Abstract
Dianthus superbus and D. shinanensis are common gynodioecious herbs occurring in grasslands and riverbeds in central Honshu of Japan. We investigated the reproductive nature and pollination systems of the two species to determine what differences in reproductive success and pollination might exist between these taxa and between female and hermaphrodite plants, and whether seed production was limited by pollen availability. In D. superbus the female plants produced more numerous seeds than the hermaphrodite plants, or produced seeds equal to the hermaphrodite ones in natural populations. Both hermaphrodite and female flowers of the species were largely pollinated by large-sized butterflies and hawkmoths sucking the nectars, and did not differ from each other in frequency of flower visitors. In D. shinanensis, on the other hand, the seed set percentages were significantly lower in the female plants than in the hermaphrodite plants. The effective pollinators of the species were mainly middle-sized butterflies sucking the nectars and bees and hover-flies feeding on pollen grains, but the frequency of flower visitors was obviously lower in the female plants than in the hermaphrodite plants. The lower female reproductive success (I. e., seed production) of D. shinanensis may be caused by the reduced visits of the insect pollinators due to lacking pollen rewards.
