Ground Nut, Peanut (Arachis hypogaea L)

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Taxonomic classification
Kingdom: Plantae
Division: Magnoliophyta
Class: Magnoliopsida
Subclass: Asteridae
Order: Solanales
Family: Leguminosae
Genus: Arachis
Species: A. hypogaea

Arachis is a small genus of about 40 species. Except A. hypogaea, all other species are wild and perennial. In all species, ripening of the fruits takes place underground.

  A.   hypogaesis is an annual herb, with erect or trailing habit. The plant is sparsely hairy and 15-60cm in height. The plant shows a dimorphic branching habit, with monopodial vegetative branches and reduced reproductive branches. In the first 3-5 nodes, monopodial branches arise, whereas, secondary monopodia may also arise from these branches. Reduced reproductive branches arise singly at nodes of monopodia. According to the arrangement of the monopodial vegetative and reduced reproductive branches, there are two distinct types of A. hypogaea. Alternate branches and sequential branches.

Cultivars of A. hypogaea can be divided into two sections,
   1)   Virginia- These are alternate branched forms
   2)   Spanish- Valencia- These are sequential branched forms

Morphological characters
Stem: Young Stems are solid and angular. Mature stems are hollow and cylindrical.
Roots: A well-developed tap root is present with many laterals. Nodules are found on the roots.
Leaves: The leaves are spirally arranged with a phyllotaxy of 2/5. The pinnately compound leaves have two opposite pairs of obovate leaflets. The stipules are prominent, linear-pointed and adanate to the petiole. Pluvinus can be seen at the point where stipules become free. The leaf apex is mucronate.

Flowers: The flowers are borne on compressed cymes with one to several flowers in single cymes. The flowers are sessile. The calyx forms a calyx tube and elongates as the bud develops. The calyx tube is very slender and often mistaken for pedicel.

Fruit: The fruit first appears at the end of a stalk-like structure known as the ‘peg’, which elongates and grows downwards penetrating the soil. Once the peg achieves maximum penetration, the ovary swells rapidly to form the fruit.
The mature fruit is a legume, which is structurally dehiscent, but functionally indehiscent. It is oblong with a dry reticulated pericarp with 10 longitudinal ridges. There are 1-6 seeds in a fruit.
The size, shape and color of testa (white, pink, red, purple and shades of brown) vary with the cultivar.

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