Abstract
Staphylea trifolia L., the bladdernut, is a self‐incompatible temperate woodland shrub that flowers in May in Illinois. Factors limiting reproduction were studied at four levels: 1) Seeds/fruit. Seed production in open‐pollinated fruit was frequently limited by too few fertilized ovules. Seed production in hand‐cross‐pollinated fruit was limited by resources or dispersal constraints: seed abortion rates were higher in hand‐cross‐pollinated fruits than in open‐pollinated fruits. 2) Fruits/flower and 3) fruits/inflorescence. The number of fruits set and matured per flower and per infloresence in the open‐pollinated treatment was limited by the number of flowers naturally cross‐pollinated. In hand‐cross‐pollinated inflorescences, fruit set was not limited by resources even though fruit set was ten times greater than in the open‐pollinated treatment. Evidence that resources limited fruit maturation in the hand‐cross‐pollinated inflorescences was equivocal. In hand‐cross‐pollinated flowers, fruit set was lowest when cold nights followed pollination, suggesting that cool temperatures limited postpollination physiological processes. 4) Fruits/individual. Early‐flowering individuals matured fewer fruits than later‐flowering individuals. Within the latter group, fruit production increased with plant size, although a relatively small individual matured the maximum number of fruits. Flowering phenologies and size of individuals varied among patches, resulting in differential reproductive success of patches.