Carya illinoensis

The pecan /pɪˈkæn/ (Carya illinoinensis) is a species of hickory native to northern Mexico and the southern United States in the region of the Mississippi River. The tree is cultivated for its seed in the southern United States, primarily in Georgia, and in Mexico which produces nearly half of the world total. The seed is an edible nut used as a snack and in various recipes, such as praline candy and pecan pie. The pecan, in various aspects, is included in state symbols of Alabama, Arkansas, California, Oklahoma and Texas. 'Pecan' is from an Algonquian word variously referring to pecans, walnuts and hickory nuts. There are many variant pronunciations, some regional and others not. The most common American pronunciation is /pɪˈkɑːn/; the most common British one is /pɪˈkæn/. Unusually, there is little agreement in the United States, even regionally, as to the 'correct' pronunciation. The pecan tree is a large deciduous tree, growing to 20–40 m (66–131 ft) in height, rarely to 44 m (144 ft). It typically has a spread of 12–23 m (39–75 ft) with a trunk up to 2 m (6.6 ft) diameter. A 10-year-old sapling grown in optimal conditions will stand about 5 m (16 ft) tall. The leaves are alternate, 30–45 cm (12–18 in) long, and pinnate with 9–17 leaflets, each leaflet 5–12 cm (2.0–4.7 in) long and 2–6 cm (0.79–2.36 in) broad. A pecan, like the fruit of all other members of the hickory genus, is not truly a nut, but is technically a drupe, a fruit with a single stone or pit, surrounded by a husk. The husks are produced from the exocarp tissue of the flower, while the part known as the nut develops from the endocarp and contains the seed. The husk itself is aeneous, that is, brassy greenish-gold in color, oval to oblong in shape, 2.6–6 cm (1.0–2.4 in) long and 1.5–3 cm (0.59–1.18 in) broad. The outer husk is 3–4 mm (0.12–0.16 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. Pecans were one of the most recently domesticated major crops. Although wild pecans were well known among native and colonial Americans as a delicacy, the commercial growing of pecans in the United States did not begin until the 1880s. As of 2014, the United States produced an annual crop of 264.2 million pounds or 132,075 tons, with 75% of the total crop produced in Georgia, New Mexico and Texas. They can be grown from USDA hardiness zones approximately 5 to 9, and grow best where summers are long, hot and humid. The nut harvest for growers is typically around mid-October. Outside the United States, Mexico produces nearly half of the world total, similar in volume to the United States, together accounting for 93% of global production. Generally, two or more trees of different cultivars must be present to pollinate each other. Choosing cultivars can be a complex practice, based on the Alternate Bearing Index (ABI) and their period of pollinating. Commercial growers are most concerned with the ABI, which describes a cultivar's likelihood to bear on alternating years (index of 1.0 signifies highest likelihood of bearing little to nothing every other year). The period of pollination groups all cultivars into two families: those that shed pollen before they can receive pollen (protandrous), and those that shed pollen after becoming receptive to pollen (protogynous). State level resources provide recommended varieties for specific regions. Native pecans in Mexico are adapted from zone 9 to zone 11. Little or no breeding work has been done with these populations. A few selections from native stands have been made such as Frutosa and Norteña which are recommended for cultivation in Mexico. Improved varieties recommended for cultivation in Mexico are USDA developed cultivars. This represents a gap in breeding development given that native pecans can be cultivated at least down to the Yucatan peninsula while the USDA cultivars have chilling hour requirements greater than occur in much of the region. Some regions of the U.S. such as parts of Florida and Puerto Rico are zone 10 or higher, and these regions have limited options for pecan cultivation. 'Western' is the only commonly available variety that can make a crop in low chill zones. Active breeding and selection is carried out by the USDA Agricultural Research Service with growing locations at Brownwood and College Station, Texas. University of Georgia has a breeding program at the Tifton campus working to select pecan varieties adapted to subtropical southeastern U.S. growing conditions.