Autogamy and Competition for Pollinators in Hepatica americana (Ranunculaceae)

Abstract

Hepatica americana is one of the earliest flowering vernal herbs in the deciduous forests of piedmont North Carolina. Unlike most other members of the spring wildflower community, its flowers are nectarless and autogamous. The number of insect visits a flower receives varies markedly through the blooming season and is lowest when H. americana is in full bloom. Potential for outcrossing as measured by the seed set of emasculated flowers follows the same pattern. The mid-season decline in insect-pollination is most likely the result of competition with Erythronium umbilicatum, which flowers concurrently with H. americana and is much more attractive to the solitary bees that are the principal early season pollen vectors. Because of this competitive disadvantage, seed set of H. americana in piedmont North Carolina would be pollination-limited if the flowers were not autogamous. Autogamy may also be favored by flowering early in the spring before pollinators are available. Opportunities for outcrossing in H. americana are primarily the result of protogyny and blooming earlier than competitors.