1. Carya aquatica (F. Michx.) Nutt. (water hickory)

Pl. 430 a–c; Map 1923

Plants trees to 35 m tall (to 45 m elsewhere). Bark light gray to brown, exfoliating from the trunk in long strips or large plates. Twigs 2–3 mm thick, brown to reddish brown or blackish, the terminal bud 8–10 mm long, dark brown, the bud scales meeting at their margins and not or scarcely overlapping, the bractlets around the axillary buds fused into a hood. Leaves with the petiole and rachis pubescent (sometimes becoming nearly glabrous late in the season), with 7–13 leaflets (always 9–13 leaflets in well-developed leaves). Leaflets 2–15 cm long, 1.0–4.5 cm wide, lanceolate to broadly lanceolate, weakly to strongly arched (appearing asymmetrically tapered), the margins entire to wavy or toothed, glabrous, the upper surface glabrous or with scattered hairs along the midvein near its base, sometimes also with scattered, small circular, pale yellow to reddish brown, peltate scales, the undersurface with scattered unbranched and branched (the branches appearing fasciculate) hairs along the midvein and usually also the secondary veins, also with scattered, small, circular, pale yellow to reddish brown, peltate scales. Staminate catkins more or less stalked. Fruits 2–3(–5) cm long, 2–3 cm wide, obovoid, noticeably flattened, with low wings along the 4 sutures, the husk 1–3 mm thick, splitting to the base, with small golden yellow scales that wear off with age. Nut flattened (oval in cross-section), the shell less than 1 mm thick. Seed bitter. April–May.

Uncommon in the Mississippi Lowlands Division (southeastern U.S. west to Missouri and Texas). Swamps, bottomland forests, and margins of oxbows and sloughs.

In Missouri, C. aquatica is known to hybridize occasionally with C. illinoinensis (C. ×lecontei Little).