2. Juglans L. (walnut)

Twigs stout, brown to grayish brown, hairy, the pith chambered (hollow between cross-partitions). Leaflets (7–)11–19(–23) per leaf, relatively uniform in size or the median leaflets somewhat larger than the others. Staminate catkins solitary, sessile; each flower with 7–50 stamens. Fruits with the husk relatively thin and fleshy to papery, not splitting, remaining more or less fused with the nut. Nuts deeply grooved or ridged. About 20 species, North America to South America, Europe, Asia.

Two Old World walnut species with edible nuts are sometimes planted in Missouri but do not escape (Steyermark, 1963). The walnut of commerce is J. regia L., called Persian or English Walnut; its leaves have 5–11 broad, entire leaflets. The Japanese walnut, J. ailanthifolia Carrière., has leaves with 9–17 toothed leaflets. Both differ from our native species in having nuts with thinner shells that are wrinkled, not grooved or ridged.

Both of our species provide high-quality lumber and edible nuts, as well as dyes (extracted from the bark and green fruits) that were once important in Missouri.