Apocynaceae is one of the ten largest families of flowering plants, and is a key component of biodiversity hotspots in Southeast Asia and southern Africa. Because of a limited fossil record and insufficient sampling, especially of Asian species, it is difficult to understand its evolutionary timeline and diversification patterns.

In a study published in Journal of Systematics & Evolution, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences (CAS) and Kunming Institute of Botany of CAS reconstructed the phylogenetic tree of the Apocynaceae family, and sought to resolve the issue of uncertainties in the classification and evolutionary history of this ecologically and economically important plant family.

Researchers built a high-resolution phylogeny using plastid coding sequences, and performed molecular dating analyses with four key Apocynaceae macrofossils as calibration points.

Plastome-based phylogeny confirmed three subfamilies as monophyletic, consistent with modern classification systems. Three tribes and five genera were identified as non-monophyletic, indicating a need for future taxonomic revisions. Molecular dating analyses, incorporating recent fossil discoveries, showed that Apocynaceae originated approximately 87.57 million years ago in the paleotropics.

Furthermore, researchers investigated the association between species diversification and functional traits in Apocynaceae family. They found that species with pollinia (cohesive pollen packets) showed a higher speciation rate than those without, and that dry-fruited species diversified faster than those with fleshy fruits. Among different growth forms, they found that herbs exhibited the highest speciation rate, followed by climbers, and self-supporting trees and shrubs had the lowest.

"By constructing a more complete phylogenetic tree of Apocynaceae, we not only clarify the family's complex relationships and ancient origin, but also provides evidence that the evolution of pollinia and dry fruits are key factors driving the species richness," said YU Wenbin from XTBG.