“If You Plant It, Will They Come? Flowering Phenology, Breeding System, and Pollination Ecology of the Threatened Texas Endemic Hibiscus dasycalyx in Natural and Experimental Populations”

I studied the flowering phenology, floral visitors, and breeding system of the threatened Texas endemic Hibiscus dasycalyx in natural (Houston County) and experimental (Walker County) populations during 2024 and 2025. Flowering spanned May to August in the natural population but was largely confined to June in the experimental population. Breeding trials showed the species is self-compatible but not autogamous: fruit set was highest in outcrossed flowers, lower in hand-selfed flowers, and absent in bagged flowers, with no differences in seed set, seed weight or seed germination among self vs crossed treatments. Pollinator activity was abundant in the natural population, producing high fruit set, but much lower in the experimental population, resulting in very low fruit set. Bees and butterflies were the dominant visitors, with the bee Ptilothrix bombiformis accounting for >98% of visits, including pollen collection. Pollen receipt on stigmas also differed significantly between the natural and experimental populations and between periods of high P. bombiformis abundance and absence. These results indicate that pollinator absence constrains reproduction in experimental populations, whereas natural populations benefit from consistent pollination by a specialized bee. However, this opens the potential for hybridization with other co-flowering Hibiscus species.