§ 1. Sterile catkins fascicled (no common peduncle or sometimes a very short one) from separate lateral scaly buds near the summit of shoots of the preceding year; bud-scales few; fruit elongated-oblong; the thin-shelled nut 2-celled below; seed sweet; leaflets short-stalked, numerous.
1. C. olivæfórmis, Nutt. (Pecan-nut.) Minutely downy, becoming nearly smooth; leaflets 13–15, oblong-lanceolate, tapering gradually to a slender point, falcate, serrate; nut olive-shaped.—River bottoms, S. Ind., S. Ill., and Iowa, to La. and Tex. A large tree (90–160° high), with delicious nuts.
§ 2. Sterile catkins in threes (rarely more) on a common peduncle from the axil of the inner scales of the common bud, therefore at the base of the shoot of the season, which, then bearing 3 or 4 leaves, is terminated by the fertile flowers; fruit globular or oval; nut 4-celled at base; leaflets sessile or nearly so.
[*] Bud-scales numerous, about 10, successively enwrapping, the inner ones accrescent, becoming thin and membranaceous and rather tardily deciduous; husk of the fruit splitting promptly into 4 more or less thick and when dry hard or woody valves; seed sweet and delicious. (The hickory nuts of the market.)
2. C. álba, Nutt. (Shell-bark or Shag-bark Hickory.) Bark of trunk shaggy, exfoliating in rough strips or plates; inner bud-scales becoming large and conspicuous, persistent till the flowers are fully developed; leaflets 5–7, when young minutely downy beneath, finely serrate, the three upper obovate-lanceolate, the lower pair much smaller and oblong-lanceolate, all taper-pointed; fruit globular or depressed; nut white, flattish-globular, barely mucronate, the shell thinnish.—N. Eng. to N. shore of L. Erie and S. E. Minn., south to Fla., E. Kan., and Tex. Large and handsome tree (70–90° high, or more), of great economic value. The principal hickory-nut of the markets.
3. C. sulcàta, Nutt. (Big Shell-bark. King-nut.) Bark, etc., as in n. 1; leaflets 7–9, more downy beneath; fruit oval or ovate, 4-ribbed above the middle, the husk very thick; nut large (1¼–2´ long) and usually angular, dull white or yellowish, thick-walled, usually strongly pointed at both ends.—Central N. Y. and Penn. to S. Ind., E. Kan., and Ind. Terr. Tree 70–90° high, or more, in rich soil of bottom lands.
4. C. tomentòsa, Nutt. (Mocker-nut. White-heart Hickory.) Bark close, rough, but not shaggy and exfoliating on old trunks; catkins, shoots, and lower surface of the leaves tomentose when young, resinous scented; leaflets 7–9, lance-obovate or the lower oblong-lanceolate, pointed; fruit globular or ovoid, with a very thick and hard husk; nut globular, not compressed, 4-ridged toward the slightly pointed summit, brownish, very thick-shelled, 1´ in diameter or smaller.—N. Eng. to N. shore of L. Erie, E. Neb., and south to the Gulf. Tree 70–100° high, usually on rich upland hillsides.
5. C. microcárpa, Nutt. With rough close bark, small ovate buds, and the glabrous foliage, etc., of n. 6; fruit small, subglobose, with rather thin husk; nut thin-shelled, not angled.—N. Y. to Del., west to Mich. and Ill.
[*][*] Bud-scales numerous or few; husk of the fruit thin and rather friable at maturity, 4-valved only to the middle or tardily to near the base; seed more or less bitter; bark of old trunk not exfoliating.
6. C. porcìna, Nutt. (Pig-nut or Broom H.) Bud-scales nearly as in n. 4, but smaller, caducous; shoots, catkins, and leaves glabrous or nearly so; leaflets 5–7, oblong- or obovate-lanceolate and taper-pointed, serrate; fruit pear-shaped, oblong, or oval; nut oblong or oval (1½–2´ long), with a thick bony shell; the oily seed at first sweet in taste, then bitterish.—S. Maine to Fla., west to Minn., E. Neb., and Tex. Tree 70–90° high (rarely 120°), on dry hills and uplands.