The Primulaceae, a family of about 1300 species of primarily shrubs and small trees, are well represented in the Madagascar region and the more inclusive lands within and around the Indian Ocean. The study of their biogeographical history thus affords an excellent opportunity to assess the underlying history of dispersal and diversification events that have shaped plant diversity in Madagascar and neighbouring islands.

Dr. Joeri Strijk, a postdoc of Xishuangbanna Tropical Botanical Garden (XTBG), led a study to reconstruct the historical biogeography of Indian Ocean Primulaceae. They used a dataset that included multiple molecular markers, fossil calibration points, all species of Mascarene Badula and a subset of Madagascan Oncostemum to reconstruct the historical biogeography of Indian Ocean Primulaceae. They placed particular focus on reconstructing the onset and tempo of evolution in Badula and assessing the effect of different scenarios of regional geographical configurations on Primulaceae diversification.

The reconstructed chronogram revealed that the Indian Ocean Primulaceae are a monophyletic group, dating back to at least the early to middle Miocene, most likely stemming from long-distance dispersals into the basin through Madagascar, and from there, via a single long-distance dispersal event into the Mascarene Islands. They found evidence for diversification bursts early in the history of Indian Ocean Primulaceae that corresponded closely to the sequence of dispersal and the appearance of newly formed Mascarene Islands. Furthermore, their data indicated that dispersal to Rodrigues might have occurred at a time much older than the current geological age estimate of the island.

The study entitled “Timing and tempo of evolutionary diversification in a biodiversity hotspot: Primulaceae on Indian Ocean islands” has been published in Journal of Biogeography.