Generalized pollination of morphologically specialized Vincetoxicum hirundinaria (Apocynaceae, Asclepiadoideae)

Generalized pollination systems with ecologically and/or functionally diverse pollinator assemblages are common in nature. However, the extent to which a plant with specialized floral morphology can exhibit a generalized pollination system remains poorly understood. We investigated this question using Vincetoxicum hirundinaria Medik. (Apocynaceae, Asclepiadoideae) as a model system-a species whose morphologically specialized flowers are described as being visited by flies, bees, and moths. In preliminary observations, we even found various other insects as flower visitors. We hypothesized that V. hirundinaria has a more diverse pollinator spectrum than previously known. To test this hypothesis, we studied the flower biology and pollination ecology of V. hirundinaria at several sites in and around Salzburg. Our findings reveal that the self-incompatible, pale white to ivory-coloured flowers open between 4 p.m. and 6 p.m., and attract a diverse community of both diurnal and nocturnal pollinators, including cockroaches, beetles, and ants not previously reported as pollinators of V. hirundinaria. Pollen transfer efficiency and fruit set were low. A high number of non-pollinator species got trapped by the flowers, often fatally. Overall, V. hirundinaria has a more generalized pollination system than previously recognized, showing that a complex floral morphology can coexist with ecological and functional generalization.