Format: ORAL

Pirada Sumanon1,2, Timothy M.A. Utteridge3,4, Henrik Balslev2 Wolf L. Eiserhardt2,3

1 Silpakorn University, Sanam Chandra Palace campus, Nakhon Pathom, Thailand 2 Aarhus University, Aarhus, Denmark 3 Royal Botanic Gardens, Kew, United Kingdom 4 Singapore Botanic Gardens, Singapore

The Indo-Australian Archipelago is recognized as one of the worlds most geologically and biogeographically complex areas with exceptional floristic diversity. These islands are situated between mainland Southeast Asia and Australia, acting as an area of floristic interchange. However, the pathways of plant dispersal across the region are still unclear. Although west-to-east dispersal into the Pacific is detected in several plant groups, the generality of this pattern remains to be tested. Maesa is a genus of shrubs, trees, or woody scramblers in the family Primulaceae distributed in the palaeotropics from Africa to the Pacific comprising approximately 200 species. In this study, we reconstructed dispersal events of Maesa focusing on the Indo-Australian Archipelago and the connection to continental Asia and the Pacific islands. We used a comprehensive species-level phylogeny generated from genomic (target sequence capture) data for molecular dating and ancestral range estimation. The phylogeny showed several strongly supported clades, including three geographically structured Asian-Pacific clades. The Asian-Pacific lineage diverged from its African relatives ca. 15 Ma and established in Continental Asia-Papuasia-Philippines ca. 11 Ma. However, the recent diversity of the genus in the Asia-Pacific is a result of rapid radiations that happened ca. 5 Ma possibly related to a warming phase and rapid orogenesis. Papuasia and Continental Asia are inferred as major sources of Maesa. We detected two west-to-east dispersal trends: from continental Asia to west Malesia and from Papuasia to Pacific Islands. No connecting path is recovered which might be due to incomplete sampling especially from the Philippines. This study is the first to explore historical biogeography of the genus Maesa. Our investigation into the biogeographic history of the genus reveals the events that shape the current distribution of Maesa and shed light on the connectivity between the complex Indo-Australian Archipelago and neighbouring islands and continents.