Pollination of Nuphar (Nymphaeaceae) in Europe: flies and bees rather than Donacia beetles

Nuphar (Nymphaeaceae) comprises a small holarctic group of aquatic perennials whose flowers are pollinated by flies, bees, and beetles. We studied pollination in different populations of the two European species N. lutea and N. pumila in Norway and in Germany. Flowers are self-compatible and protogynous, preventing automatic selfing, and insect pollination is required for seed production. Sympatric populations were studied in Vest-Agder county in Norway to determine whether N. lutea and N. pumila have the same or different pollinators. Allopatric populations of N. lutea in Germany and Norway were then compared to determine whether their pollinator spectra differ as would be expected in an open flower with seemingly easily accessible pollen and nectar. Results of the present as well as previous studies of the pollination of N. lutea and N. pumila show that both species are mainly pollinated by flies, including apparent Nuphar specialists, such as the scatophagid Hydromyza livens and the ephydrids Hydrellia and Notiphila, the last also a long-known pollinator of N. advena in Florida. Pollinator overlap between sympatric heterospecific populations was small, while allopatric conspecific populations had similar visitor and pollinator spectra. We found no evidence of pollination by Donacia beetles as reported from some North American populations of Nuphar.