4. Carya illinoinensis (Wangenh.) K. Koch (pecan)

Pl. 430 k, l; Map 1926

Plants trees to 35 m tall (to 45 m elsewhere). Bark light gray to brown, smooth or more commonly ridged, sometimes exfoliating from the trunk in small plates. Twigs 3–5 mm thick, tan to reddish brown, the terminal bud 6–10 mm long, yellowish 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 glabrous or sparsely pubescent, with 7–13 leaflets (always 9–13 leaflets in well-developed leaves). Leaflets 2–16 cm long, 1.0–4.5 cm wide, lanceolate to broadly lanceolate, moderately to strongly arched (appearing asymmetrically tapered), the margins finely to coarsely toothed, glabrous or with sparse, evenly scattered hairs, the surfaces rarely with scattered hairs along the midvein near its base, but usually with scattered, minute, gland-tipped hairs and scattered, small circular, pale yellow to reddish brown, peltate scales. Staminate catkins sessile or nearly so. Fruits 3–5 cm long, 1.5–2.5 cm wide, ellipsoid to subcylindrical, not flattened, with low wings along the 4 sutures, the husk 2–3 mm thick, splitting to the base, with small golden yellow scales that wear off with age. Nut not flattened (more or less circular in cross-section), the shell less than 1 mm thick. Seed sweet. 2n=32. April–May.

Scattered nearly throughout the state, but apparently absent from much of the western portion of the Glaciated Plains Division (eastern [mostly southeastern] U.S. west to Iowa and Texas; Mexico; introduced in Arizona, California). Bottomland forests, swamps, banks of streams and rivers, and margins of oxbows and sloughs, also pastures and roadsides.

Pecan is a nut crop of considerable economic importance. Large-scale commercial pecan production is mostly located in the southern states, but the tree is widely cultivated in Missouri.

In Missouri, C illinoinensis is known to hybridize occasionally with C. aquatica (C. ×lecontei Little), C. laciniosa (C. ×nussbaumeri Sarg.), and C. tomentosa (C. ×schneckii Sarg.). Note that Steyermark (1963) and many earlier botanists spelled the species epithet C. illinoensis rather than C. illinoinensis under the mistaken impression that this was a correctable orthographic error in the publication in which the taxon was first described.