Hamamelis virginiana flowers late September to late November. In 1977, we began studying the reproductive biology of this eastern USA tree, including: floral phenology and rewards, pollen-ovule ratios, breeding system, pollination, pollinator and resource limitation, and seed dispersal. The homogamous, self-incompatible flowers emit a faint odor, bear nectar with sucrose ratios typical of bee and fly flowers, and produce abundant sticky pollen. Flowers were visited infrequently by insects representing six orders. Flies were the most common floral visitors, specifically members of the genus Bradysia, whereas small bees carried high percentages of Hamamelis pollen. Despite high P/O ratios (11 445 grains/ovule), bees and flies are likely pollinators as experiments indicate wind pollination is much less likely. Pollen quantity and resource availability did not appear to limit reproductive output, but pollen quality did. Tests of > 40 000 flowers showed natural fruit set to be < 1%. The flowering time, breeding system, and clumped dispersion of plants due to limited seed dispersal combine to yield this remarkably low fruit set. Because all other Hamamelis flower from late winter to early summer, it may be that H. virginiana evolved a fall flowering phenology to avoid competition for pollinators with the closely related H. vernalis.

Key words: Breeding System, Floral phenology, Fruit/Flower Ratios, Hamamelis, Pollen-ovule Ratios, Pollination, Pollinator Limitation, Reproductive Limitations