Horsenettle (Solanum carolinense: Solanaceae) plants possess the ability to bear both hermaphroditic and male flowers on the same plant, a breeding system referred to as andromonoecy. As part of an ongoing investigation into the evolution and maintenance of andromonoecy in horsenettle we conducted a field investigation that addressed the following questions:

We conducted pollen additions on 25 plants in each of two populations, and monitored 25 open pollinated control plants at each site. Mean percentage fruit set and seed set per fruit was significantly greater in the pollen addition treatment than in the control, which indicates that both populations were pollen limited. The percentage of flowers on a plant that were male was significantly greater in the pollen addition treatment than in the control, which suggests that pollen addition affects sex expression in horsenettle. Percentage fruit set did not correlate with total flower number or percentage of male flowers, which indicates that a larger floral display does not affect pollinator behavior in ways that influence female reproductive success. The results document the existence of pollen limitation in the two horsenettle populations studied and suggest that future studies should determine if male flower production influences male fitness or vegetative reproduction.