Evolutionary time and climatic stability as underlying drivers for floristic hyperdiversity across global biodiversity hotspots

math_shortcuts Biodiversity hotspots contain high species richness and endemism, but whether shared eco-evolutionary dynamics underlie this diversity remains unknown. We synthesized species richness, diversification rate, and age for 1,928 plant lineages across 21 hotspots, and applied phylogenetic comparative methods to disentangle shared and idiosyncratic drivers of diversity across hotspots. Hotspots differed substantially in their evolutionary dynamics: the highest diversification rates were found in island-like hotspots (Páramo and the Hawaiian Islands), and the oldest lineages in Southeast Asia and the Himalayan-Hengduan hotspots. Furthermore, older lineages had more species, and lineages that evolved in hotspots that have been climatically stable over time had higher diversity and diversification rates. Regions that shared a common environment (e.g., Mediterranean climate) were often similar in lineage ages and diversification rates, suggesting shared ecological opportunities. Our results indicate that the most diverse biodiversity hotspots contain old lineages that have accumulated diversity over time, but the highest diversification rates are found in young, island-like hotspots. Furthermore, lineages within biodiversity hotspots share similar ages and rates, suggesting that region-specific drivers have shaped lineages in similar ways. Our synthesis sets the stage for further investigation on whether hotspot lineages also respond in concert to ongoing threats of extinction.