Black walnut is the most valuable tree in Iowa. The leaves are alternately arranged on the twig, compound with 1 to 23 leaflets, and ranging in size from 1 to 2 feet. The terminal leaflet is either absent or much smaller than the leaflets near the middle of the leaf. Twigs are moderately stout to very stout, gray-green or light brown in color and have a chambered pith which is tan to light brown in color. The bark is dark gray or black, deeply furrowed, with interconnecting ridges that become thick and blocky on larger slow growing trees.
Black walnut is native throughout the state.
It occurs on a variety of sites, but is most common on bottomlands, stream terraces, and moist sheltered coves and slopes. It grows best on deep, rich, well drained soils. Common associates of black walnut vary as much as the sites but include oaks, basswood, maples, ashes, and Kentucky coffee tree. Walnut is considered a good invader species and often is one of the first species to become established in abandoned fields and pastures. Squirrels are especially fond of the nuts and aid in the establishment of walnut on these sites.