Relationship between flowering time and fruit set of the entomophilous alpine shrub, Rhododendron aureum (Ericaceae), inhabiting snow patches

Abstract

Flowering phenology, fruit set, and pollinator frequency of the ericaceous alpine dwarf shrub, Rhododendron aureum, were compared among three quadrats arranged along a snowmelt gradient on a slope. Bagging and self‐pollination experiments showed that R. aureum was physiologically self‐compatible, but pollinator visitation highly enhanced fruit set. Depending on the lateness of snowmelt, flowering time varied from mid‐June to late July among quadrats. Pollinator visitation increased as the flowering season progressed, and fruit set was significantly higher in the quadrat with latest snowmelt. Emasculation experiments suggested that later flowering might promote cross‐pollination. Thus, later flowering was advantageous for effective pollination. On the other hand, later‐flowering plants often failed to set fruits because of the onset of autumn frost and snow before fruit maturation.