Peanut pegs growing into the soil. The tip of the peg, once buried, swells and develops into a peanut fruit
Peanuts is an annual herbaceous plant growing 30 to 50 cm (1.0 to 1.6 ft) tall. As a legume, it 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 their root nodules. The leaves are opposite and pinnate
with four leaflets (two opposite pairs; no terminal leaflet); each
leaflet is 1 to 7 cm (⅜ to 2¾ in) long and 1 to 3 cm (⅜ to 1 in) across.
Like many other legumes, the leaves are nyctinastic, that is, they have "sleep" movements, closing at night.
Peanut pods develop underground, an unusual feature known as geocarpy. The flowers are 1.0 to 1.5 cm (0.4 to 0.6 in) across, and yellowish orange with reddish veining. They are borne in axillary
clusters on the stems above ground and last for just one day. The ovary
is located at the base of what appears to be the flower stem but is
actually a highly elongated floral cup. After fertilization, a short stalk at the base of the ovary (termed a pedicel)
elongates to form a thread-like structure known as a "peg". This peg
grows down into the soil, and the tip, which contains the ovary,
develops into a mature peanut pod. Pods are 3 to 7 cm (1.2 to 2.8 in) long, normally containing one to four seeds.
Parts
Parts of the peanut include:
- Shell - inedible outer covering, in contact with dirt
- Cotyledon - main edible part
- Seed coat - brown papery covering of the edible part
- Radicle - embryonic root at the bottom of the cotyledon, which can be snapped off
- Plumule - embryonic shoot emerging from the top of the radicle
Industrial use
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 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).
