Resource allocation and floral sex ratios in Zizania aquatica

Abstract

Reproductive effort (RE) in Zizania aquatica (wild rice) averaged about 11% of total biomass except in extremely large plants, in which RE was about 17%. Plant biomass of wild rice was correlated positively with the numbers of male and female flowers produced. The average number of flowers per inflorescence varied markedly among stands and at different times in several lakes in northwestern Minnesota. Floral sex ratios of individuals (and of stands) consistently favored males, but the estimated allocation of biomass to female function (including seeds) consistently exceeded male allocation. Average flora sex ratios of individuals differed among stands and zones within stands, and very often declined steadily on successively produced inflorescences. The observed variation in biomass allocation to each gender and the consistent marked excess of biomass allocation to maternal function do not fit simple expectations of nearly equal expenditures in chiefly outcrossing cosexual plants nor of relatively high male allocation in wind-pollinated plants.