Allopolyploidy, diversification, and the Miocene grassland expansion

Duplication of genomes following hybridization (allopolyploidy) is common among flowering plants, particularly in the grasses that cover vast areas of the world and provide food and fuel. Here, we find that genome duplication has occurred at a remarkable rate, accounting for at least a third of all speciation events in a group of about 1,200 species. Much of this genome duplication occurred during the expansion of the C₄ grasslands in the Late Miocene. We find no evidence that allopolyploidy leads directly to a change in the net rate of diversification or correlates with the origin of novel morphological characters. However, as a mode of speciation, the frequency of allopolyploidization is surprisingly high.