The leaves of aquatic liverwort,Scapania undulata,growing in neutral water contained higher levels of Al, Ca, Fe, and Mn than the leaves of plants from an acidic site. Comparison of the metal concentrations in the leaves and cell walls indicated that Al, Fe, and Mn were localized exclusively in the cell walls. Hematoxylin staining of leaves and the cell wall fraction confirmed the localization of Al in the cell walls. The metal ions were released when the cell wall fraction was incubated in a solution with a pH lower than 4.0, but not when the pH was higher than 5.0. Anionic functional groups in the leaves can act as ligands for metal ions, and competition between these ions and H+may account for the higher metal content of the liverworts from the neutral site.