Evolution of stamen dimetrism in Melastomataceae, a large radiation of pollen flowers

•Changes in floral traits across evolutionary time are expected in response to selective pressures imposed by pollinators.•Stamen dimetrism represents an important strategy to decrease pollen loss during bee-flower interactions in pollen flowers.•Stamen dimetrism is a labile trait, appeared several times throughout the Melastomataceae evolutionary history.•Our data suggest that plants that rely on pollinators to reproduce have evolved larger flowers with greater stamen dimetrism.•The dependence on pollinators for reproduction has probably contributed to the maintenance of the buzz pollination. Changes in floral traits across evolutionary time are expected in response to selective pressures imposed by pollinators. Stamen dimetrism (here defined as size differences between stamens within the same flower) represents an important strategy to decrease pollen loss during bee-flower interactions in pollen flowers. However, the evolutionary history of stamen dimetrism, and the links between this and other reproductive traits across long periods of time are still poorly understood. Here we investigate the evolution of stamens dimetrism and the evolutionary correlation of this trait and other floral structures and reproductive strategies in Melastomataceae. Floral traits were scored from 336 species and reproductive biology data was gathered for 81 species. Stamen dimetrism is a labile trait, appeared several times throughout the evolutionary history of this clade and is evolutionarily correlated to floral size. Among the 81 species analyzed, we observed that the lineages that depend on pollinators to reproduce correspond to those that evolved the highest stamen dimetrism. The evolutionary lability of stamen dimetrism has probably contributed to the maintenance of the buzz pollination adaptive plateau in possibly the largest radiation of pollen flowers in angiosperms.