Heterostyly has been considered rare on oceanic islands. Is heterostyly truly rare on oceanic islands? What makes heterostyly rare on such islands? To answer these questions, we review the reproductive studies of heterostyly on oceanic islands. Overall, not many reproductive studies of heterostyly have been performed on oceanic islands. Shift from heterostyly to other sexual systems may also contribute to rarity of heterostyly, in addition to difficulty of colonization/autochthonous evolution of heterostylous species on oceanic islands. Further investigation of reproductive systems of the heterostylous genus Psychotria on oceanic islands would provide new insights on plant reproduction on oceanic islands.