As human impacts on island ecosystems increase, so does the importance of understanding life histories of island plants for conservation. Yet, surprisingly little is known about reproductive ecology of many common island plant species. We experimentally investigated the breeding system and observed pollinators of the endemic Hawaiian vine Jacquemontia sandwicensis (Convolvulaceae), a common species in coastal strand habitat. To evaluate the breeding system, experiments involving natural and hand pollination treatments were performed in the field and with cultivated plants. To identify natural pollinators, flower-visiting insects were observed in three sites on the southeastern coast of O‘ahu. Jacquemontia sandwicensis is a self-compatible, hermaphroditic species with a flexible, mixed mating system. High levels of fruit set, seed set, and germinating seeds seem to depend on pollen being deposited on the stigma by an active pollinator rather than a passive vector (wind or autogamy). However, this species still produced some fruit and seeds even in the absence of manipulation, suggesting a limited degree of reproductive assurance when pollinators are absent or in low abundances. At the observed sites, this species was visited by a variety of mostly nonnative Hymenoptera (especially Apis mellifera and Lasioglossum spp.). The endangered native bee Hylaeus anthracinus also visited flowers, but at a much lower rate than the nonnative insects. Nonnative insects appear to be effective pollinators for J. sandwicensis and now play an important role as native pollinators decline.