Ficus (Moraceae) is arguably one of the most important plant genera in lowland tropical rainforests. A brief review of tropical florulas also demonstrates that Ficus is the only ubiquitously diverse genus in lowland rainforests. Monoecious hemiepiphytic figs, constituting independent radiations in each tropical biome, make up a significant proportion of species everywhere, but in Asia dioecious figs have diversified into a variety of niches, making the assemblages of this region especially speciose. Pioneer attributes have endowed figs with tremendous evolutionary flexibility, while long-range seed dispersal ensures that a high proportion of the regional species pool is represented in local assemblages. Large numbers of Ficus species are able to coexist because many are extremely rare as a result of limited recruitment opportunities, which limits competition. They are nevertheless able to breed at low densities because they possess an efficient, long-range pollination system. These factors are likely to be important in the diversity of other plant groups in the tropics.