Diversification of Cynoglossinae genera (Cynoglosseae-Boraginaceae) in the western Irano–Turanian bioregion

Abstract

The Irano–Turanian (I–T) bioregion harbours one of the Old World’s greatest repositories of botanical diversity; however, the diversification patterns and the phenotypic evolution of its flora are sorely understudied. The subtribe Cynoglossinae is characteristic of the western I–T bioregion, species-rich in both the desertic lowlands and the more mesic highlands of the Iranian plateau. About 70 species of Cynoglossinae are present in the Iranian plateau, 47 of which are endemic to the plateau. Herein, nuclear internal transcribed spacer sequences as well as cpDNA rpl32-trnL and trnH–psbA sequences were used to investigate the molecular phylogeny, historical biogeography, and ancestral character states of Cynoglossinae. Molecular dating and ancestral range reconstruction analyses indicated that the subtribe Cynoglossinae has initiated its diversification from the eastern part of the western I–T during the mid-Miocene, concomitantly with the uplift of the Pamir and Hindu Kush mountains. Moreover, from the Pliocene onwards, the Afghan–India collision and extensive deformation of the Arabia–Eurasia convergence likely promoted allopatric speciation in Cynoglossinae via mostly vicariance events. Evolution of annuals with small nutlets from perennials with large nutlets was accompanied by mesic to desert habitat shifts. Herein, to explain distribution of Cynoglossinae in the western I–T, the congruence between cladogenetic, geological, and palaeoclimatic events was investigated.