Recurrent evolutionary changes in pollen shape and ornamentation of the vataireoid clade (Papilionoideae, Fabaceae), an early-branching lineage of florally divergent genera

Pollen traits have clarified the classification and understanding of the evolutionary history of different groups of angiosperms, due to their wide morphological diversity. To increase our knowledge on the morphological evolution of the vataireoid clade (Fabaceae, Papilionoideae), a lineage comprising 30 species of Neotropical trees in the genera Luetzelburgia, Sweetia, Vatairea and Vataireopsis, pollen materials of 26 species were acetolysed and analysed using light and scanning electron microscopy. Characters were defined to reconstruct the pollen evolution in each of the ancestral nodes of the phylogenetic tree of the clade using Bayesian stochastic character mapping. All vataireoid genera have relatively variable pollen morphology, ranging from small to medium and subtriangular to circular amb, and their aperture margo may be present or absent. The exine ornamentation varies greatly across the clade: perforate (L. praecox and S. fruticosa); rugulate (L. andradelimae); rugulate-foveolate-perforate (Vatairea guianensis and Vatairea heteroptera); reticulate (Vataireopsis araroba) and microreticulate in most species. Analyses of ancestral character reconstruction revealed multiple events of independent evolution in all pollen traits during the diversification of the vataireoid clade in the last 16 Myr, since the Miocene. Just as evolutionary transitions in floral architecture were so recurrent in the vataireoid clade, pollen evolution was relatively labile and exhibited little phylogenetic conservatism in shape or ornamentation.