The reproductive biology of Vaccinium cylindraceum Smith, an endemic species confined to the islands of the Azores archipelago, was studied in populations from seven islands. Data indicate that the breeding system of the species is facultative xenogamy with spontaneous autogamy playing a minor role in fruit development. Stigma–anther distance was correlated with style length. Species of microlepidoptera were the most frequent floral visitors, and are possibly important pollinator taxa. Variation in flower, fruit, and seed morphology, as well as seed germination was significant among populations from the islands. The time each island has been available for colonization–evolution, as well as bird-assisted colonization of the Azores archipelago through transport of seeds from the South, likely play a role in floral and other characteristics of V. cylindraceum populations. The central group of islands is the centre of maximum differentiation of populations.