Diversification and fruit evolution in eumalvoids (Malvaceae)

Morphological innovations associated with more efficient seed dispersal have often been considered as drivers for the diversification of angiosperm lineages, but studies testing this relationship are relatively few and have led to differing results. In this study, we explore the evolution of the fruit and its role in the diversification of eumalvoids (Malvaceae). Almost two-thirds of the species in this group have schizocarps, which exhibit various adaptations to a more efficient dispersal compared to capsules. Schizocarp with a high number of carpels characterizes Malveae, the most species-rich tribe in the eumalvoid clade. We estimated the diversification rates across this clade and tested whether the two traits (the schizocarpic fruit and an increased number of carpels) were correlated with speciation and net diversification rates in the group. The analyses revealed that Malveae diversified at higher rates than the remainder of the eumalvoids, with an abrupt acceleration occurring between 30 and 40 Mya. The schizocarpic fruit and the high number of carpels are correlated with increased speciation rates, suggesting that both traits contributed to the success of the eumalvoids and especially of Malveae. These traits would have allowed the successful exploitation of open, arid ecosystems that accompanied the Eocene/Oligocene boundary. The analyses also showed that the transition to the schizocarpic condition is irreversible, which also helps to explain its predominance in Malvoideae.