An updated plastome phylogeny and molecular dating of Apocynaceae, with an emphasis on histories of biogeography and diversification in tropical and subtropical Asia

Abstract

Investigating the evolutionary history and species diversification patterns in hyperdiverse lineages is essential for understanding how species diversity accumulates and how floras assemble historically across diverse regions. A large angiosperm family, Apocynaceae, exhibited remarkable diversity in functional traits including growth form, fruit types, and pollen aggregation, which may have a substantial impact on species diversification rates. However, the lack of a robust and well dated phylogeny has hindered our understanding of Apocynaceae diversification. To address this gap, we reconstructed a robust phylogeny covering 22 of 25 tribes using plastome sequences, then employed this framework to estimate divergence times, analyze diversification patterns, and investigate associations between species diversification and functional traits. The plastome phylogenies received strong nodal support across most branches. Among higher taxonomic groupings, three subfamilies (Asclepiadoideae, Secamonoideae, and Periplocoideae) were monophyletic. At the tribal levels, 19 tribes were strongly supported as monophyletic except Melodineae, Willughbeieae, and Vinceae. Additionally, five genera (Vincetoxicum, Cynanchum, Hoya, Marsdenia, and Aganosma) were identified as nonmonophyletic. Our analyses revealed that Apocynaceae originated in the paleotropics during the middle Late Cretaceous. Integrating binary state speciation and extinction (BiSSE), hidden state speciation and extinction (HiSSE), and fast, intuitive state-dependent speciation-extinction (FiSSE) analyses, we found that species with pollinia had a higher speciation rate than those without. Dry-fruited species had a higher speciation rate than those with fleshy fruits. Furthermore, Bayesian analysis of macro-evolutionary mixtures (BAMM) detected a diversification rate increase coinciding with the evolution of pollinia with clip-type attachment mechanisms in the subfamily Asclepiadoideae. Herbs had the highest speciation rate, followed by climbers and self-supporting species. Our findings contribute to understanding the historical assembly of floras in tropical and subtropical Asia.

Keywords

Apocynaceae / biogeography / plastid phylogenomics / pollinia / Southeast Asia / species diversification

RIGHTS & PERMISSIONS

2025 Institute of Botany, Chinese Academy of Sciences.