Pollen vectors and inflorescence morphology in four species of Salix

Many plant species exhibit inflorescence morphologies intermediate between pollination syndromes and may therefore employ generalist pollination strategies. We studied how wind and insect pollination are related to inflorescence morphology in the floodplain species Salix alba, S. elaeagnos, S. daphnoides and S. triandra. Insect exclusion experiments showed that all four species were primarily pollinated by insects, but were capable of some seed set when wind was the only pollen vector. Such a generalist pollination system may provide reproductive assurance in these pioneer species. High wind pollination success was associated with slender and divided stigmatic lobes and low ovule number per catkin, which may enhance filtering capacity for airborne pollen. In contrast, species that relied more on insect pollination had robust stigmata and many ovules per catkin, which may reduce the number of insect visits necessary for pollination.