Current sex allocation theory assumes that a trade-off exists between allocation to male versus female reproductive effort because a limited pool of resources is available for reproduction. Expected fitness gains derived from investment of resources in each sex differ among pollination mechanisms, mating systems, and plant sizes (including architecture). Platystemon californicus is a self-incompatible, wind-pollinated annual plant exhibiting strict modular growth and extreme variability in numbers of stamens, pollen grains, carpels and ovules within flowers, providing an opportunity to detect results of selection for shifts in phenotypic gender in plants from diverse habitats, of different sizes and at different developmental stages. Number of male and female reproductive structures per flower exhibited significant variation among 41 populations. Comparisons of field versus garden-grown plants from seven populations indicated that numbers of male and female structures were mostly genetically based. Theory predicts that wind-pollinated species should allocate an increased proportion of resources to male function as plants become larger. I found that flowers of larger plants had more stamens, carpels, and ovules and produced more pollen than did flowers of smaller plants. However, the only difference in relative allocation to male vs. female structures was for the ratio of stamens to ovules per flower; larger plants had more stamens per ovule than did smaller plants. Earliest flowers on a plant generally had fewer stamens, carpels and ovules than did later flowers, but relative numbers of flower parts did not differ significantly with developmental stage (although trends toward increasing maleness were found). Although P. californicus is extremely variable in floral construction within and among populations and among plant size categories within populations, the patterns of phenotypic gender modification inferred by current theory were not found.

Key words: Papaveraceae, phenotypic gender, Platystemon californicus, sex allocation theory