Arachis hypogaea (*)
Arachis hypogaea Linnaeus
* Species Plantarum 2:741. 1753
The peanut, or groundnut (Arachis hypogaea), is a species in the legume "bean" family (Fabaceae). The cultivated peanut was likely first domesticated in the valleys of the Paraguay and Parana rivers in the Chaco region of Paraguay and Bolivia. It is an annual herbaceous plant growing 30 to 50 cm (0.98 to 1.6 ft) tall. The leaves are opposite, pinnate with four leaflets (two opposite pairs; no terminal leaflet), each leaflet 1 to 7 cm (⅜ to 2¾ in) long and 1 to 3 cm (⅜ to 1 inch) broad. The flowers are a typical peaflower in shape, 2 to 4 cm (¾ to 1½ in) across, yellow with reddish veining. After pollination, the fruit develops into a legume 3 to 7 cm (1.2 to 2.8 in) long, containing 1 to 4 seeds, which forces its way underground to mature. Hypogaea means "under the earth."
Peanuts are known by many local names, including earthnuts, ground nuts, goober peas, monkey nuts, pygmy nuts and pig nuts. The term "Monkey nut" is often used to mean the entire pod. (The terms earthnut, groundnut and pignut can also refer to Conopodium majus or to tubers of the Bunium family.)
The domesticated peanut is an amphidiploid or allotetraploid, meaning that it has two sets of chromosomes from two different species. The wild ancestors of the peanut were thought to be A. duranensis and A. ipaensis, a view recently confirmed by direct comparison of the peanut's chromosomes with those of several putative ancestors. This domestication might have taken place in Paraguay or Bolivia, where the wildest strains grow today. In fact, many pre-Columbian cultures, such as the Moche, depicted peanuts in their art.
Archeologists have (thus far) dated the oldest specimens to about 7,600 years found in Peru . Cultivation spread as far as Mesoamerica where the Spanish conquistadors found the tlalcacahuatl (Nahuatl = "cacao", whence Mexican Spanish, cacahuate and French, cacahuète) being offered for sale in the marketplace of Tenochtitlan (Mexico City). The plant was later spread worldwide by European traders.
The legume gained Western popularity when it came to the United States from Africa. It had become popular in Africa after being brought there from Brazil by the Portuguese around 1800.
The orange veined, yellow petaled, pea-like flower of the Arachis hypogaea is borne in auxiliary clusters above ground. Following self-pollination, the flowers fade and wither. The stalk at the base of the ovary, called the pedicel, elongates rapidly, and turns downward to bury the fruits several inches in the ground, where they complete their development. When the seed is mature, the seed coat (mesocarp) changes color from white to a reddish brown. The entire plant, including most of the roots, is removed from the soil during harvesting.
The pods act in nutrient absorption. The fruits have wrinkled shells that are constricted between pairs of the one to four (usually two) seeds per pod. The mature seeds resemble other legume seeds such as beans, but they have paper-thin seed coats, rather than the usual, hard legume seed coats.
Peanuts grow best in light, sandy loam soil. They require five months of warm weather, and an annual rainfall of 500 to 1,000 mm (20 to 39 in) or the equivalent in irrigation water.
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.
Peanuts are particularly susceptible to contamination during growth and storage. Poor storage of peanuts can lead to an infection by the mold fungus Aspergillus flavus, releasing the toxic substance aflatoxin. The aflatoxin-producing molds exist throughout the peanut growing areas and may produce aflatoxin in peanuts when conditions are favorable to fungal growth.
Harvesting occurs in two stages. 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 and shakes it, then inverts the bush, leaving the plant upside down on the ground to keep the peanuts out of the dirt. This allows the peanuts to dry slowly to a bit less than a third of their original moisture level over a period of 3–4 days. Traditionally, peanuts are pulled and inverted by hand.
After the peanuts have dried sufficiently, they are threshed, removing the peanut pods from the rest of the bush.
The peanut was introduced to China by Portuguese traders in the 1600s and another variety by American missionaries in the 1800s. They became popular and are featured in many Chinese dishes, often being boiled. During the 1980s peanut production began to increase greatly so that as of 2006 China was the world's largest peanut producer. A major factor in this increase has been China's move away from a communist economic system toward a free market system so that farmers are free to grow and market their crops as they decide..
China leads in production of peanuts having a share of about 32.95% of overall world production, followed by India (18%) and the United States of America (6.8%).
