Common Name: Peanut

General Information

Peanut is an annual plant with erect or prostrate stems up to 70cm long. The root system consists of a well-developed taproot with many lateral roots, up to 135cm deep, but generally restricted to the upper layers of the soil[].
A very commonly used food plant, valued mainly for its edible seed and oil, but also having medicinal and other uses. It is widely cultivated throughout the tropics and sub-tropics for its seed, there are many named varieties[].

Known Hazards

Of greatest concern is possible contamination of damaged or spoiled seeds with the teratogenic, carcinogenic aflatoxins. Two principal toxins, aflatoxins B, and G, and their less toxic dihydro derivatives, aflatoxins B2 and G2 are formed by the aflatoxin producing moulds (Aspergillus flavus et al). Prevention of mould growth is the mainstay, there being no satisfactory way to remove the toxins from feed and foods (however, peanut oils are free of aflatoxins because of alkaline processing)[].

Botanical References

Range

S. America - possibly in the region of Paraguay, Bolivia, Argentina and Brazil.

Habitat

Not known in a truly wild state.

Properties

Edibility Rating
Medicinal Rating
Habit	Annual
Height	0.30 m
Pollinators	Insects
Self-fertile	Yes
Cultivation Status	Cultivated

Cultivation Details

Peanuts can be grown from the tropics to the warm temperate zone, with commercial crops succeeding between latitudes 40° south and 40° north[] and up to an elevation of 1,500 metres[]. Crops can be grown at further distances from the equator but yields are likely to be poor[]. Young growth is not frost-hardy and most cultivars require too long a growing season to make them a viable crop in most of the temperate zone. An average monthly temperature of 22 - 27°c produces the best crops, whilst growth ceases at about 15°c[, ]. An annual precipitation in the range 750 - 1,250mm is preferred, though as little as 500mm can be sufficient if well distributed[]. A distinct dry period is required to allow the seed to ripen[].
Prefers a light humus-rich well-drained soil in a warm sunny sheltered position, though it will tolerate heavier soils[, ]. Heavy clays and any soils that tend to form a crust or cap after rain are unsuitable since the fertilized flowers need to be able to penetrate the soil easily[]. Plants prefer hot dry conditions when the crop is ripening[]. Peanuts are quite tolerant of acid soils, and aluminium, requiring a minimum of lime for acceptable yields[]. Tolerates a pH in the range 4.3 to 8.7[], though around 6.5 is preferred[].
Yields average about 1 tonne of unshelled nuts per hectare, about 80% of this weight is edible seeds (erect forms) and 60 - 75% (running forms)[].
There are three main groups of cultivars:-
'Virginia' has large seeds.
'Valencia' has four seeds per pod.
'Spanish' has the smallest seeds[].
There are running and erect forms in each group[]. The erect forms mature more quickly and are therefore more likely to succeed in cooler areas[]. 'Early Spanish' matures in 105 days and has cropped reliably as far north as Canada[]. 'Spanish' matures in 110 days and crops in Canada if grown in a light sandy soil with southern exposure[].
Plants are, in general, self-pollinating, though occasional outcrossing by bees occurs[].
All types of peanut are daylength neutral and photoperiod does not appear to affect flower initiation[].
This species has a symbiotic relationship with certain soil bacteria, these bacteria form nodules on the roots and fix atmospheric nitrogen. Some of this nitrogen is utilized by the growing plant but some can also be used by other plants growing nearby[]. When removing plant remains at the end of the growing season, it is best to only remove the aerial parts of the plant, leaving the roots in the ground to decay and release their nitrogen.

Edible Uses

Seed - raw, cooked or ground into a powder. Peanuts are a staple food in many tropical zones and are widely exported to temperate area of the world. The seeds have a delicious nutty flavour and can be eaten on their own either raw or roasted[]. The seeds are commonly ground up and used as peanut butter in sandwiches etc[]. They can also be cooked in a variety of dishes and are also ground into a powder when they can be used with cereals to greatly improve the protein content of breads, cakes etc[]. The seed is very rich in protein and oil, it is also a good source of minerals and vitamins, especially the B complex[]. A nutritional analysis is available[].

A non-drying edible oil is obtained from the seed[]. This is one of the most commonly used edible oils is the world. It is similar in composition to olive oil and is often used in cooking, making margarines, salad oils etc[].

The presscake from oil extraction is rich in protein. It is made into groundnut flour, which is used in many human foods. Fermented groundnut cake is eaten fried in Indonesia[]. The oilseed cake is said to be a good source of arginine and glutamic acid, used in treating mental deficiencies[].

The roasted seed makes an excellent coffee substitute[, ].

Young pods may be consumed as a vegetable[, ].

Young leaves and tips are suitable as a cooked green vegetable[]. Javanese use the tips for lalab (a vegetable salad served with sambal), and germinating seeds to make toge[].

Medicinal

The oil from the seed is aperient, demulcent, emollient and pectoral[]. The seed is used mainly as a nutritive food[].
The seeds have been used in folk medicine as an anti-inflammatory, aphrodisiac and decoagulant[]. Peanuts play a small role in various folk pharmacopoeias. In China the nuts are considered demulcent, pectoral, and peptic; the oil aperient and emollient, taken internally in milk for treating gonorrhoea, externally for treating rheumatism[]. In Zimbabwe the peanut is used in folk remedies for plantar warts. Haemostatic and vasoconstrictor activity are reported. The alcoholic extract is said to affect isolated smooth muscles and frog hearts like acetylcholine. The alcoholic lipoid fraction of the seed is said to prevent haemophiliac tendencies and for the treatment of some blood disorders (mucorrhagia and arthritic haemorrhages) in haemophilia[].

Other Uses

The seeds yield a non-drying oil that has a wide range of uses including the manufacture of pharmaceuticals, soaps, cold creams, pomades and lubricants, paints, emulsions for insect control, and fuel for diesel engines[, ].

The presscake from oil extraction is rich in protein. It finds industrial application in the production of glues; sizes for paper; starches for laundering and textile manufacture[].
Protein from groundnut cake is made into a wool-like fibre, which can be blended with wool or rayon[].

The shells are used fir furfural, as fuel, fertilizer, mulch, in the manufacture of particle board and building blocks, and can be used as a source of activated carbon, combustible gases, organic chemicals, reducing sugars, alcohol and extender resins[, ].

Propagation

Seed - pre-soak for 12 hours in warm water and sow the seed in mid spring in a warm greenhouse. Germination should take place within 2 weeks. When large enough to handle, prick the seedlings out into individual pots of fairly rich soil and grow them on fast, planting them out after the last expected frosts and giving them some protection (such as a cloche) until they have settled down and are growing well.