There are now recognized[14] fifteen species and several varieties of hickory, all of which grow in the United States east of the Rocky Mountains. Hickory grows in no other place in the world, except one species in northern Mexico. The wood of the different species of hickory is not of equal commercial value, but the wood of the commercial species heads the list of Indiana woods for strength, toughness and resiliency.
The individuals of the several species vary much in respect to their bark, size and pubescence of the twigs, number and size of the leaflets, size and shape of the nuts. No attempt will be made to deal with all of the extreme forms, and only those reported by Heimlich[15] and Sargent[16] will be discussed.
| Bud scales 4-6, valvate (in pairs), leaflets generally curved backward. | |
| Leaflets 9-17, generally about 13; nut elongated, circular in cross-section; kernel sweet | [1 C. illinoensis.] |
| Leaflets 5-9, generally 5-7; nut about as broad as long, compressed in cross-section; kernel bitter | [2 C. cordiformis.] |
| Bud scales more than 6, imbricated (not in pairs); leaflets not curved backward. | |
| Branchlets usually stout; terminal buds large, 7-25 mm. long; the year's growth usually more or less hairy; dry husks 4-10 mm. thick. | |
| Prevailing number of leaflets 5 | [3 C. ovata.] |
| Prevailing number of leaflets more than 5. | |
| Trees of low ground; bark of young trees tight and light, of older trees scaly, separating into long thin plates; branchlets usually light orange color; nuts usually large, compressed, 3-6 cm. long, pointed at base | [4 C. laciniosa.] |
| Trees of high ground; bark of young trees tight and dark, of older trees tight and deeply furrowed, the thick ridges broken into short lengths which on very old trees loosen at the base; branchlets reddish-brown; nuts usually about half as large as the preceding and usually with a rounded base | [5 C. alba.] |
| Branchlets usually slender; terminal buds small, 5-12 mm. long; the year's growth usually glabrous, rarely hairy; dried husk 1-2.5 mm. thick. | |
| Branchlets and leaves not covered when they first appear with rusty-brown pubescence. | |
| Prevailing number of leaflets 5; fruit usually smooth and tapering at base to a short stem (fig-like); shell of nut thick, kernel sweet and astringent | [6 C. glabra.] |
| Prevailing number of leaflets generally 7; fruit usually granular, rarely tapering at the base to a short stem (fig-like); shell of nut thin, kernel sweet without astringency | [7 C. ovalis.] |
| Branchlets and leaves densely covered when they first appear with rusty-brown pubescence | [8 C. Buckleyi.] |
1. Carya illinoénsis (Wangenheim) K. Koch. Pecan. [Plate 22.] Very tall slender trees up to 15 dm. in diameter; bark tight, sometimes becoming scaly on very old trees, fissured, ridges narrow, ashy-brown tinged with red; twigs at first hairy, becoming smooth or nearly so and reddish-brown by the end of the season; leaves 3-5 dm. long; leaflets 9-17, ovate to oblong-lanceolate, somewhat curved backward, 7-15 cm. long, taper-pointed, hairy when they unfold, becoming at maturity smooth or nearly so, dark green above, and a yellow-green beneath; clusters of staminate catkins sessile; fruit single or in small clusters, oblong 3.5-6 cm. long, the winged sutures extending to the base, the husk splitting to below the middle; nut ovoid-oblong, reddish-brown; wood heavy, hard and not strong.
Distribution.—In the Mississippi Valley from Indiana and Iowa south to Texas. In Indiana it was a native of the southwest part of the State. It was a common tree in the river bottoms of Point Township of Posey County, and in the bottoms of the southwest part of Gibson County. It was found more or less frequently in the bottoms of the Wabash Valley, as far north as to within four miles of Covington where the author collected specimens in 1918. It followed the bottoms of the Ohio River east at least as far as Clark County. Michaux[17] gives it as rare in the vicinity of Louisville. Victor Lyons of Jeffersonville says that it was a native to the east part of Survey 29 of the Illinois Grant, and one tree in the northwest corner of No. 32; and there were nine trees 9-10 dm. in diameter in Floyd County on "Loop Island". A large tree grew in the bottoms near Bethlehem in Clark County, which is said to have been a native.
Young[18] says that there are two trees in Jefferson County, one planted, the other probably native. Coulter[19] says "there are several trees in the river bottoms."
