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Tree to 45 m in the wild.Bark pale grey or brownish, ridged or exfoliating in small plate-like scales. Branchlets tan to reddish brown, slender, glabrous or hirsute, scaly. Terminal bud oblong, 0.6–1.2 cm long, yellowish brown. Leaves deciduous, imparipinnate, 30–60 cm long; leaflets (seven to) nine to thirteen (to seventeen), ovate to to lanceolate, often falcate, 2–16 × 1–7 cm, leathery, upper surface glabrous or occasionally pubescent with simple hairs along the midrib, and with scattered 2-6-armed hairs, moderately scaly in spring; lower surface hirsute or with scattered simple and 2-armed hairs, scaly with large peltate scales and small round peltate scales; margins finely to coarsely serrate, glabrous or sparsely pubescent, apex acuminate; lateral petiolules 0–0.7 cm long, terminal petiolules 5–2.5 cm; petiole and rachis glabrous to pubescent; petiole 4–8 cm long. Staminate spikes to 18 cm long, glandular-pubescent. Fruits dark brown, 2.5–6 × 1.5–3 cm, ovoid to ellipsoid, not compressed, splitting to the base or nearly so, sutures winged; nuts finely wrinkled. Stone & Whittemore 1997. Whittemore 2013.
Distribution Mexico Coahuila, Guanajuato, Nuevo León, Oaxaca, Tamaulipas United States Arkansas, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Mississippi, Missouri, Oklahoma, Tennessee, Texas.
USDA Hardiness Zone 5
Bean (1970) gave short shrift to C. illinoinensis on account of it not being well-adapted to the UK climate. He states that having been tried many times at Kew it survives for only a few years, owing to a lack of summer heat to ripen the wood. Nowadays, plants in southern England fare rather better with fine examples at Kew, Windsor and elsewhere. The species is vulnerable to wind damage, however, with a young, vigourous individual growing in the Savill Garden being significantly reduced by high winds in October 2018 (D. Crowley, pers. obvs.). The former UK champion, a tree of 19 m (Johnson 2003) at Cambridge University Botanic Garden was also lost in a storm in 2002 (Kerley et al. 2006). The current champion grows in Poole Park, Dorset (TROBI 2018) and stood at 19 m and although the species can display excellent autumn colour, this specimen has been noted for its lack of colouration (TROBI 2018). The first tree in Europe was speculated by Bean (1970) to be at Padua Botanical Garden, Italy, planted in 1760, which blew down in 1920. In maturity trees forms a huge crown with broadly arching branches.
The tree has long been grown outside of its native range within the United States, to the point at which it has proved difficult to establish the extent of its natural distribution. It is commonly grown as a shade tree and particularly for its sweet, flavourful nuts. Indeed, pecan is one of the most important commercial nut trees in the States with 900 square miles devoted to growing pecan cultivars (Sternberg 2004), of which over 500 have been selected for size, taste and ease of shelling the nuts (Kurz 2003, Sternberg 2004).
Carya illinoinensis can be distinguished from other cultivated species of hickory by its greater number of leaflets, which are distinctly curved. Like other members of the genus it hybridizes readily and crosses with fellow members of section Apocarya, C. aquatica (forming C. × lecontei) and C. cordiformis (forming C. × brownii) as well as with C. laciniosa (forming C. × nussbaumieri), C. ovata and C. tomentosa (forming C. × schneckii) in section Carya. These latter crosses produce the fruits that are known as ‘hicans’, with some grown for their tasty nuts (Sternberg 2004).