Asian Begonia: out of Africa via the Himalayas?
Begonia, biogeography, China, Himalayas, molecular phylogeny, southeast Asia
The large genus Begonia began to diverge in Africa during the Oligocene. The current hotspot of diversity for the genus in China and Southeast Asia must therefore be the result of an eastward dispersal or migration across the Asian continent. To investigate the role of the Himalayas as a mesic corridor facilitating this migration, we constructed a time- calibrated molecular phylogeny using ITS sequence data. Himalayan species of Begonia were found to fall into two groups. The first is an unresolved grade of tuberous, deciduous species of unknown geographic origin, with evidence of endemic radiations in the Himalayan region beginning c. 7.4 Ma, coinciding with the onset of the Asian monsoon. The second is a group of evergreen rhizomatous species with a probable origin in China, which immigrated to the Himalayan region c. 5.1 Ma, coinciding with an intensification of the monsoon. The hypothesis of the Himalayas being a mesic migration route during the colonisation of Asia is not refuted, but further data is needed.