Lauren Ruane and her students at Christopher Newport University conducted very detailed experiments documenting trait variation and its functional consequences across the geographic range of Clarkia xantiana ssp. parviflora, which is a primarily selfing plant. Floral and mating system variation in selfing taxa is often ignored and assumed not to have important consequences. Our results show considerable variation in the opportunity for outcrossing, the time period during which a plant has the capacity to outcross prior to the deposition of self pollen. In addition to protandry, delayed stigma receptivity differed substantially among some populations, providing a second mechanism for delaying selfing.
Ruane, L., S. Magnum, K.W. Horner, & D.A. Moeller. 2020. The opportunity for outcrossing varies across the geographic range of the primarily selfing Clarkia xantiana ssp. parviflora. American Journal of Botany 107:1198-1207. pdf