Thousands of peanut cultivars are grown, with four major Cultivar Groups being the most popular: Spanish, Runner, Virginia, and Valencia. There are also Tennessee Red and Tennessee White groups. Certain Cultivar Groups are preferred for particular uses because of differences in flavor, oil content, size, shape, and disease resistance. For many uses the different cultivars are interchangeable. Most peanuts marketed in the shell are of the Virginia type, along with some Valencias selected for large size and the attractive appearance of the shell. Spanish peanuts are used mostly for peanut candy, salted nuts, and peanut butter. Most Runners are used to make peanut butter.
The various types are distinguished by branching habit and branch length. There are numerous varieties of each type of peanut. There are two main growth forms, bunch and runner. Bunch types grow upright, while runner types grow near the ground.
Each year new cultivars of peanuts are bred and introduced. Introducing a new cultivar may mean change in the planting rate, adjusting the planter, harvester, dryer, cleaner, sheller, and method of marketing.
The small Spanish types are grown in South Africa, and in the southwestern and southeastern U.S. Prior to 1940, 90% of the peanuts grown in Georgia, USA 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 and in the U.S. are now primarily grown in Oklahoma and Texas.
Cultivars of the Spanish group include "Dixie Spanish", "Improved Spanish 2B", "GFA Spanish", "Argentine", "Spantex", "Spanette", "Shaffers Spanish", "Natal Common (Spanish)", "White Kernel Varieties", "Starr", "Comet", "Florispan", "Spanhoma", "Spancross", "OLin", "Tamspan 90", "AT 9899-14", "Spanco" "Wilco I", "GG 2", "GG 4" and "TMV 2".
Since 1940, the southeastern U.S. region has seen a shift to production of Runner group peanuts. This shift is due to good flavor, better roasting characteristics and higher yields when compared to Spanish types leading to food manufacturers' preference for use in peanut butter and salting. Georgia's production is now almost 100% Runner type.
Cultivars of Runners include "Southeastern Runner 56-15", "Dixie Runner", "Early Runner", "Virginia Bunch 67", "Bradford Runner", "Egyptian Giant" (also known as "Virginia Bunch" and "Giant"), "Rhodesian Spanish Bunch" (Valencia and Virginia Bunch), "North Carolina Runner 56-15", "Virugard", "Georgia Green", "Tamrun 96", "Flavor Runner 458", "Tamrun OL01", "Tamrun OL02" and "AT-108".
The large seeded Virginia Group peanuts are grown in the following US states: Virginia, North Carolina, Tennessee, Texas, New Mexico, Oklahoma, and parts of Georgia. They are increasing in popularity due to demand for large peanuts for processing, particularly for salting, confections, and roasting in the shells.
Virginia Group peanuts are either bunch or running in growth habit. The bunch type is upright to spreading. It attains a height of 45 to 55 cm (18 to 22 in), and a spread of 70 to 80 cm (28 to 31 in), with 80 to 90 cm (31 to 35 in) rows that seldom cover the ground. The pods are borne within 5 to 10 cm of the base of the plant.
Cultivars of Virginia type peanuts include NC 7, NC 9, NC 10C, NC-V 11, VA 93B, NC 12C, VA-C 92R, Gregory, VA 98R, Perry, Wilson, Hull, AT VC-2 and Shulamit.
Valencia Group peanuts are coarse, and they have heavy reddish stems and large foliage. In the U.S. large commercial production is primarily in Eastern New Mexico, especially in and around Portales, New Mexico, but they are grown on a small scale elsewhere in the South as the best flavored and preferred type for boiled peanuts. They are comparatively tall, having a height of 125 cm (49 in) and a spread of 75 cm (30 in). Peanut pods are borne on pegs arising from the main stem and the side branches. Most of the pods are clustered around the base of the plant, and only a few are found several inches away. Valencia types are three seeded and smooth, with no constriction between the seeds. Seeds are oval and tightly crowded into the pods. There are two strains, one with flesh and the other with red seeds. Typical seed weight is 0.4 to 0.5 g.
Tennessee Red and Tennessee White groups
These are alike, except for the color of the seed. Sometimes known also as Texas Red or White, the plants are similar to Valencia types, except that the stems are green to greenish brown, and the pods are rough, irregular, and have a smaller proportion of kernels.
