The Peculiar Peanut

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Did you know that peanuts are not nuts at all? More accurately, they are a type of legume. What are you are actually eating are the cotyledons and embryo of the next generation of plants. Despite their popularity around the world, the plant itself gets very little attention outside of those interested in it for agricultural purposes. This is a shame as the ecology of the peanut is truly fascinating.

The plant that produces the peanuts that the world either loves or fears is known scientifically as Arachis hypogaea. It is originally native to South America and it is believed to have originally been domesticated in Paraguay over 7000 years ago. Domestic peanuts are amphidiploid or allotetraploid meaning they have two sets of chromosomes from two different parent species. 

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Research points to a natural hybridization event between Arachis duranensis and Arachis ipaensis, which produced the tetraploid Arachis monticola. It is A. monticola that gave rise to the domestic peanut we know today. As a plant, it looks rather much like most pinnate legumes. Its yellow flowers are unmistakably pea-like. It is only after they have been pollinated that they become truly bizarre. 

Members of this genus exhibit what is called "geocarpy." This relatively rare form of plant reproduction involves the plant literally planting its own seeds. After fertilization, the flower stalk elongates and bends towards the ground. Once it touches soil, the stalk pushes the developing seed pod down into the dirt. Underground, the seeds mature and germinate. The embryos will only become active in the dark, subterranean environment.

Photo Credit: Wikimedia Commons

Further Reading:

http://www.biomedcentral.com/content/pdf/1471-2164-14-517.pdf

http://www.amjbot.org/content/94/12/1963.abstract