Butternut, or white walnut, is a medium-sized tree with a short trunk dividing into several ascending limbs that form an irregular or round-topped crown.
Leaves are alternate, feather-compound, 10–20 inches long, with sticky hairs on the leaf stalk. Leaflets 11–19, 2–4 times longer than broad to lance-shaped, 2–5 inches long, 1½–2 inches wide; margin with small teeth, tip pointed; upper surface yellow-green with fine hairs; lower surface paler, with sticky hairs when young; leaves turn yellow in autumn.
Bark is gray to light brown, sometimes whitish, grooves deep, ridges broad, smooth, flat, short, roughly forming diamond-shaped patterns, chocolate-colored when cut.
Twigs are stout, brown to grayish-brown, hairy; pores white, conspicuous; end bud large, ½–¾ inch long, hairy; pith of twig dark brown, separating into chambers when cut lengthwise.
Flowers April–May. Male flowers in catkins, female flowers in a short spike on the same tree.
Fruits September–October, in clusters of 1–5, drooping, odor strong, 1½–3 inches long, rather cynindrical (broadest in the middle and narrowing at two equal ends), with 2–4 lengthwise ridges, light brown, sticky with rust-brown hairs, not splitting open to expose the nut; nut conspicuously 4-ribbed, sometimes with 4 fainter ribs, light brown, broadest in the middle and narrowing at both ends, 1–2½ inches long; seed sweet, oily, edible.
Similar species: Black walnut (Juglans nigra) is closely related and much more common in Missouri. Its fruits and the nut within are rather spherical; the leaf scars have the upper edge notched (not straight) and are not bordered by a well-definied velvety ridge (as butternut's leaf scars are). The mild-tasting English (or Persian) walnut is the species J. regia. It is native to Eurasia and when cultivated in Missouri does not escape. The state of California grows nearly all of the US commercial supply of English walnuts. Walnuts are in the same family as hickories and pecans.