Edible peanuts account for two-thirds of the total peanut use in the United States. Popular confections include salted peanuts, peanut butter (sandwiches, candy bars, and cups), peanut brittle, and shelled nuts (plain/roasted). Salted peanuts are usually roasted in oil and packed in retail size, plastic bags or hermetically sealed cans. Dry roasted, salted peanuts are also marketed in significant quantities. Peanuts are often a major ingredient in mixed nuts because of their inexpensiveness compared to Brazil nuts, cashews, walnuts, and so on. The primary use of peanut butter is in the home, but large quantities are also used in the commercial manufacture of sandwiches, candy, and bakery products. Boiled peanuts are a preparation of raw, unshelled green peanuts boiled in brine and typically eaten as a snack in the southern United States where most peanuts are grown. More recently, fried peanut recipes have emerged - allowing both shell and nut to be eaten. Peanuts are also used in cosmetics, nitroglycerin, plastics, dyes and paints (See George Washington Carver).
Peanut oil is often used in cooking, because it has a mild flavor and a relatively high smoke point. Its high monounsaturated content makes it heart-healthy and resistant to rancidity. There are several types of peanut oil including: aromatic roasted peanut oil, refined peanut oil, extra virgin or cold pressed peanut oil and peanut extract. Studies have shown that refined peanut oil is safe for peanut allergic individuals because the protein is destroyed during the processing. In fact, in the United States, refined peanut oil is exempt from allergen labeling laws. 
Peanut flour is popular with culinary chefs because its high in protein content makes it an ideal flavor enhancer. Peanut flour is also used as a gluten-free solution and is lower in fat than peanut butter.
During Colonial times, the Spanish in Peru learned to use ingredients like peanuts in substitution for nuts which were unavailable in Peru. It is well documented that Spanish cuisine makes extensive use of almonds, pine nuts, and other nuts, in ground or paste form, combined with rice, meats and vegetables to create dishes like Rice Pilaf. However, almonds, pine nuts, chestnuts, walnuts, etc. were are too expensive or unobtainable in Peru. Peruvians have adapted by using nuts native to their region such as peanuts.
Although the peanut is not a nut, it may be argued that the Conquistadors used the peanut along with local Peruvian ingredients to emulate their ancestral cuisine in the absence of expensive almonds, chestnuts, walnuts and pine nuts.
In south Asian countries while generally they are known as either a light snack by themselves, usually roasted and salted, and often sold roasted in pod on roads in north or boiled with salt and sold in south, they are also made into little dessert or sweet snack pieces by processing with sugar and jaggery. Indian cuisine uses peanuts in roasted crushed form to give a crunchy body to salads and in leafy vegetable stews they are added whole (without pods) for the same reason. Most dishes in vegetarian cuisine use either coconut in fresh grated form or peanuts in whole or roasted and crushed form, generally not both.
Peanuts are also widely used in Southeast Asian cuisine, particularly Indonesia, where it is typically made into a spicy sauce. Peanuts originally came to Indonesia from the Philippines, where the legume came from Mexico in times of Spanish colonization.
Common Indonesian peanut-based dishes include gado-gado, pecel, karedok and ketoprak, all vegetable salads mixed with peanut sauce, and the peanut-based dipping sauce for satay.
In South Africa peanuts are believed to give males sexual vigor and to be an aphrodesiac.
The United States
In the US, peanuts are used in candies, cakes, cookies, and other sweets. They are also enjoyed roasted and salted. Peanut butter is one of the most popular peanut-based foods in the US.
Boiled peanuts are a popular snack in the southern United States, as well as in India and China. Peanuts are also used in the Mali meat stew maafe, and in many sauces for South American meat dishes, especially rabbit.
Peanuts are used to help fight malnutrition. Plumpy Nut and Medika Mamba are a high protein, high energy and high nutrient peanut-based paste that were developed to be used as a therapeutic food to aid in famine relief. Organizations like the World Health Organization, UNICEF, Project Peanut Butter and Doctors Without Borders have used these products to help save malnourished children in developing countries.
Peanuts can be used like other legumes and grains to make a lactose-free milk-like beverage, Peanut milk. Peanut plant tops are used for hay.
Low grade or culled peanuts not suitable for the edible market are used in the production of peanut oil. The protein cake (oilcake meal) residue from oil processing is used as an animal feed and as a soil fertilizer. Low grade peanuts are also widely sold as a garden bird feed.
