Lizzie Roeble, Koen van Benthem, Patrick Weigelt, Holger Kreft, Matthew Knope, Jennifer Mandel, Pablo Vargas, Rampal S. Etienne, Luis Valente

The hyperdiverse plant family Asteraceae, with over 32,000 species globally, forms an iconic component of island floras, including many spectacular radiations, but a global picture of their insular diversity is lacking. Here, we uncover the global biogeographical and evolutionary patterns of Asteraceae on islands to reveal the magnitude and potential causes of their evolutionary success. We compile a global checklist of Asteraceae species native and endemic to islands and combine it with macroecological analyses and a phylogenetic review of island radiations. Asteraceae have a global distribution on islands, comprising approximately 6,000 native island species, with 58% endemics. Yet, diversity of the family on islands is lower than expected given its overall diversity. However, Asteraceae are the most diverse family on oceanic islands, suggesting an exceptional ability to thrive in isolation. In agreement with island biogeography predictions, native Asteraceae diversity increases with area and decreases with isolation, and endemism increases with both island area and isolation. The hotspots for insular diversity and endemism are Madagascar and the Caribbean, both being regions we identify as most lacking phylogenetic studies. We identify 39 confirmed island radiations, and 69 putative radiations that remain to be phylogenetically investigated, exceeding numbers for other iconic insular groups, such as birds. Our results reveal Asteraceae offer immense potential for research in ecology and evolution, due to their close tracking of island biogeography expectations, large sample sizes (species and radiations), cosmopolitan distribution, and high number of potentially undiscovered radiations.