Plant community composition on small and remote, oceanic islands is expected to be governed by extremely low immigration, and high extinction, rates. In such communities, resident species are more likely to display reproductive features that mediated their establishment and short-term survival than to have evolved alternatives that ensure long-term persistence. In this extreme version of Baker’s law, small, remote island communities are always young and are dominated by species that arrived with highly evolved selfing syndromes. Alternatively, biological changes that increase selfing success might have evolved from more outcrossing mainland progenitors after arrival. In this study, we sought to determine the degree to which island species have diverged from their mainland conspecific or nearest-relative counterparts in their breeding and sexual systems. We performed hand-pollinations on 36 native flowering species on Pohnpei, Federated States of Micronesia to characterize sexual systems and to quanitify the degree of compatibility, autonomous self-fertilization, and pollen limitation. We used phylogenetic generalized least squares analyses to compare these data with studies of their nearest phylogenetic relatives from continental mainlands, all of whom are typically animal-pollinated. All 36 Pohnpei island taxa were hermaphroditic and self-compatible with bisexual flowers and incomplete dichogamy. The mainland counterpart taxa had either bisexual or rarely some combination of bi- and/or uni-sexual flowers, on the same plant, and all but three were self-compatible. On Pohnpei, all but two species had high autofertility indices (AFI > 0.4), and in these, self-pollination (autonomously and/or by hand) produced higher seed sets than either outcross or open, emasculated pollinations. Among 32 mainland-island pairs, Pohnpei island taxa had a 27% higher mean self-compatibility index (SCI, based on fruit set; P = 0.0015) and a 42% higher mean AFI (based on seed set; P