The black walnut tree is native to the eastern United States. A mature black walnut can stand up to 75 feet tall and reach a spread of 60 feet. People have long cultivated black walnut trees for their rich-tasting nuts and for hardwood. To identify a black walnut tree, look at the leaves, nuts and bark.
Look at the leaves of the tree. A black walnut tree is a deciduous broadleaf---its leaves are flat and thin, and they fall off in the winter.
Look at the stalk that attaches the leaves to the tree. A black walnut has compound leaves---several leaves grow out of a single stalk, as opposed to each leaf attaching directly to the tree by its own stalk.
Look at how the compound leaves alternate on the stalk. A black walnut tree's compound leaves aren't exactly opposite one another on the stalk. Arborists call this a "compound alternate" arrangement of leaves.
Now, look at the leaves themselves. The edges leaves of the black walnut have small indentations, not deep ones.
Look at the compound leaf stems, with their accompanying leaves, to see how they attach to the tree. Each compound leaf of the black walnut grows directly out of the tree---in other words, several compound leaves connect to one another by yet another stem, which then grows out of the tree.
Look to see how new buds are emerging on the tree. On a black walnut tree, the buds are visible, as opposed to being hidden by the bases of the leaves.
Pick a leaf, crush it in your hand, and then take a sniff. Black walnut trees don't have an unpleasant, musty odor.
Find an old nut---there are probably several lying on the ground close to the tree. Black walnut fruits are round, and when they ripen, the husks split irregularly, not in clean lines.
Look at the tree's bark. If it's a black walnut, the bark will be dark brown or nearly black.