Bud-scales valvate, the inner strap-shaped and only occasionally slightly accrescent; fruit more or less broadly winged at the sutures; the thin partitions of the nut containing cavities filled with dark astringent powder (absent in 3 and 5). Shell of the nut thin and brittle; leaflets more or less falcate. Aments of staminate flowers nearly sessile, usually on branches of the previous year; lobes of the seed entire or slightly notched at apex. Leaflets 9—17; nut ovoid-oblong, cylindric; seed sweet. 1. C. pecan (A, C). Leaflets 7—13; nut oblong, compressed; seed bitter. 2. C. texana (C). Aments of staminate flowers pedunculate, on branches of the year or of the previous year; lobes of the bitter seed deeply 2-lobed. Leaflets 7—9; nut cylindric or slightly compressed. 3. C. cordiformis (A, C). Leaflets 7—13; nut compressed, usually conspicuously wrinkled. 4. C. aquatica (C). Shell of the ellipsoidal cylindric nut thick and hard; lobes of the sweet seed deeply 2-lobed; leaflets 7—9, occasionally 5, rarely slightly falcate; aments of staminate flowers long-pedunculate at the base of branches of the year. 5. C. myristicæformis (C). Bud-scales imbricated, the inner becoming much enlarged and often highly colored; aments of staminate flowers on peduncles from the base of branches of the year, rarely from the axils of leaves; fruit usually without wings; partitions of the nut thick without cavities filled with astringent powder; seed sweet, its lobes deeply 2-lobed. Branchlets usually stout (slender in 7); involucre ¼′—½′ in thickness, opening freely to the base. Bark on old trunks separating into long, broad, loosely attached plates; nuts pale. Branchlets light red-brown; shell of the nut thin. Leaflets 5 or rarely 7, obovate to ovate, acute or acuminate; nut much compressed, often long-pointed at apex; branchlets glabrous or pubescent. 6. C. ovata (A, C). Leaflets 5, lanceolate, acuminate; nut little compressed, acute at apex; branchlets slender, glabrous. 7. C. carolinæ-septentrionalis (C). Branchlets pale orange color, pubescent; leaflets usually 7—9; shell of the nut thick. 8. C. laciniosa (A, C). Bark not scaly, on old trunks dark, deeply ridged; leaflets 7—9, often subcoriaceous, pubescent below; nut reddish brown,