Robert H. Mohlenbrock, professor emeritus of plant biology at Southern Illinois University, Carbondale, explores the biological and geological highlights of U.S. national forests and other parklands. Floodplain forest is thick with green ash, American elm, sycamore, cottonwood, and silver maple, with box elder near the water's edge. In early spring, white-flowering bulbous cress and waxy yellow swamp buttercup provide bright splashes on the forest floor. By mid-May, coarse herbs begin to fill the understory, and in summer their junglelike growth can make hiking difficult. A further deterrent is the prevalence of wood nettle and stinging nettle, which have acid-tipped hairs on their stems and leaves.
Mesic forest is dominated by Ohio buckeye, green ash, tulip poplar, and sugar maple.
Here and there is a blue ash, unusual among ashes because of its square twigs. The dense shade of the trees creates a rich habitat for moisture-loving shrubs and wildflowers. Spicebush, with its pleasantly scented leaves, and bladdernut, with its inflated fruits, are the chief shrubs. One bladdernut growing here is certainly among the largest of its kind in the world, having a trunk diameter of six inches. Missouri ironweed, zigzag goldenrod, arrow leaved blue aster, and late boneset provide a second wave of blossoms in autumn.