A large number of flowering plants rely on insects for sexual reproduction: without their pollinators, many angiosperms could go extinct. In southern Florida, the rough-leaf velvetseed, Guettarda scabra L. (Vent.), exists only in remnants of the imperiled pine rockland and hardwood hammock habitats, and depends on insects for its reproduction. This species exhibits all the floral traits typical for attracting nocturnal hawkmoths (Sphingidae), but is also visited by diurnal visitors, since floral reward is available during day time as well. We studied the relative contribution of diurnal and nocturnal pollinators to female reproductive success by selectively exposing the plants to these groups. We also determined the identity of these visitors by direct observation during the blooming period of three consecutive flowering seasons. Plant fruit-set mediated by nocturnal pollinators was significantly higher than by diurnal visitors, although the daytime visitors were apparently more frequent. Our results suggest that even though the flowers of G. scabra are visited by different pollen vectors, nocturnal pollinators are required for successful sexual reproduction in this species, suggesting a rather specialized pollination system.