This study analyzed macrophyte richness, biomass, and composition under flooding of brief duration (less than 3 days) and drawdown events over an annual cycle in a floodplain palustrine wetland in the south of Brazil. The study was carried out to test the hypothesis that floods of brief and very brief duration are not long enough to compromise the richness and the biomass of aquatic macrophytes and that the alternation between wet and drawdown phases may cause variations in the macrophyte richness and composition. A total of 26 aquatic macrophyte species were observed from April 2003 to May 2004: 13 species were observed during the wet phase, and 24 during the drawdown phase. The mean richness was higher during the drawdown phase than during the wet phase, however, the mean biomass was similar in both phases. Although macrophyte richness was not modified after the three flooding events, mean biomass was modified after two events. The number of macrophyte species of which the biomass was modified after the first flooding event increased with subsequent floods. These results illustrate the importance of the dynamics between brief floods and drawdown events to the aquatic plant community in floodplain wetlands in southern Brazil.