More miocene dispersal between Africa and Asia-the case of Bridelia (Phyllanthaceae)

Several hundred angiosperm genera range from Africa to Asia and Australia, among them Bridelia (Phyllanthaceae), with ca. 40 species, including commercially important timber trees. We here use nuclear and chloroplast DNA sequences from herbarium material, plus new collections from China, to test the monophyly of Bridelia and to infer the geologic times when it acquired its disjunct range. For the Southeast Asian mainland, within-species sampling, including material collected close to the type localities, allowed testing current species concepts. Based on a sample of 114 chloroplast matK sequences of Phyllanthaceae, Bridelia is monophyletic and sister to an Asian clade which requires resurrecting an older generic name to make the African Cleistanthus monophyletic. Within Bridelia, gene trees from the combined data (3,177 aligned nucleotides from 25 species of Bridelia plus outgroups) agree with most morphological species boundaries. Exceptions are that B. tomentosa must include B. harmandii and B. curtisii to become monophyletic and that B. fordii is distinct from B. retusa. The topology, together with relaxed clock divergence times, implies that Bridelia dispersed from tropical Asia to Africa once or twice between 10 and 1.85 million years ago (Ma). Australia was reached, probably from New Guinea, at least twice, both times ca. 2 Ma. Together with earlier studies, there are now at least eight cases of Neogene long distance dispersal between Africa and Asia (followed by speciation), with no directional bias apparent so far.