Assembly of Asian Begonia flora via the Himalayas?

Reconstructions of the phylogenetic history of Begonia show African species to be basal, with Asian and American species nested within an African grade and Asian species supported as monophyletic. The route of migration for the genus through Asia is not yet clear, but one scenario for the origin of the highly diverse SE Asian Begonia flora is an ancestral lineage migrating across the Himalayan region. This appears to be the only suitable route, given the low altitude of the bulk of the Indian subcontinent. In order to investigate the role of the Himalayan region as a mesic migratory corridor for Begonia from Africa into tropical Asia, phylogenetic relationships between 127 taxa from Nepal and Southeast Asia were investigated with a Bayesian analysis of nuclear ribosomal ITS data. The results indicate that the Nepalese Begonia flora is a complex assemblage of older lineages and very recent speciation. The role of the Himalayan orogeny and the development of a monsoon climate in the evolution of the flora will be discussed.