_Carya_ is confined to the temperate region of eastern North America from the valley of the St. Lawrence River to the highlands of Mexico, and to southern China where one species occurs. Of the seventeen species, fifteen inhabit the territory of the United States.
The generic name is from Καρύα, an ancient name of the Walnut.
CONSPECTUS OF THE SPECIES OF THE UNITED STATES.
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, often long-pointed, thick shelled; branchlets pubescent. 9. C. alba (A, C). Branchlets slender; leaves 5—7-foliolate; involucre of the fruit tardily dehiscent to the middle, indehiscent or opening freely to the base; shell of the nut thick, bark close, (sometimes scaly in 13). Branchlets and leaves not covered when they first appear with rusty brown pubescence. Involucre of the fruit 3—5.5 mm. in thickness, opening freely to the base, leaves usually 7-foliolate; winter-buds pubescent. Leaflets hoary tomentose below in early spring, slightly pubescent at maturity; petioles and rachis glabrous; fruit broad-obovoid; branchlets glabrous. 10. C. leiodermis (C). Leaflets covered in early spring with silvery scales, pale and pubescent below during the season; petioles and rachis more or less thickly covered with fascicled hairs; fruit ellipsoidal to obovoid or globose; branchlets glabrous or slightly pubescent. 11. C. pallida (A, C). Involucre of the fruit 1—3 mm. in thickness; winter-buds glabrous or puberulous. Leaves 5, rarely 7-foliolate, glabrous or rarely slightly pubescent; fruit obovoid, often narrowed below into a stipitate base, the involucre indehiscent or tardily dehiscent. 12. C. glabra (A, C). Leaves generally 7-foliolate, glabrous or rarely pubescent; fruit ellipsoidal, subglobose or obovoid, the involucre opening freely to the base; bark often more or less scaly. 13. C. ovalis (A, C). Branchlets and leaves densely covered when they first appear with rusty brown pubescence; leaflets usually 5—7; winter-buds rusty pubescent. Fruit obovoid; the involucre 2—3 mm. in thickness; peduncles of the aments of staminate flowers often from the axils of leaves; branchlets soon becoming glabrous. 14. C. floridana (C). Fruit subglobose to broadly obovoid, ellipsoidal or pyriform, the involucre on the different varieties 2—13 mm. in thickness; branchlets pubescent through their first season. 15. C. Buckleyi (A, C).