Stipe tissues from 18 species of macrofungi collected in the greater Yellowstone National Park-Grand Teton National Park area were analyzed for cation exchange capacity (CEC) and six essential mineral nutrients. Stipe tissue content of the divalent cations, calcium and magnesium, increased significantly with increasing CEC, whereas stipe tissue content of the monovalent cation, potassium, decreased significantly with increasing CEC. These data lend support to the hypothesis that chemical characteristics of fungal cell-walls determine their net ionic charge and the ratio of monovalent/divalent cations that accumulate in apoplasmic space within the wall.