Sexual Reproduction in Eichhornia crassipes (Water Hyacinth). II. Seed Production in Natural Populations

Abstract

Nineteen populations in 2 tropical regions (Lower Amazon and Costa Rica) and 2 temperate regions (California and southern USA) were surveyed to assess the levels of natural seed production and the occurrence of sexual reproduction in E. crassipes. Of 7750 flowers sampled, 45.9% produced capsules with an average of 44.2 seeds per capsule. Seed production was twice as great in tropical populations as in temperate populations. This difference is probably associated with higher levels of insect visitation to flowers of E. crassipes in tropical regions. Seedlings growing in saturated soil were observed in 3 of the 19 populations. The seasonal pattern of seed production during 1976 was estimated for a population at Stockton, California. Seed production was low at the beginning and end of the fowering season (June-Nov.) but reached a peak in Sept. Controlled field pollinations showed that seed set was sub-maximal throughout the season. The foraging behavior of the honey bee (Apis mellifera) largely determined the seasonal levels of seed production at Stockton. The major factors limiting sexual reproduction in E. crassipes are low and inefficient pollinator service, which limits fecundity, and the absence of suitable ecological conditions for seed germination and seedling establishment.