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Peanut, also known as groundnut (''Arachis hypogaea'') is a crop of global importance. It is widely grown in the tropics and subtropics, being important to both smallholder and large commercial producers. It is classified as both a grain legume, and, because of its high oil content, an oil crop. World annual production is about 46 million tonnes per year. Very unusually among crop plants, peanut pods develop under the ground. As a legume, peanut belongs to the botanical family Fabaceae (also known as Leguminosae, and commonly known as the bean or pea family).〔 Like most other legumes, peanuts harbor symbiotic nitrogen-fixing bacteria in root nodules. This capacity to fix nitrogen means peanuts require less nitrogen-containing fertilizer and improve soil fertility, making them valuable in crop rotations. Peanuts are similar in taste and nutritional profile to tree nuts such as walnuts and almonds, and are often served in similar ways in Western cuisines. The botanical definition of a "nut" is a fruit whose ovary wall becomes very hard at maturity. Using this criterion, the peanut is not a nut,〔(【引用サイトリンク】title=The Peanut Institute – Peanut Facts )〕 but rather a legume. However, for culinary purposes and in common English language usage, peanuts are usually referred to as nuts. ==History== Cultivated peanut (''A. hypogaea'') has two sets of chromosomes from two different species, thought to be ''A. duranensis'' and ''A. ipaensis''.〔〔 The two species' chromosomes combined by hybridization and doubling, to form what is termed an amphidiploid or allotetraploid. Genetic analysis suggests this hybridization event probably occurred only once and gave rise to ''A. monticola'', a wild form of peanut that occurs in a few restricted locations in northwestern Argentina, 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 more bushy and compact, and have a different pod structure and larger seeds. The initial domestication may have taken place in northwestern Argentina, or in southeastern Bolivia where the peanut landraces with the most wild-like features are grown today. From this primary center of origin cultivation spread and formed secondary and tertiary centers of diversity in Peru, Equador, 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 ''fastigiata'' types are more upright in their growth habit and have a shorter crop cycles. Subspecies ''hypogaea'' types spread more on the ground and have longer crop cycles.〔〔 It is difficult to estimate the date of peanut's domestication. The oldest known archeological remains of pods have been dated at about 7,600 years old. These may be pods from a wild species that was in cultivation, or ''A. hypogaea'' in the early phase of domestication.〔(【引用サイトリンク】 Earliest-known evidence of peanut, cotton and squash farming found )〕 They were found in Peru, where dry climatic conditions are favorable to the preservation of organic material. It is almost certain that 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 and Hudson, 1997.〕 Cultivation was well established in Mesoamerica before the Spanish arrived. There the conquistadors found the ''tlalcacahuatl'' (the plant's Nahuatl name, whence Mexican Spanish ''cacahuate'', Castillian Spanish ''cacahuete'', and French ''cacahuète'') being offered for sale in the marketplace of Tenochtitlan. The peanut was later spread worldwide by European traders and cultivation is now very 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. In Asia it became an agricultural mainstay and this region is now the largest producer in the world.〔 In the English-speaking world peanut growing is most important in the U.S.A. Although it was mainly a garden crop for much of the colonial period, it was mostly used as animal feed stock until the 1930s.〔Putnam, D.H., et al. (1991) (Peanut ). University of Wisconsin-Extension Cooperative Extension: Alternative Field Crops Manual.〕 The US Department of Agriculture initiated a program to encourage agricultural production and human consumption of peanuts in the late 19th and early 20th centuries. George Washington Carver developed hundreds of recipes for peanuts during his tenure in the program. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「peanut」の詳細全文を読む スポンサード リンク
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