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.
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