDNA ITS and two plastid (rpl32-trnL(UAG) and trnH–psbA) markers, we reconstructed phylogenetic relationships within Onosma by conducting maximum parsimony, maximum likelihood, Bayesian, and BEAST analyses. The analyses revealed that Onosma at the current status is not monophyletic. The vast majority of Onosma species appear to belong to a single clade, the so-called Onosma s.str. External to this core is a clade containing O. rostellata, a subclade of Sino-Indian species and Maharanga emodii. Podonosma orientalis (as O. orientalis) is far distantly related to this genus and closely related to Alkanna, which is consistent with the findings of the previous molecular studies. Onosma s.str. clade includes all representatives of O. sect. Onosma, and encompasses three subsections, i.e., Onosma, Haplotricha and Heterotricha, corresponding to asterotrichous, haplotrichous and heterotrichous groups, respectively. None of these subsections was retrieved monophyletic. Our study revealed incongruence between nuclear and chloroplast phylogenies regarding the phylogenetic status of the heterotrichous group. A dozen of the Iranian haplotrichous species formed a lineage which may not hybridize with asterotrichous species. Divergence time estimates revealed that the early radiation of Onosma is inferred to have happened in the Oligocene-Miocene boundary and the diversification within Onosma s.str. occurred during middle to late Miocene and Pliocene