Tertiary montane origin of the Central Asian flora, evidence inferred from cpDNA sequences of Atraphaxis (Polygonaceae).

Atraphaxis has approximately 25 species and a distribution center in Central Asia. It has been previously used to hypothesize an origin from montane forest. We sampled 18 species covering three sections within the genus and sequenced five cpDNA spacers, atpB-rbcL, psbK-psbI, psbA-trnH, rbcL, and trnL-trnF. BEAST was used to reconstruct phylogenetic relationship and time divergences, and S-DIVA and Lagrange were used, based on distribution area and ecotype data, for reconstruction of ancestral areas and events. Our results appear compatible with designation of three taxonomic sections within the genus. The generic stem and crown ages were Eocene, approximately 47 Ma, and Oligocene 27 Ma, respectively. The origin of Atraphaxis is confirmed as montane, with an ancestral area consisting of the Junggar Basin and uplands of the Pamir-Tianshan-Alatau-Altai mountain chains, and ancestral ecotype of montane forest. Two remarkable paleogeographic events, shrinkage of the inland Paratethys Sea at the boundary of the late Oligocene and early Miocene, and the time intervals of cooling and drying of global climate from 24 (22) Ma onward likely facilitated early diversification of Atraphaxis, while rapid uplift of the Tianshan Mountains during the late Miocene may have promoted later diversification.