There are over 70 species in Arachis genus, most are diploid, only one species Arachis hypogaea, called peanut or groundnut, a tetraploid species which is widely cultivated in world. Arachis hypogaea was believed to be originated from a single hybridization event between two probable progenitors, A. duranensis (AA genome) and A. ipaensis (BB genome), followed by chromosome duplication, gave rise to a wild allotetraploid (plausibly the still extant Arachis monticola). These species and a few other important relatives are used as sources of disease resistance, quality and environment tolerance. A. hypogaea was now widely cultivated for over 100 countries worldwide and derived into two suspecies of 6 ecotypes (varieties). A. h. subsp. fastigiata var. vulgaris and A. h. subsp. hypogaea var. hypogaea are the widest cultivated in the world. The var. vulgaris, market type as Spanish, originated from areas of Brazil, Paraguay and Uruguay, are mainly and widely cultivated in Acia and Africa, especially in China and Idia, etc. takes about 80% of the total world peanut growing area. Var. hypogaea, market types as Virginia or Runner, originated from Bolivia-Amazon, widely somesticated in middle and south America takes about 15% of the total peanut growing area. There are also other varieties in the two subspecies who are long been cultivated as landraces in small area in the world. However, other species now are still not exploited. More about cultivated peanut: a short description of Cultivated Peanut Origins (PDF), taxonomy of the genus Arachis (PDF), and a description of Chinese peanut production in 2004 (PDF)

Browse genome
Description:
Cultivated peanut, botanically named as Arachis hypogaea (also known as or groundnut, earthnuts, goober peas, etc.), is a legume crop grown in the tropics and subtropics mainly for its seeds and the oil. It is classified as a grain legume with high oil content, rich protein and a good source of vitamins and minerals. It is an important oil crop with a total global production area of some 59 million acres, producing 42 million tonnes of shelled peanut in 2014. China is a biggest peanut producer, producing 17.91 million tonnes of peanuts annually by 2014（http://www.chyxx.com/）, which takes about 42.34% of world’s total output. Peanut is grown nearly all over China excepting two inland provices, Qinhai and Ningxia. The agronomical producer value ranks the fourth of all crops grown in China, after the three main crops, rice, wheat, and corn.

    The peanut belongs to the botanical family Fabaceae, also known as Leguminosae. Like most other legumes, peanuts harbor symbiotic nitrogen-fixing bacteria in root nodules. This capacity to fix nitrogen makes peanuts require less nitrogen fertilizer and will improve soil fertility, which is valuable in crop rotations and was taken as a pioneer crop for new arable land.

    The peanut is an annual herbaceous plant in the Fabaceae. After pollination, the flower stalks elongate, growing to about 6 cm long, and push the developing pods into the ground. Although referred to as a nut, it is actually the underground pod of a legume, rather than a true nut. The fruit is an indehiscent legume,usually containing 1 to 3 soft seeds, sometimes 6 to the most. Numerous cultivars have been developed, which have different growth forms, size, shape, flavor, and disease and insect resistance; the varieties are generally classified into four major groups, two upright (Valencia and Spanish), and two with prostrated plants (Virginia and Peruvian).

    As an oil crop, peanut seeds contain about 50% oil. Peanuts are also high in protein and vitamin B and E, as well as minerals. Peanut kernels/seeds are eaten raw or boiled and roasted (and often salted) as a snack, and they are cooked in a wide variety of Asia, African, and South American dishes (ranging from a great many of processings, soups, stews and curries, as well as used in confections. They are frequently ground into peanut butter in American, or pressed for the oil in Asia, which is used in cooking, salad dressings, margarine, and mayonnaise, as well as in the manufacture of soaps and cosmetics. The seeds, pods, and whole plants are also a source of animal fodder, fiber for paper production, and a green fertilizer. There are several hundrads different processings in China.

    Cultivated peanut (A. hypogaea) arose from single hybrid between two wild species of peanut, probably A. duranensis and A. ipaensis, forming an amphidiploid or allotetraploid. A. monticola, a wild form of peanut, was believed to be the first form of hybridization, restricted in north western Argentina, and late evolved into A. hypogaea by artificial selection. Domestication was first in northwestern Argentina, or in southeastern Bolivia as the primary center, which made A. hypogaea changes in plant and pod structure with larger seeds. Cultivation then spread to Peru, Ecuador, Brazil, Paraguay, and Uruguay, which formed the secondary and tertiary centers of diversity . A great many landraces are classified into six botanical varieties and two subspecies. Subspecies A. h. fastigiata types are 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. It was certain that cultivation was well established in Mesoamerica before the Spanish arrived. The peanut was later spread worldwide by European traders. Cultivation is now very widespread in tropical and subtropical regions. Now peanut became the mainstay in Africa and Asia. These regions is now the first and second producers in the world, taking 65% and 25% of total world output.

