Key innovations within a geographical context in flowering plants: towards resolving Darwin's abominable mystery.

Elucidating factors associated with diversification have been attempted in lineages as diverse as birds, mammals and angiosperms, yet has met with limited success. In flowering plants, the ambiguity of associations between traits and diversification has sparked debate since Darwin's description of angiosperm diversification as an 'abominable mystery'. Recent work has found that diversification is often diversity-dependent, suggesting that species richness depends on geographical area available more than on traits or the time available to accumulate species. Here, we undertake phylogenetic generalized least squares analyses that jointly examine the effects of age, ecoregion area and four ecological traits on diversification in 409 angiosperm families. Area explained the most variation, dwarfing the effect of traits and age, suggesting that diversity-dependent diversification is controlled by ecological limits. Within the context of area, however, traits associated with biotic pollination (zygomorphy) exhibited the greatest effect, possibly through the evolution of specialization.