Evolution of the platycodonoid group with particular references to biogeography and character evolution

Abstract

The Qinghai-Tibet Plateau (QTP) is an important center of origin and diversification for many northern temperate plants. The hypothesis "out-of-QTP" suggests that the majority of northern temperate plants have originated and dispersed from the QTP and adjacent regions. An interesting question is whether the biogeographic history of the platycodonoids (Campanulaceae), a group mainly distributed in the QTP and adjacent regions, coincides with the hypothesis "out-of-QTP"? Furthermore, how have the diagnostic characters of the platycodonoids evolved? In the present study, all 10 genera of the platycodonoids were sampled for molecular phylogeny and dating analyses, and ancestral states of distribution and characters were reconstructed. The results do not support the platycodonoids as an "out-of-QTP" group, but instead they might have descended from Tethyan ancestors. The dispersal and diversification of the platycodonoids in Asia might have been driven by the uplift of the QTP. The present study highlights the importance of the Tethyan Tertiary flora for the origin of the Sino-Himalayan flora and the influence of the uplift of QTP on diversification of northern temperate plants. In addition, character state reconstruction reveals that the inferior ovary, capsule, long-colpate pollen, and chromosome number 2n = 14 are probably ancestral states.