Mating system and pollination biology of the spring‐flowering shrub, Dirca palustris

Dirca palustris L., eastern leatherwood or wicopy (Thymelaeaceae), a widely distributed shrub of eastern North America, flowers in early spring and so may face some of the same constraints faced by ephemeral vernal herbs of the eastern deciduous forest, most notably the influence of low temperature on pollinator activity. I studied the mating system of D. palustris and the influence of temperature on pollinator visitation of flowers, during three field seasons in a small stream valley in north‐western Pennsylvania, USA. Specifically, I was interested in how a species with apparently specialized floral morphology, like D. palustris, may ensure reproductive success in a thermally unpredictable vernal environment. Pollinator visitation of flowers of D . palustris was strongly regulated by temperature, with no visits occurring below 14.9°C. Lack of treatment effects in mating system studies, especially the lack of significant differences in fruit set between the bagged, self‐pollination treatment and various cross‐pollination treatments accessible to pollinators, suggests that D. palustris is self‐compatible or perhaps apomictic. Thus, like other spring‐flowering species faced with pollinator unpredictability, D. palustris may rely on a mixed mating system to ensure reproductive success during cool temperate springs.