The pecan (/pɪˈkæn/ pih-KAN, also US: /pɪˈkɑːn, ˈpiːkæn/ pih-KAHN, PEE-kan, UK: /ˈpiːkən/ PEE-kən; Carya illinoinensis) is a species of hickory native to the Southern United States and northern Mexico in the region of the Mississippi River.

The seed is an edible nut used as a snack and in various recipes, such as praline candy and pecan pie.

The outer husk is 3–4 mm (1⁄8–5⁄32 in) thick, starts out green, and turns brown at maturity, at which time it splits off in four sections to release the thin-shelled seed.

Extant examples of Engelhardioideae are generally tropical and evergreen, while those of Juglandioideae are deciduous and found in more temperate zones.

This dispersal strategy coincides with developing a husk around the fruit and a drastic change in the relative concentrations of fatty acids.

In 2017, outside the U.S., Mexico produced nearly half of the world's total, similar in volume to that of the U.S., together accounting for 93% of global production.

[21] Choosing cultivars can be a complex practice, based on the Alternate Bearing Index (ABI) and their period of pollinating.

This represents a gap in breeding development given that native pecans can be cultivated at least down to the Yucatán peninsula while the USDA cultivars have chilling hour requirements greater than those occurring in much of the region.

[29] Active breeding and selection is carried out by the USDA Agricultural Research Service with growing locations at Brownwood and College Station, Texas.

[5] University of Georgia has a breeding program at the Tifton campus working on selecting pecan varieties adapted to subtropical Southeastern U.S. growing conditions.

[3] While selection work has been done since the late 19th century, most acreage of pecans grown today is of older cultivars, such as 'Stuart', 'Schley', 'Elliott', and 'Desirable', with known flaws, but also with known production potential.

[30] The long cycle time for pecan trees plus financial considerations dictate that new varieties go through an extensive vetting process before being widely planted.

Selection programs are ongoing at the state level, with Alabama, Arkansas, Florida, Georgia, Kansas, Missouri, New Mexico, and others having trial plantings.

'Kanza', a northern-adapted release from the USDA breeding program, is a grafted pecan having high productivity and quality, and cold tolerance.

[31] Pecans are subject to various diseases, pests, and physiological disorders that can limit tree growth and fruit production.

These include ambrosia beetles, twig girdlers, pecan nut casebearer, hickory shuckworm, phylloxera, curculio, weevils, and several aphid species.

In the Southeastern U.S., nickel deficiency in C. illinoinensis produces a disorder called "mouse-ear" in trees fertilized with urea.

They can be eaten fresh or roasted, or used in cooking,[33] particularly in sweet desserts, such as pecan pie, a traditional Southern U.S. dish.

Native American tribes would collect the fruit to make flour that was used as a meat substitute and a milky fermented drink called "Pow-cohicora",[39][40][41] along with the bark and leaves made into a tea to heal ailments such as Tuberculosis.

[39]These Spanish explorers called the pecan, nuez de la arruga, which roughly translates to "wrinkle nut".

This was accomplished by an enslaved person called Antoine in 1846 or 1847, who was owned by Jacques Telesphore Roman of the Oak Alley Plantation near the Mississippi River.

[46] The town of San Saba, Texas claims to be "The Pecan Capital of the World" and is the site of the "Mother Tree" (c. 1850) considered to be the source of the state's production through its progeny.