Darwin’s second ‘abominable mystery’: trait flexibility as the innovation leading to angiosperm diversity

Abstract

The fact that angiosperms are so species-rich and ecologically diverse - Darwin's second abominable mystery - could be explained by their ability to 'reinvent' themselves by evolving functional traits repeatedly over time, space and taxonomic clades. These trait innovationsmay facilitate adaptation andincreasediversification rates.In this article, I quantify this 'trait flexibility' by reviewing the literature on trait transition rates and trait-dependent diversification rates in angiosperms and their extant sister clade, acrogymnosperms. I showthat angiosperms indeed evolved elevated trait transition and trait-dependent diversification rates compared to gymnosperms, and rates are highest within species-rich angiosperm orders (e.g. Fabales, Lamiales). The (genetic) ability of certain angiosperm lineages to repeatedly evolve adaptive traits may have facilitated sustained high net diversification resulting from numerous episodic radiations.