2. Juglans nigra L. (black walnut, eastern black walnut)

Pl. 431 l–n; Map 1933

Plants trees to 35 m tall (to 50 m elsewhere). Bark medium to dark gray or brown, deeply split into narrow, rough ridges. Pith light brown. Terminal buds 8–10 mm long, ovoid or subglobose, weakly flattened. Leaf scars with the upper margin notched, glabrous or sometimes velvety, but never forming a prominent velvety ridge. Leaves 20–60 cm long, the petiole 6.5–14.0 cm long, glandular-hairy, with (9–)15–19(–23) leaflets, sometimes including a small terminal leaflet. Leaflets (3–)6–15 cm long, 1.5–5.5 cm wide, lanceolate to narrowly ovate, more or less symmetrical or slightly arched (appearing slightly asymmetrically tapered), rounded to shallowly cordate (sometimes asymmetrically so) at the base, tapered at the tip, the margins finely toothed, yellowish green to green, the upper surface with scattered gland-tipped hairs and fasciculate hairs only along the midvein, the undersurface with moderate to abundant unbranched or 2-branched hairs (the branches appearing fasciculate) on and between the veins. Staminate catkins 5–10 cm long, the staminate flowers with 17–50 stamens, the anthers 0.8–0.9 mm long. Fruits usually solitary or paired, 4–8 cm long, subglobose to globose or rarely ellipsoid, the husk somewhat warty to nearly smooth, with scattered gland-tipped hairs and dense, minute scales, remaining fleshy or becoming somewhat leathery with age. Nuts 3–4 cm long, subglobose to globose or rarely ellipsoid, with numerous, irregular, rounded, longitudinal grooves and coarsely warty between the grooves. 2n=32. April–May.

Scattered to common nearly throughout the state (eastern U.S. west to North Dakota and Texas; Canada; introduced farther west). Bottomland forests, mesic upland forests, bases of bluffs, and banks of streams and rivers; also margins of pastures and crop fields, railroads, and roadsides.

Black walnut is one of the premier hardwood timbers of North America. The nuts are a minor trade item; they surely would be used heavily if it were not so difficult to extract the nutmeat from the thick shell. In 1990, the Missouri legislature officially designated the eastern black walnut as the state nut, although at least one senator was of the opinion that this measure proved that Missouri had 197 state nuts sometimes also known as legislators (V. Young, 1990). The process of shelling the nuts (removing the husks) produces a strong unpleasant odor and stains the hands.

Walnut trees frequently have few plants growing close-by. A quinone compound known as juglone is produced mainly by the roots and fruit husks and has a strong allelopathic effect, inhibiting the establishment and growth of many other plant species (for a review, see Rice, 1984).

Plants with ellipsoidal fruits have been called f. oblonga (Marsh.) Fernald.