The peanut (Arachis hypogaea), also known as the groundnut,. goober (US, via Kikongo), goober pea, pindar (US, via Kikongo) or monkey nut (UK), is a legume crop grown mainly for its edible seeds, contained in underground pods. It is widely grown in the tropics and subtropics by small and large commercial producers, both as a grain legume and as an oil crop. Underground fruiting (geocarpy) is atypical among legumes, which led botanist Carl Linnaeus to name the species hypogaea, from Greek 'under the earth'.
The peanut belongs to the flowering plant family Fabaceae (or Leguminosae), commonly known as the pea family, and is native to South America. Like most other legumes, peanuts harbor symbiotic nitrogen-fixing bacteria in root nodules, which improve soil fertility, making them valuable in crop rotations.
Edible products include peanut oil and peanut butter. Peanut sauces are used in Latin America, West Africa, and Southeast Asia, while in the Indian subcontinent, they are added to salads and stews. In North America, peanuts are used in candies, cakes, and cookies, while peanut butter is widely eaten. Some people are allergic to peanuts and can have a fatal reaction.
The plant tops are used for silage, while oilcake meal is used as animal feed and as a fertilizer. Industrial uses include paint, varnish, and furniture polish made with peanut oil.
Botanical description
Arachis hypogaea was described by Carl Linnaeus in his Species Plantarum in 1753. It is an annual herbaceous plant growing tall. It belongs to the botanical family Fabaceae, also known as Leguminosae, and commonly known as the legume, bean, or pea family. Like other legumes, peanuts harbor symbiotic nitrogen-fixing bacteria in their root nodules.
The leaves are opposite and pinnate with four leaflets (two opposite pairs; no terminal leaflet); each leaflet is long and across. Like those of many other legumes, the leaves are nyctinastic; that is, they have "sleep" movements, closing at night. The flowers are across, and yellowish orange with reddish veining. They are borne in axillary clusters on the stems.
Peanut fruits develop underground, an unusual feature known as geocarpy. After fertilization, a short stalk at the base of the ovary—often termed a gynophore, but which appears to be part of the ovary—elongates to form a thread-like structure known as a "peg". This peg grows into the soil, allowing the fruit to develop underground. These pods, technically called legumes, are long, normally containing one to four seeds. The shell of the peanut fruit consists primarily of a mesocarp with several large veins traversing its length. Botanically they are not nuts ("fruit whose ovary wall becomes hard at maturity").
Peanuts contain polyphenols, polyunsaturated and monounsaturated fats, phytosterols, and dietary fiber in amounts similar to several tree nuts. Peanut skins contain resveratrol.
History
The Arachis genus is native to South America, east of the Andes, around Peru, Bolivia, Argentina, and Brazil. Cultivated peanuts (A. hypogaea) arose from a hybrid between two wild species of peanut, thought to be A. duranensis and A. ipaensis. The initial hybrid would have been sterile, but spontaneous chromosome doubling restored its fertility, forming what is termed an amphidiploid or allotetraploid. Genetic analysis suggests the hybridization may have occurred only once and gave rise to A. monticola, a wild form of peanut that occurs in a few limited locations in northwestern Argentina, or in southeastern Bolivia, where the peanut landraces with the most wild-like features are grown today, and by artificial selection to A. hypogaea.
The process of domestication through artificial selection made A. hypogaea dramatically different from its wild relatives. The domesticated plants are bushier, more compact, and have a different pod structure and larger seeds. From this center of origin, cultivation spread and formed secondary and tertiary centers of diversity in Peru, Ecuador, Brazil, Paraguay, and Uruguay. Over time, thousands of peanut landraces evolved; these are classified into six botanical varieties and two subspecies (as listed in the peanut scientific classification table). Subspecies A. h. fastigiata types are more upright in their growth habit and have shorter crop cycles. Subspecies A. h. hypogaea types spread more on the ground and have longer crop cycles.
The oldest known archeological remains of pods have been dated at about 7,600 years old, possibly a wild species that was in cultivation, or A. hypogaea in the early phase of domestication. They were found in Peru, where dry climatic conditions are favorable for the preservation of organic material. Almost certainly, peanut cultivation predated this at the center of origin where the climate is moister. Many pre-Columbian cultures, such as the Moche, depicted peanuts in their art.Berrin, Katherine & Larco Museum. The Spirit of Ancient Peru: Treasures from the Museo Arqueológico Rafael Larco Herrera. New York: Thames & Hudson, 1997. Cultivation was well-established in Mesoamerica before the Spanish arrived. There, the conquistadors found the (the plant's Nahuatl name, hence the name in Spanish cacahuate) offered for sale in the marketplace of Tenochtitlan. Its cultivation was introduced in Europe in the 19th century through Spain, particularly Valencia, where it is still produced, albeit marginally. European traders later spread the peanut worldwide, and cultivation is now widespread in tropical and subtropical regions. In West Africa, it substantially replaced a crop plant from the same family, the Bambara groundnut, whose seed pods also develop underground.
