We analysed 87 species of Onosma (Boraginaceae) from throughout its distribution range to investigate its evolutionary history. 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 as currently circumscribed is not monophyletic. However, the vast majority of Onosma species appear to belong to a single clade, the so‐called Onosma s.s. Outside of this core clade is a clade containing O. rostellata, a subclade of Sino‐Indian species and Maharanga emodii. Podonosma orientalis (as O. orientalis) appear only distantly related to Onosma but is more closely related to Alkanna, as also suggested in previous molecular studies. The Onosma s.s. 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, but none of these subsections was retrieved as monophyletic. We observed significant 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 suggested that the early radiation of Onosma s.l. took place at the Oligocene‐Miocene boundary and the diversification within Onosma s.s. occurred during middle to late Miocene and Pliocene.

The phylogeny of Heterocaryum and Suchtelenia was examined using sequence data from the internal transcribed spacer region of the nuclear rDNA (ITS) and plastid trnL intron and trnL–trnF intergenic spacer (trnL–F) regions. Results indicated that Heterocaryum is non-monophyletic because of the inclusion of Suchtelenia calycina (C.A.Mey.) A.DC. Heterocaryum laevigatum (Kar. & Kir.) A.DC. formed a distinct branch sister to S. calycina and remaining Heterocaryum species. Hence, all species of Heterocaryum except H. laevigatum (type species of the genus) are transferred to a new genus, Pseudoheterocaryum. Taxonomic descriptions are presented for Pseudoheterocaryum and Heterocaryum, as well as a diagnostic key to the three genera included in the present study.