Biogeographic analyses support an Australian origin for the Indomalesian-Australasian wet forest-adapted tropical tree and shrub genus Alphitonia and its close allies (Rhamnaceae).

The ‘out of Australia’ hypothesis describes taxa with ancestors present on the Australian continent before the contact of the Australian plate with Southeast Asia and the subsequent biological interchange between these regions across Wallacea. Our study supports the ‘out of Australia’ hypothesis for the tropical tree genus Alphitonia and its closest relatives. A common ancestor of the entire clade inhabited Australia in the Miocene, and westward dispersal into Wallacea, the Philippines and the Asian continent was reconstructed to be of Quaternary origin. Furthermore, our study supports the currently applied taxonomy in Alphitonia and related genera, although it highlights potentially underestimated diversity. Finally, our study highlights the need for further investigations in Alphitonia and related genera and for including fossil-rich related taxa. The need for these investigations also arises from a potential human-mediated dispersal of Alphitonia spp. in Polynesia, which cannot be clearly proven by our approach. [ABSTRACT FROM AUTHOR]