Does sexual dimorphism exist in flowering phenology traits in anemophilous dioecious species? A test with Rumex acetosa.

Premise: Sexual dimorphism in flowering phenology traits may have evolved under sexual selection and vector‐mediated selection. The conspicuous sexual dimorphism and sex‐specific selection pressures in flowering phenology traits have been investigated mainly in entomophilous dioecious plants, whereas little is known about this in anemophilous plants. Methods: We examined sexual dimorphism in flowering onset, flowering peak, flowering duration, maximum proportion of open flowers per inflorescence branch, maximum proportion of newly opening flowers on a given date per branch, and longevity of individual flowers in natural Rumex acetosa populations. Correlations between flowering phenology traits and the degree of flowering overlap with the opposite sex were examined. We also tested whether the overlap of female flowering with male flowering enhanced seed set in female plants. Results: Little sexual dimorphism was observed in flowering onset, peak, duration, and maximum proportion of newly opening flowers. Females had greater floral longevity and greater maximum proportion of open flowers than males. Flowering overlap with the opposite sex significantly increased with the maximum proportion of newly opening flowers and decreased with temporal deviation in the flowering peak in both sexes. Females with greater flowering overlap with males set more seeds in two of the three study populations. Conclusions: In wind‐pollinated R. acetosa, little sexual dimorphism in phenological traits may have evolved to achieve synchronous flowering with the opposite sex. Our results suggest that, in angiosperms, not only common selection but also anemophily‐specific selection may shape little sexual dimorphism in R. acetosa, unlike in entomophilous plants. [ABSTRACT FROM AUTHOR]