Anther Fusion Enhances Pollen Removal in Campsis grandiflora, a Hermaphroditic Flower with Didynamous Stamens

In many insect‐pollinated angiosperms, stamens are grown with anthers cohered, which might affect pollination processes, but the ecological significance of this fusion of anthers remains unexplored. We studied the breeding system and pollination process of didynamous Campsis grandiflora (Bignoniaceae), with anther fusion in pairs. Pollen removal and deposition were studied in the field for naturally fused versus experimentally separated anthers. Campsis grandiflora flowers were protandrous, with a low pollen:ovule ratio, were mostly outcrossed, and were self‐compatible, with pollinators needed. The main pollinators were pollen‐collecting halictid bees and nectar‐feeding vespid wasps. Halictid bees scooped pollen on long anthers for a significantly longer time period and removed twice as much pollen from fused anthers than from separated anthers. Vespid wasps contacted fused short anthers more frequently and more precisely and removed nearly twice as much pollen than when contacting separated short anthers. Pollen deposition on stigmas was not affected by manipulation of either pair of anthers. Our results suggest that anther fusion can promote pollen removal efficiency by aggregating anthers at a similar position, increasing the pollinator’s contact probability and precision with anthers and extending the visit duration of the pollinator. The maintenance of didynamous stamens may reflect functional advantages of the fused anthers in two distinct heights because they can interact with pollinators of different behaviors and sizes.