Peanuts were introduced to the U.S. during the colonial period and grown as a garden crop. Starting in 1870, they were used as an animal feedstock until human consumption grew in the 1930s.Putnam, D.H., et al. (1991) Peanut . University of Wisconsin-Extension Cooperative Extension: Alternative Field Crops Manual. George Washington Carver (1864–1943) championed the peanut as part of his efforts for agricultural extension in the American South, where soils were depleted after repeated plantings of cotton. He invented and promulgated hundreds of peanut-based products, including cosmetics, paints, plastics, gasoline and nitroglycerin.
Peanut butter was first manufactured in Canada by a process patented in the U.S. in 1884 by Marcellus Gilmore Edson of Montreal. Peanuts were sold in North America at fairs or by pushcart operators throughout the 19th century. Peanut butter became well known in the United States after the Beech-Nut company began selling it at the St. Louis World's Fair in 1904. The U.S. Department of Agriculture initiated a program to encourage agricultural production and human consumption of peanuts in the late 19th and early 20th centuries.
Cultivation
Agronomy
Peanuts grow best in light, sandy loam soil with a pH of 5.9–7. Their capacity to fix nitrogen means that providing they nodulate properly, peanuts benefit little or not at all from nitrogen-containing fertilizer,Baughman, Todd; Grichar, James; Black, Mark; Woodward, Jason; Porter, Pat; New, Leon; Baumann, Paul; McFarland, Mark "Texas Peanut Production Guide " (PDF). Texas A&M University. Retrieved October 16, 2015, and they improve soil fertility. Therefore, they are valuable in crop rotations. Also, the yield of the peanut crop itself is increased in rotations through reduced diseases, pests, and weeds. For example, in Texas, peanuts in a three-year rotation with corn yield 50% more than non-rotated peanuts. Adequate levels of phosphorus, potassium, calcium, magnesium, and micronutrients are also necessary for good yields. Peanuts need warm weather throughout the growing season to develop well. They can be grown with as little as of water, but for best yields need at least . Depending on growing conditions and the cultivar of peanut, harvest is usually 90 to 130 days after planting for subspecies A. h. fastigiata types, and 120 to 150 days after planting for subspecies A. h. hypogaea types.
Peanut plants continue to produce flowers when pods are developing; therefore, some pods are immature even when they are ready for harvest. To maximize yield, the timing of harvest is important. If it is too early, too many pods will be unripe; if too late, the pods will snap off at the stalk and remain in the soil. For harvesting, the entire plant, including most of the roots, is removed from the soil.
The main yield-limiting factors in semi-arid regions are drought and high-temperature stress. The stages of reproductive development before flowering, at flowering, and at early pod development are particularly sensitive to these constraints. Apart from nitrogen, phosphorus and potassium, other nutrient deficiencies causing significant yield losses are calcium, iron and boron. Biotic stresses mainly include pests, diseases, and weeds. Among insects pests, pod borers, aphids, and mites are of importance. The most important diseases are leaf spots, rusts, and the toxin-producing fungus Aspergillus.
In mechanized systems, a machine is used to cut off the main root of the peanut plant by cutting through the soil just below the level of the peanut pods. The machine lifts the "bush" from the ground, shakes it, then inverts it, leaving the plant upside down to keep the peanuts out of the soil. This allows the peanuts to dry slowly to a little less than a third of their original moisture level over three to four days. Traditionally, peanuts were pulled and inverted by hand. After the peanuts have dried sufficiently, they are threshed, removing the peanut pods from the rest of the bush.
Varieties
There are many peanut cultivars grown around the world. The market classes grown in the United States are Spanish, Runner, Virginia, and Valencia. Peanuts are produced in three major areas of the U.S.: the southeastern region which includes Alabama, Georgia, and Florida; the southwestern region which includes New Mexico, Oklahoma, and Texas; and in the general eastern U.S. which includes Virginia, North Carolina, and South Carolina. In Georgia, Naomi Chapman Woodroof is responsible for developing the breeding program of peanuts, resulting in a harvest almost five times greater.
The small Spanish types are grown in South Africa and the southwestern and southeastern United States. Until 1940, 90% of the peanuts grown in the U.S. state of Georgia were Spanish types, but the trend since then has been larger-seeded, higher-yielding, more disease-resistant cultivars. Spanish peanuts have a higher oil content than other types of peanuts. In the U.S., the Spanish group is primarily grown in New Mexico, Oklahoma, and Texas.
Pests and diseases
If peanut plants are subjected to severe drought during pod formation, or if pods are not properly stored, they may become contaminated with the mold Aspergillus flavus which may produce carcinogenic aflatoxins. Lower-quality and moldy peanuts are more likely to be contaminated. The USDA tests every truckload of raw peanuts for aflatoxin; any containing more than 15 parts per billion are destroyed. The industry has manufacturing steps to ensure all peanuts are inspected for aflatoxin.7 CFR 2011 – Part 996a Peanuts tested to have high aflatoxin are used to make peanut oil where the mold can be removed. The ant leaves can be affected by a fungus, Alternaria arachidis.
Production
+ Peanut production 19.2 10.3 4.3 2.7 1.4World54.3
In 2023, world production of peanuts (reported as groundnuts excluding shelled) was 54 million tonnes, led by China with 36% of the total and India with 19% (table).
Allergies