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Arachis hypogaea (Peanut, Groundnut)

Life > eukaryotes > Archaeoplastida > Chloroplastida > Charophyta > Streptophytina > Plantae (land plants) > Tracheophyta (vascular plants) > Euphyllophyta > Lignophyta (woody plants) > Spermatophyta (seed plants) > Angiospermae (flowering plants) > Eudicotyledons > Core Eudicots > Rosids > Eurosid I > Fabales > Family: Fabaceae > Subfamily: Papilionoideae

Arachis hypogaea (Peanut, Groundnut)
Arachis hypogaea (Peanut, Groundnut)
Arachis hypogaea (Peanut, Groundnut) Arachis hypogaea (Peanut, Groundnut)

Arachis hypogaea, Haslemere Lane, Umwinsidale, Zimbabwe. [photos Bart Wursten , Flora of Zimbabwe]

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

  • 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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