Summary
Studies were made on the reproductive biology and growth of Pistia stratiotes L. on plants growing in varzea lakes (of the Janauaca lake system and in the rio Solimões). Some observations were also made on herbivore predation of the species. The results indicate that young plants invest more energy In leaf production while adult plants invest more energy in stolon production. Abiotic factores (dry period) seem to be more important in the control of the plant populations than herbivores. Sexual reproduction seems to be entering a degenerative stage. During the low-water period the populations of the study areas are dying out; germination of seeds does not seem to play an important role in the build-up of the populations in the area during rising water, rather it is the result of vegetative reproduction of isolated surviving plants.