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Arachis hypogaea (Peanut, Groundnut) Life
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> Spermatophyta (seed plants) > Angiospermae (flowering
plants) > Eudicotyledons > Core Eudicots > Rosids >
Eurosid I > Fabales > Family: Fabaceae > Subfamily: Papilionoideae
Groundnuts were domesticated by indigenous people in
the region of Argentina and Bolivia over 4000 years ago. The seedpods mature
underground, hence the name groundnuts. Peanuts are nutritious in that they
contain 45-50% oil and 25-30% protein as well as having certain vitamins.
However, peanuts infested with fungal aflatoxin and eaten in large quantities
can cause liver cancer in people.
Species in the genus Arachis have an interesting
reproductive biology because the seed-containing pods mature underground instead
of aerially as in most legumes. How does this happen? The flowers don't usually
open, and are self-pollinated. After pollination, there is cell division below
the young pod sending it down on a stalk and pushing it into the ground where it
matures. Once mature, the two halves of the pod, each containing a seed, are
pushed apart, so that the seeds grow separately in the soil. Burying the pod in
this way is apparently an adaptation for promoting seed survival in dry periods.
The Peanut Arachis hypogaea is a cultivar species
that was domesticated from the wild species A. monticola which is
native to northwest Argentina and southern Bolivia. Arachis hypogaea
differs from A. monticola in the following ways: (1) pods do not split
open underground; (2) some cultivars have more than two seeds per pod; (3)
seeds are larger; and (4) some cultivars are erect rather than prostrate.
In order to thrive, peanut plants need hot summers, with
alternating wet and dry seasons, and sandy soils.
Peanuts are nutritious in that they contain 45-50% oil and
25-30% protein as well as having certain vitamins. However, peanuts infested
with fungal aflatoxin and eaten in large quantities can cause liver cancer in
people.
The earliest archaeological records of peanuts show that
prior to 2000 BC they were being cultivated in Peru, outside their wild range.
By the time of the Spanish and Portuguese conquests of America, peanuts were
being grown widely in the West Indies and South America but not in Central and
North America. By the 1560's, peanuts had been introduced to West Africa
probably via slave ships. By the 1600's they were being widely grown in this
region. Peanuts became a particularly popular crop in Africa, Southeast Asia and
China.
Peanuts can be used in a variety of ways:
- nuts are roasted and eaten whole;
- oil is extracted and used for a variety of purposes.
The residual protein rich cake after oil extraction is used in food dishes
as well as a supplement for cattle;
- nuts are crushed and made into peanut butter;
- fermentation processes are used for producing certain
products.
References
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Sauer, J.D. 1993. Historical geography of
crop plants - a select roster. CRC Press, Boca Raton, Florida.
Text by Hamish G. Robertson
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