Mineral concentrations of vegetation in three south Florida marshes were studied. Each marsh was a watershed that had varying degrees of agricultural development: rangeland, tame pasture and one watershed with a combination of rangeland, tame pasture and groveland. Living aerial phytomass was sampled seasonally from summer 1979 through winter 1981 within three distinct communities associated with the freshwater marshes: upland fringe, inundated marsh and the transitional ecotone communities. Samples were analyzed for concentrations of Ca, Fe, K, Mg, Mn, N and P. Except for Fe, mineral concentrations tended to lower in the marsh draining only rangeland—the least agriculturally perturbated. A geneneral trend of increased mineral concentration with increased degree of inundation was measured within the plant communities. Only K concentrations were significantly different among the seasons.