Temporal diversification in the genus Onosma (Boraginaceae) based on nuclear and plastid DNA sequences

The genus Onosma is a homogeneous taxon with high morphological variation and due to the similarities among the Onosma taxa, there are many problems in their identification. Hence, systematically and taxonomically, it is considered a difficult genus. In the present study, we included a large number of Onosma species throughout their distribution range. Using nuclear (ITS) and two plastids (rpl32-trnL(UAG) and trnH-psbA) markers, we analyzed the evolutionary history, divergence time and diversification patterns of Onosma across the tropical, subtropical and temperate regions. Divergence time estimates suggest the early radiation of Onosma s.l. happened at the Oligocene-Miocene boundary. BAMM analyses indicate that the best configuration included one significant shift in diversification rates within Onosma: on the branch leading to the clade comprised of species of confined to Iran.