Peanut

The peanut or groundnut (Arachis hypogaea) is a species in the pea family Fabaceae native to South America. It is an annual herbaceous plant growing to 30 to 50 cm (one to one and a half feet) tall. The leaves are alternate, pinnate with four leaflets (two opposite pairs; no terminal leaflet), each leaflet 1 to 7 cm (1/3 to 2.75 inches) long and 1 to 3 cm (1/3 to 1 inch) broad. The flowers are a typical peaflower in shape, 2 to 4 cm (3/4 to one and a half inches) across, yellow with reddish veining. After pollination, the fruit develops into a legume 3 to 7 cm (1 to 2 inches) long containing 2 to 3 (rarely 1 or 4) seeds, which forces its way underground to mature. Although a nut in the culinary sense, in the botanical sense the fruit of the peanut is a woody, indehiscent legume or pod.

Cultivation

Evidence demonstrates that the peanut was domesticated in prehistoric times in South America, where wild ancestors are still found. The plant was later spread worldwide by European traders. Cultivation in North America was popularized by African Americans, who brought the Kikongo word goober.

Related Topics:
Domesticated - South America - Europe - African American - Kikongo

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The flower of the Arachis hypogaea is borne above ground and after it withers, the stalk elongates, bends down, and forces the ovary underground. When the seed is mature, the inner lining of the pods (called the seed coat) changes color from white to a reddish brown. The entire plant, including most of the roots, is removed from the soil during harvesting.

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The pods begin in the orange veined, yellow petaled, pealike flowers, which are borne in axillary clusters above ground. Following self-pollination (peanuts are complete inbreeders), the flowers fade. The stalks at the bases of the ovaries, called pegs, elongate rapidly, and turn downward to bury the fruits several inches in the ground to complete their development.

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The pods act in nutrient absorption. The fruits have wrinkled shells that are constricted between the two to three seeds. The mature seeds resemble other legume seeds, such as beans, but they have paper-thin seed coats, as opposed to the usual, hard legume seed coats.

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Peanuts grow best in light, sandy loam soil. They require five months of warm weather, and an annual rainfall of 500 to 1000 mm (20 to 40 in) or the equivalent in irrigation water.

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The pods ripen 120 to 150 days after the seeds are planted. If the crop is harvested too early, the pods will be unripe. If they are harvested late, the pods will snap off at the stalk, and will remain in the soil.

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Poor storage of peanuts can lead to an infection by the mold fungus Aspergillus flavus, releasing the toxic substance aflatoxin.

Related Topics:
Mold - Fungus - Aspergillus flavus - Aflatoxin

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