Large 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, hairy or not, scaly. Terminal bud oblong, 0.6–1.2 cm long, yellowish-brown. Leaves deciduous, imparipinnate, 30–60 cm long; leaflets (7–)9–13(–17), ovate to lanceolate, often falcate, 2–16 × 1–7 cm, leathery, upper surface glabrous or occasionally pubescent with simple hairs along the midvein, 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. Male catkins to 18 cm, 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 Illinois and south east Iowa south to Texas and Louisiana.
Habitat Stream banks and flood plains, on well-drained soils; 0-600(-1000) m.
USDA Hardiness Zone 5-9
RHS Hardiness Rating H5
Conservation status Least concern (LC)
The Pecan is a valley bottom tree of the Mississippi and its tributaries, although its natural distribution has been blurred by a very long history of human use and cultivation (Grauke 2003). Mature trees may form huge crowns with broadly arching branches. While thriving in moist conditions, it tends to grow on better drained soils, being replaced by C. aquatica on heavy, waterlogged soils (Coladonato 1992). The species was first described by the German botanist and North American tree specialist Friedrich von Wangenheim in 1777 as Juglans illinoinensis. It was transferred to Carya in 1869 by Karl Koch, who sadly mispelled the specific epithet. As a result the name is sometimes printed Carya illinoensis, especially in older literature: this is simply a mistake.
Carya illinoinensis can be distinguished from other cultivated species of hickory by its greater number of leaflets, which are distinctly curved. Its sweet tasting, thin-shelled nuts are not easily confused with other species, but are not freely produced in cool maritime areas such as the United Kingdom.
Of little value as a timber tree, the Pecan is prized for its nuts, which are taken by diverse birds and mammals (Coladonato 1992). It was known to Native Americans, leaves and nuts being found alongside human artifacts in strata dated 6100–3000 BCE in Texas (Grauke 2003). The Commanche ate its nuts and used the pulverised leaves to treat ringworm (Moerman 2019).
Cultivation in North America has always been primarily for nuts, although it makes an effective shade tree. The first plantings were probably in northern Mexico around 1700 by Spanish settlers; early attempts in the north eastern United States began about 70 years later and accelerated through the 19th century. There has been a slow shift from unselected, seed-raised trees to grafted or budded selections, by way of seed-raised cultivars, but material from all levels of domestication contribute to the commercial crop and Wood et al. (1990) were still able to describe the Pecan as ‘relatively undomesticated’. Most American production is in the south. Orchards in the Mesilla Valley of southern New Mexico rely absolutely on irrigation, yet even in the moist climate of Georgia summer irrigation is recommended for optimal yield and nut quality (Tyson 2016). Commercial production in Mexico is second only to the United States, with much smaller crops in South Africa and Australia. The Pecan has long been cultivated in southern and eastern China, alongside the indigenous C. cathayensis. Commercial production is a recent phenomenon in China, but widespread, very extensive young orchards are now starting to yield (Arn et al. 2018).
Bean (1976) speculated that the first specimen in Europe was one planted in 1760 at the Orto Botanico di Padova, Italy; it blew down in 1920. He gave short shrift to C. illinoinensis as a tree for the United Kingdom on account of its being ill adapted to cool summers, citing repeated failures at Kew. 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, vigorous individual growing in the Savill Garden being significantly reduced by high winds in October 2018 (D. Crowley, pers. obs.). 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 (21 m × 62 cm in 2017) and although the species can display excellent autumn colour, this specimen has been noted for its lack of colouration (The Tree Register 2019).
Good specimens are widely reported outside our area in southern Europe, but a tree measured at 21 m in 2019 grows in the Späth Arboretum, Berlin (monumentaltrees.com 2019).
Over 500 cultivars have been selected for size, taste and ease of shelling the nuts (Kurz 2003; Sternberg 2004). They can crudely but usefully divided into northern and southern varieties, the former adapted to colder winters and requiring less summer heat to ripen the wood. While commercial pecan production is largely from southern cultivars, it is the northern varieities – some raised well to the north of the species’ natural range – which are useful in our area. Many cultivars tend to be either protogynous or protandrous, but there is usually a degree of self-fertility (Grauke 2003; Crawford 2016): it makes sense to plant protandrous and protogynous varieties together. We list a few of the most significant and widely available cultivars: all these are sometimes available from European as well as North American nurseries.
One of the ‘ultra-early northern’ cultivars: these are have been selected from the earliest ripening trees in the most northerly populations of the species, and are the only ones viable as far north as southern Ontario (Society of Ontario Nut Growers 2013). Neither strongly protogynous nor protandrous, with small, thick-shelled nuts, and tending to crop biennially. This cultivar orginated in New Boston, Illinois. Other ultra-earlies include ‘Snaps’ and ‘Deerstand’ (Crawford 2016; Grimo Nut Nursery 2019; Reid 2019).
A northern cultivar, hence requiring less summer warmth and tolerating colder winters than the southern varieities. Protogynous, biennial cropping with large, thick-shelled nuts. It tends to produce a strong-structured tree, and the leaves fall late. ‘Colby’ originated as a wild tree near Carlyle, Illinois on the Kaskaskia River flood plain in 1957, selected by A.S. Colby. It is one of the most widely available cultivars (Crawford 2016; Reid 2019).
One of the ‘early northern’ cultivars: these are have been selected from the most northerly populations of the species. Protogynous, producing good, regular crops of medium-sized, well-filled and easily cracked nuts. It originated as a wild tree near Goshen, Ohio. ‘Gibson’ is another early northern cultivar, this time protandrous (Crawford 2016; Reid 2019; De Smallekamp 2019).
A northern cultivar, hence requiring less summer warmth and tolerating colder winters than the southern varieities. Protandrous, a good cropper tending towards being biennial as the tree matures; large, thin shelled nuts with a good flavour. From a British perspective Crawford (2016) notes that it has strong branch angles, while Reid (2019) (working in Kansas) observes that its wood is weak under the stress of an ice storm. ‘Pawnee’ was raised from a controlled cross (‘Mohawk’ × ‘Starking Hardy Giant’) made by the United States Department of Agriculture in 1963; it was named and released in 1984. Today it is one of the more widely available cultivars (Crawford 2016; Reid 2019; De Smallekamp 2019).