Macroevolutionary patterns of floral diversification

Since crown group angiosperms originated more than 140 Mya., flowers have diversified into a multitude of floral forms. Their diversification was shaped by the combination of extrinsic physical (e.g., climate) and biological (e.g., pollinators) factors as well as by their intrinsic structural and genetic constraints. The continuing progress in phylogenetic and phylogenomic analyses in angiosperms, together with results from comparative floral development and morphology, provide a unique opportunity to understand macroevolutionary patterns of floral diversification. In this study, we trace the evolution and diversification of various floral traits related to the three main organ categories (perianth, androecium, and gynoecium) and key aspects of floral structure (e.g., merism, phyllotaxis, and union of organs). We base our analyses on an extensive, referenced and continuously updated and curated dataset of floral morphology, which we compiled over the past decade in the collaborative database PROTEUS, as part of the eFLOWER initiative. The current dataset comprises 30 floral traits scored for 1201 species, representing all currently recognized angiosperm families. We apply ancestral state reconstructions using parsimony, maximum likelihood, and Bayesian inference, exploring different evolutionary models, to trace the evolution and diversification of pivotal floral traits. In addition, we reconstruct and re-evaluate ancestral flowers at the crown node and additional deep nodes in the angiosperm phylogeny. We find that floral diversification was shaped both by modification and innovation and that similar evolutionary trajectories were often explored repeatedly and independently in different parts of the angiosperm phylogenetic tree. Our study complements earlier and ongoing studies from the fields of paleobotany, comparative morphology, and evo-devo in their attempts to answer key questions on the early evolution and diversification of flowers in angiosperms.