Abstract: To uncover the evolutionary mechanism of floral traits, it’s necessary to analyze the intensity and direction of phenotypic selection. Through manipulating the width of lateral sepals of Aconitum gymnandrum(Ranunculaceae) and phenotypic selection analysis, we examined the relationship between floral traits and fitness of A. gymnandrum. The results showed that, after increasing the width of lateral sepals, the visitation rate of pollinators was significantly decreased, but seed number per flower did not change. Lateral sepals affected pollen export mainly through pollinator attraction rather than seed production. Phenotypic selection estimated through female fitness showed significant linear selection differential on the flower traits except entry width. There was significant linear selection gradient on flower number and plant height, and only flower number was observed with significant nonlinear selection, showing directional selection on plant height and stabilizing selection on flower number. Individuals with taller stature and intermediate flower number would have higher seed production.

Key words: Aconitum gymnandrum, pollinator, lateral sepal, phenotypic selection, female fitness.