Peanuts have a variety of industrial end uses. Paint, varnish, lubricating oil, leather dressings, furniture polish, insecticides, and nitroglycerin are made from peanut oil. Soap is made from saponified oil, and many cosmetics contain peanut oil and its derivatives. The protein portion of the oil is used in the manufacture of some textile fibers. Peanut shells are used in the manufacture of plastic, wallboard, abrasives, fuel, cellulose (used in rayon and paper) and mucilage (glue). Rudolf Diesel ran some of the first engines that bear his name on peanut oil  and it is still seen as a potentially useful fuel.
Peanuts are rich in nutrients, providing over 30 essential nutrients and phytonutrients. Peanuts are a good source of niacin, folate, fiber, magnesium, vitamin E, manganese and phosphorus. They also are naturally free of trans-fats and sodium, and contain about 25% protein (a higher proportion than in any true nut).
While peanuts are considered high in fat, they primarily contain “good” fats also known as unsaturated fats. One serving of peanuts contains 11.5 g unsaturated fat and 2 g of saturated fat. In fact, peanuts have been linked well enough to their heart-healthy benefits, in 2003, the Food and Drug Administration released a health claim recognizing peanuts in helping maintain your cholesterol.
The claim states: Scientific evidence suggests, but does not prove, that eating 1.5 ounces per day of most nuts, including peanuts as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease.
Some brands of peanut butter are fortified with Omega-3 in the form of flaxseed oil to balance the ratio of Omega-3 to Omega-6.
Peanuts are a good source of niacin and thus contribute to brain health and blood flow.
Recent research on peanuts and nuts in general has found antioxidants and other chemicals that may provide health benefits. New research shows peanuts rival the antioxidant content of many fruits. Roasted peanuts rival the antioxidant content of blackberries and strawberries, and are far richer in antioxidants than apples, carrots or beets. Research conducted by a team of University of Florida scientists, published in the journal Food Chemistry, shows that peanuts contain high concentrations of antioxidant polyphenols, primarily a compound called p-coumaric acid, and that roasting can increase peanuts' p-coumaric acid levels, boosting their overall antioxidant content by as much as 22%.
Peanuts are a significant source of resveratrol, a chemical studied for potential anti-aging effects and also associated with reduced cardiovascular disease and reduced cancer risk.
It has recently been found that the average amount of resveratrol in one ounce of commonly eaten peanuts (15 whole peanut kernels) is 73 μg. This means that, ounce for ounce, peanuts contain almost 30 times as much resveratrol as grapes, which often are touted as being one of the few good sources of the antioxidant.
Peanuts are a source of Coenzyme Q10, as are oily fish, beef, soybeans and spinach.
Some people (0.6% - 1% of the US population) have mild to severe allergic reactions. For some people with peanut allergy, exposure can cause fatal anaphylactic shock. For these individuals, eating a small amount of peanut or just breathing the dust from peanuts can cause a fatal reaction. An allergic reaction also can be triggered by eating foods that have been processed with machines that have previously processed peanuts, making the avoidance of such food difficult.
A theory of the development of peanut allergy has to do with the way that peanuts are processed in North America versus other countries like China and India. Peanuts are widely eaten in China and India but peanut allergies are almost unheard of there. According to a 2003 study, roasting peanuts, as more commonly done in North America, causes the major peanut allergen Ara h2 to become a stronger inhibitor of the digestive enzyme trypsin, making it more resistant to digestion. Additionally, this allergen has also been shown to protect Ara h1, another major peanut allergen, from digestion - a characteristic further enhanced by roasting.
Another theory, called the Hygiene hypothesis, states that a lack of early childhood exposure to infectious agents like germs and parasites, could be causing the increase of food allergies.
Recent (2008) studies comparing age of peanut introduction in Great Britain with introduction in Israel appear to show that delaying exposure to peanuts can dramatically increase the risk of developing peanut allergies.
Though the allergy can last a lifetime, another 2003 study indicates that 23.3% of children will outgrow a peanut allergy.
Peanut allergy has been associated with the use of skin preparations containing peanut oil among children, but the evidence is not regarded as conclusive. Peanut allergies have also been associated with family history and intake of soy products.
Some school districts in the U.S.A have banned peanuts,. There are experimental techniques which appear to have desensitized some allergic individuals.. The most popular technique, oral immunotherapy, works to create desensitization in those peanut allergic by feeding them small amounts of peanut until their body becomes desensitized.
Research indicates that refined peanut oil will not cause allergic reactions in most people with peanut allergies. However, crude (unrefined) peanut oils are strongly flavoured, and have been shown to contain protein, which may cause allergic reactions.
