VARIATION IN FLORAL SEX ALLOCATION WITH TIME OF SEASON AND CURRENCY

Sex allocation patterns and nutrient investments in floral components were investigated in hermaphroditic morphs of Sidalcea oregana ssp. spicata utilizing a micro-technique for the determination of nitrogen and phosphorus content. A plant's investment in flowers and individual floral components decreased from early to late in the season. The primary sexual structures (gynoecium and pollen) showed less severe seasonal declines in nitrogen and phosphorus allocation than did the sepals and petals. Phenotypic gender remained relatively constant throughout the season. Sepals, gynoecium tissue, and pollen had significantly higher concentrations of nitrogen and phosphorus than did the androecium and petals. Pollen had the highest requirement for phosphorus. These results suggest that the sex functions could be limited by different nutrients. Proportional allocation to floral structures varied with time of season and currency used. A seasonal decrease in the proportion of biomass in the sepals was accompanied by an increase in the proportional allocation to each of the reproductive structures. Selection may favor preserving a minimum level of allocation to the primary sexual structures if gamete (or zygote) fitness is influenced by resource availability during production and/or maturation.