Premise of the study: Male and female reproductive success is enhanced (increased outcrossing and seed production) by stamen movement in species that have few stamens per flower. Does such enhancement also occur in species that have many stamens per flower?

Methods: We examined the effects of stamen movement on male and female reproductive success in Anemone flaccida, which has many stamens per flower. We measured stamen movement, including temporal changes in anther-stigma and anther-anther distances. We controlled stamen movement experimentally.

Key results: The anthers moved horizontally away from the stigmas with increasing flower age, resulting in reduction in female-male interference. The dehisced anthers tended to move further away from the stigmas while the undehisced or dehiscing anthers remained nearer to them. The number of anthers touched per flower visit was higher in flowers whose stamens were fixed in the pre-movement position than in flowers whose stamens were fixed in the post-movement position or in flowers that were not manipulated. Thus, this position may promote male reproductive success. Seed production was lower for the untreated flowers than for the post-movement position flowers, suggesting that the post-movement stamen position is advantageous and stamen movement is suboptimal for female reproductive success.

Conclusions: Stamen movement promotes male reproductive success in the early flowering stage and female reproductive success in the late flowering stage. In species having many stamens per flower, female-male interference can be reduced, but not eliminated, by stamen movement due to the conflict between female and male reproductive successes.