In a randomized, double-blind, crossover study, 60 people with proven peanut allergy were challenged with both crude peanut oil and refined peanut oil. The authors conclude that “Crude peanut oil caused allergic reactions in 10% of allergic subjects studied and should continue to be avoided.” They also state that, “Refined peanut oil does not seem to pose a risk to most people with peanut allergy.” However, they point out that refined peanut oil can still pose a risk to peanut-allergic individuals if oil that has previously been used to cook foods containing peanuts is reused.
Some progress is possibly being made in the UK:
Peanuts and aflatoxin
Peanuts may be contaminated with the mold Aspergillus flavus which produces a carcinogenic substance called aflatoxin. Lower quality specimens, particularly where mold is evident, are more likely to be contaminated. USDA tests every truckload of raw peanuts for aflatoxin, any containing aflatoxin levels of more than 20 parts per billion are destroyed. The peanut industry has manufacturing steps in place to ensure all peanuts are inspected for aflatoxin. Peanuts are also processed at a high temperature to ensure any microorganisms are killed.
U.S. Department of Agriculture (USDA) program
George Washington Carver is often credited with inventing 300 different uses for peanuts (which, contrary to popular belief, did not include peanut butter but did include salted peanuts). Carver was one of many USDA researchers who encouraged cotton farmers in the South to grow peanuts instead of, or in addition to cotton, because cotton had depleted so much nitrogen from the soil, and one of the peanut's properties as a legume is to put nitrogen back into the soil (a process known as nitrogen fixation). Rising demand for peanuts in the early 1900s was not due to Carver's products but to a shortage of plant oils during World War I and the growing popularity of peanut butter, roasted peanuts and peanut candies. Peanut products originating around the early 1900s include many brands still sold today such as Cracker Jack (1893), Planters peanuts (1906), Oh Henry! candy bar (1920), Baby Ruth candy bar (1920), Butterfinger candy bar (1923), Mr. Goodbar candy bar (1925), Reese's Peanut Butter Cup (1925), Peter Pan (peanut butter) (1928).
Peanuts were designated by the U.S. Congress to be one of America's basic crops. In order to protect domestic industry by keeping prices artificially high, the United States Department of Agriculture (USDA) aids peanut farmers through commodity programs. In the 2008 Farm Bill, the marketing quota for peanuts was eliminated and the Price Support Program was switched to a Direct and Counter-Cyclical Payment Program. Direct and counter-cyclical payments provide benefits to producers with eligible historical production of peanuts whenever the effective price is less than the targeted price.
The major producers/exporters of peanuts are the United States, Argentina, Sudan, Senegal, and Brazil. These five countries account for 71% of total world exports. In recent years, the United States has been the leading exporter of peanuts. The major peanut importers are the European Union (EU), Canada, and Japan. These three areas account for 78% of the world's imports.
Although India and China are the world's largest producers of peanuts, they account for a small part of international trade because most of their production is consumed domestically as peanut oil. Exports of peanuts from India and China are equivalent to less than 4% of world trade.
Ninety percent of India's production is processed into peanut oil. Only a nominal amount of hand-picked select-grade peanuts are exported. India prohibits the importation of all oil seeds, including peanuts.
The European Union is the largest consuming region in the world that does not produce peanuts. All of its consumption is supplied by imports. Consumption of peanuts in the EU is primarily as food, mostly as roasted-in-shell peanuts and as shelled peanuts used in confectionery and bakery products.
The average annual U.S. imports of peanuts are less than 0.5% of U.S. consumption. Two thirds of U.S. imports are roasted, unshelled peanuts. The major suppliers are Taiwan, Malaysia, Hong Kong, Mainland China, and Canada. The principal suppliers of shelled peanut imports are Argentina and Canada. Most of Canada's peanut butter is processed from Chinese peanuts. Imports of peanut butter from Argentina are in the form of a paste and must be further processed in the U.S. Other minor suppliers of peanut butter include Malawi, China, India, and Singapore.
Approximately 50% of all peanuts produced in the United States are grown within a 160 km (99 mi) radius of Dothan, Alabama. Dothan is home to the National Peanut Festival established in 1938 and held each fall to honor peanut growers and celebrate the harvest.
1. ^ "World Geography of the Peanut". Lanra.uga.edu. 2004-01-02. http://www.lanra.uga.edu/peanut/knowledgebase/. Retrieved 2009-08-18.
* Citizens Against Government Waste (CAGW), "Peanut Program"
Source: Wikispecies, Wikipedia: All text is available under the terms of the GNU Free Documentation License