    In China, the mordern version of peanut was first recorded in 1638 of Ming Dynasty after Christopher Columbus discovered the Americas. The next record is in the middle of the 19th century by American missionaries.Then the crop spread to all provinces of the country. Based on ecological zoning, the peanuts producing areas were divided into seven regions in China, ranging from the frigid north to the humid south of China, and from the eastern to western region, and China became the world biggest producer of peanut.

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Description:
Cultivated peanut (A. hypogaea) derived from a hybrid between two wild species of peanut, A. duranensis and A. ipaensis, forming an allotetraploid species.There are a great many landraces during domestigation andare classified into six botanical varieties and two subspecies. Subspecies A. h. hypogaeatypes, botanically containing var. hypogaea and var. hirsuta, have the characteristics of phenotypes: no flowers on the mainstem; alternating pairs of floral and reproductive nodes on lateral branches; branches short; relatively few trichomes.The market types include Virginia and Runner.

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重测序
Description:
Subsp. A. h. hypogaea var. hypogaea, evolved from Amazon, Bolivia. The market types, Virginia type peanuts are either bunch or running in growth habit. Runner type being small seeds and less hairy.This varieties are widely used in north and south American with high yield.

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重测序
Description:
Subsp. A. h. hypogaea var. hirsuta, such as peruvian runner, evose from Peru, has hairy leaf and stem, usually conting more than two seeds in one pod.

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Description:
Subspecies A. h. fastigiata including four varieties, var. fastigiata, var. vulgaris, var. peruviana and var. eaquatoriana, have the characteristics of phynotype: flowers on mainstem; sequential pairs of floral and vegetative axes on branches. The famous market types are Spanish and valencia,which are widely cultivated all over the world.

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重测序
Description:
Subsp. A. h. fastigiata var. fastigiata derived from Guanaian, Goias or Minas Gerais of Brazil, Paragury, Peru and Uruguray, has little branched or curved branches. The market type valenciaare three- to five-seeded and smooth, with no constriction of the shell. Seeds are tightly crowded into the pods. They have heavy reddish stems and tall plants.

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重测序
Description:
Subsp. A. h. fastigiata var. vulgaris derived from Guaranian, Goias or Minas Gerais of Brazil, Paraguay and Uruguay, containing more brantches and upright brantches. The market type Spanish peanuts have a higher oil content than other types of peanuts. The Spanish group is primarily grown in Asia and Africa, also in south America, the growing area takes more than 80% of world peanut planting area.

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Browse genome
Description:
A. monticola, a wild amphidiploids species of peanut with AABB genome,which was suggested by genetic research as the early hybridization of two wild species, A. duranensis and A. ipaensis. A. mondicola were found in a few restricted locations in northwestern Argentina, where it evolved into cultivated peanut by artificial selections.

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Browse genome (GBrowse) at PeanutBase
Browse genome (JBrowse) at PeanutBase
Description:
A. ipaensis is a diploid wild species of Arachis genus containing BB genome and it is one of the ancestor of cultivated peanut, who had hybridized with the A. ipaensis by a random event, which evolve into modern allotetraploid peanut after spontaneous chromosome doubling and by artificial selection and cultivation.

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Description:
A. batizocoi is a diploid wild species of Arachis genus with BB genome and is close related to cultivated peanut. Now it is used as material of research for cultivated peanut and source of some resistance.

Browse genome (GBrowse) at PeanutBase
Browse genome (JBrowse) at PeanutBase
Description:
A. duranensis is a diploid wild species of Arachis genus containing AA genome and is believed to be one of the ancestor of cultivated peanut. It had hybridized with A. ipaensis by a random event, which evolve into modern allotetraploid peanut after spontaneous chromosome doubling and by artificial selection and cultivation.

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Description:
A. stenosperma is a wild relative of the groundnut with AA genome, and has a peculiar disjunct distribution in Central Brazil and along the Atlantic coast. A. stenosperma was used as a new Source of Nematode Resistance for Peanut.

Description:
A. cardenasii is a wild relative of the groundnut with AA genome. It is used as gene sources for research in plant biology of peanut, for example, Cercospora leaf spot resistance.