The chambered pith is a good character to help distinguish this genus in our area, and the leaf scar lacking a band of hairs above the top edge will help to distinguish Black Walnut from the similar Butternut (Juglans cinerea). The fruit of Black Walnut is roughly spherical, compared to the fruit of Butternut which is clearly longer than wide. Butternut leaves are often densely hairy beneath with stellate hairs (branched hairs). Black walnut leaves are much less hairy and the hairs are simple (not branched).

Juglans nigra is apparently native in about the 3 southernmost rows of counties in Wisconsin. Most or all of the scattered sites reported farther north are probably planted trees or escapes from nearby planted trees, as has been observed in Green Bay. Habitat for naturally occurring plants includes both wet and dry sites, and they do not tolerate heavy shade.