Plasticity and Timing of Flower Closure in Response to Pollination in Chamerion angustifolium (Onagraceae)

Flower longevity often exhibits a plastic response to pollination and may vary adaptively to maximize pollen removal and deposition and minimize flower maintenance costs. Using Chamerion angustifolium (fireweed), we experimentally tested two predictions that follow from this hypothesis: (1) flower closure should be triggered early, before fertilization, if it is to reduce costs and adjust to maximize pollen receipt; and (2) flower closure should respond differently to different kinds (outcross, self) and amounts (none, low, high) of pollen. In C. angustifolium, flower closure was initiated 4 h after pollination, well before any ovules were fertilized (25 h). The addition of pollen to stigmas significantly shortened the time to closure compared with unpollinated controls. Flower closure times were reduced with increasing pollen loads, up to 700 pollen grains, as might be expected if closure was adaptive. Flower closure was slower in self‐pollinations than outcross pollinations at 24 and 48 h after pollination but not across the whole experiment. These results show that flower closure is highly plastic in fireweed and consistent with an adaptive response in that it promotes seed production and outcrossing over a range of pollination conditions.