Novel phylogenomic and biogeographic insights into Palaquium and tribe Isonandreae (Sapotaceae)

Palaquium is currently the largest genus in the sapodilla family Sapotaceae. Previous studies of relationships within Palaquium and its tribe Isonandreae have been based on limited sampling and loci, which have failed to resolve taxonomic boundaries and hindered the understanding of evolution in this Malesian-centric genus. This study uses high-throughput, target capture DNA sequence data to recover phylogenetic relationships in the most comprehensive near species-level sampling to date (∼80 % of 120 recognised Palaquium species as well as representatives of all seven genera in tribe Isonandreae). The analyses confirm that Palaquium is not monophyletic as currently circumscribed. There is a divergent Asian clade more closely related to the genus Isonandra, and the genus Aulandra is nested within Palaquium. The enhanced phylogenetic dataset provided the opportunity to reconstruct biogeographic history, applying both traditional dispersal-extinction-cladogenesis models and a newer modelling framework that accounts for unrecorded extinctions. The results support previous findings of west to east colonisation in the Malesian archipelago, similar to several other plant groups. Recovered diversification timings of Palaquium and tribe Isonandreae are however older than in previous studies, pointing to a boreotropical vicariant signature and ancestral range possibilities within Sundaland that reconcile more closely to Eocene fossil records. These findings enhance our understanding of biogeographic patterns in the biodiversity-rich and geologically dynamic region of Southeast Asia.