Abstract: It has been proposed that relative allocation to female function increases with plant size in animal-pollinated species. Previous investigations in several monoecious Sagittaria species seem to run contrary to the prediction of size-dependent sex allocation (SDS), throwing doubt on the generalization of SDS. Plant size, phenotypic gender, and flower production were measured in experimental populations of an aquatic, insect-pollinated herb Sagittaria trifolia (Alismataceae) under highly different densities. The comparison of ramets produced clonally can reduce confounding effects from genetic and environmental factors. In the high-density population, 48% of ramets were male without female flowers, but in the low-density population all ramets were monoecious. We observed allometric growth in reproductive allocation with ramet size, as evident in biomass of reproductive structures and number of flowers. However, within both populations female and male flower production were isometric with ramet size, in contrast to an allometric growth in femaleness as predicted by SDS. Phenotypic gender was not related to ramet size in either population. The results indicated that large plants may increase both female and male function even in animal-pollinated plants, pointing towards further studies to test the hypothesis of size-dependent sex allocation using different allocation currencies.

Key words: Alismataceae, clonal reproduction, flower production, insect-pollinated, monoecious, Sagittaria trifolia, size-dependent sex allocation.