Activity of root phosphatase was examined in Cladium jamaicense (sawgrass) and Typha domingensis (cattail) grown under controlled conditions in Everglades peat with different inorganic P availabilities and flooding regimes. Cladium root phosphatase activity was significantly greater than for Typha when both were subjected to relatively low inorganic phosphorus concentrations (10 to 80 μg l⁻¹) in the interstitial water, indicating a greater potential for Cladium to use organic phosphorus compounds as a phosphate source. When inorganic phosphorus concentration was elevated (500 μg l⁻¹), internal root phosphate concentrations increased and root phosphatase activities decreased in both species to similar levels. Thus, root phosphatase activity in these species is induced by low ambient inorganic phosphate concentrations. The relatively greater ability of Cladium to hydrolyze organic phosphorus compounds indicates that it is physiologically better adapted to peat-based, low inorganic phosphorus conditions and helps explain this species' historic dominance in peat-based Everglades soils.