Distributed across two continents and thousands of islands, the Asian tropics are among the most species-rich areas on Earth. The origins of this diversity, however, remain poorly understood. Here, we reveal and classify contributions of individual tropical Asian regions to their overall diversity by leveraging species-level phylogenomic data and new fossils from the most species-rich Asian palm lineage, the rattans and relatives (Arecaceae, Calamoideae). Radiators (Borneo) generate and distribute diversity, incubators (Indochina, New Guinea, and Sulawesi) produce diversity in isolation, corridors (Java, Maluku, Sumatra, and the Thai-Malay Peninsula) connect neighboring regions, and accumulators (Australia, India, Palawan, and the Philippines) acquire diversity generated elsewhere. These contrasting contributions can be explained by differences in region size and isolation, elucidating how the unique island-dominated geography of the Asian tropics drives their outstanding biodiversity.