Medium-length stamen mediates delayed selfing in a two-step self-pollination system in Commelina communis

We examined the functional roles of trimorphic stamens in self-pollination in Commelina communis using quantum dots to label pollen grains. In the absence of pollinators (i.e., under greenhouse conditions), bud pollination and delayed autonomous selfing contributed equally to self-pollination. Delayed autonomous selfing was achieved primarily by the anther of the medium-length stamen (M-anther), whereas the long anthers (L-anthers), positioned adjacent to the stigma during anthesis, and the short anthers (S-anthers), which produce a small number of infertile pollen grains, had no contribution. In field experiments, a low pollinator visit frequency restricted outcross pollination, whereas L-anthers increased their contribution to self-pollination to levels comparable to those of bud pollination and M-anther-mediated selfing. Our results reframe heteranthery in C. communis as part of a temporally structured two-step selfing system and provide a basis for reassessing its functional significance under variable pollination environments.