Evolution on the backbone: Apocynaceae phylogenomics and new perspectives on growth forms, flowers, and fruits

Abstract

Premise of the Study: We provide the largest phylogenetic analyses to date of Apocynaceae in terms of taxa and molecular data as a framework for analyzing the evolution of vegetative and reproductive traits. Methods: We produced maximum-likelihood phylogenies of Apocynaceae using 21 plastid loci sampled from 1045 species (nearly 25% of the family) and complete plastomes from 73 species. We reconstructed ancestral states and used model comparisons in a likelihood framework to analyze character evolution across Apocynaceae. Key Results: We obtained a well-supported phylogeny of Apocynaceae, resolving poorly understood tribal and subtribal relationships (e.g., among Amsonieae and Hunterieae, within Asclepiadeae), rejecting monophyly of Melodineae and Odontadenieae, and placing previously unsampled and enigmatic taxa (e.g., Pycnobotrya). We provide new insights into the evolution of Apocynaceae, including frequent shifts between herbaceousness and woodiness, reversibility of twining, integrated evolution of the corolla and gynostegium, and ancestral baccate fruits. Conclusions: Increased sampling and selection of best-fitting models of evolution provide more resolved and robust estimates of phylogeny and character evolution than obtained in previous studies. Evolutionary inferences are sensitive to choice of phylogenetic frameworks and models.