Dichogamy is very common in flowering plants and is widely thought to reduc
e pollen-pistil interference, especially self-pollination. Yet. the functio
nal significance of dichogamy has rarely been studied. We investigated the
nature and functioning of dichogamy in eastern Ontario populations of Aquil
egia canadensis, a highly selfing columbine previously described as protogy
nous. We then manipulated flowers to determine whether increased protogyny
would reduce self-fertilization. Contrary to previous reports, A. canadensi
s is not dichogamous. Controlled pollinations in a greenhouse showed that p
ollen tubes generally begin to develop after anther dehiscence. Although st
igmas can collect pollen early in floral development, naturally pollinated
flowers collected from four populations had few pollen grains on stigmas an
d almost no pollen tubes in styles until after anther dehiscence. Limited p
ollen deposition before anther dehiscence was also associated with low nect
ar availability and limited sepal expansion. Because inbreeding depression
is strong in this species, selection may favor increased protogyny if it re
duces selfing. We tested this hypothesis by comparing the level of selfing
in flowers rendered protogynous by the removal of the first 19 (of 39) anth
ers to develop, with nonprotogynous control flowers. Contrary to expectatio
ns, protogyny did not reduce selfing. Our results emphasize the importance
of detailed field observations and manipulative experiments in understandin
g the nature and functional significance of dichogamy.