Floral Biology of Alabama’s Spigelia species (Family Loganiaceae)

Abstract

This thesis examines the pollination ecology of Alabama species of Spigelia. Alabama currently has two species that are under threat of extinction: S. gentianoides and S. alabamensis. The U.S. Fish and Wildlife Service has highlighted the need for studies of the reproductive biology of these species. I analyzed reproductive biology of the rare species S. gentianoides and S. alabamensis, as well as the common species S. marilandica. Determination of likely mating strategies of Spigelia was based on floral morphology and phenology, and evaluation of floral timing. Controlled pollination experiments were used to determine mating system (if flowers are self-compatible or self-incompatible, as well as the degree to which they can outcross). Additionally, floral visitors were observed to identify potential pollinators. Flowers were diurnal, with two-day to three-day longevity, with highly reduced herkogamy and dichogamy to the point where self-pollination is essentially assured. Controlled pollination experiments showed that Spigelia can set fruit via autopollination, selfing, or outcrossing. Floral visitor observations indicated low visitation rates to flowers and few potential pollinators. These results, in addition to prior genetic studies, suggest Spigelia species in Alabama are predominantly selfing. Survival of the remaining populations of the rare species, S. gentianoides and S. alabamensis, is dependent on effective conservation management.