Polygonum amphibium is a perennial with low sexual reproductive effort and a relatively high degree of flooding tolerance. P. lapathifolium is an annual species with a high sexual reproductive effort and a low tolerance to flooding. P. hydropiperoides is intermediate in terms of sexual reproductive effort and flooding tolerance. P. hydropiperoides and P. amphibium grew best under flooded and partially drained conditions with reduced growth in the drained treatment. P. lapathifolium grew as well in the drained treatment as in the more flooded treatments. Results from competition experiments were consistent in showing the relative competitive abilities to be P. lapathifolium>P. hydropiperoides>P. amphibium, regardless of flooding regime. Thus, short-term competitive performance trades off with flood tolerance rather than with sexual reproductive effort. -from Authors