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Are peanuts true nuts?
Peanuts grow underground in pods and belong to the bean family.
Botanists use a narrow definition of a nut: a dry fruit with a hard wall that does not split open to release its single seed, as in hazelnuts and chestnuts. The peanut, Arachis hypogaea, does not fit. Britannica identifies it as the pod of a plant in the legume family, Fabaceae, which also contains beans, peas and lentils. Its pod does split along seams, and it holds more than one seed, which is typical of legumes.
The peanut has an unusual growth habit called geocarpy. After a flower is pollinated and wilts, a stalk-like structure called a peg grows downward from the flower base and pushes into the soil. The fertilized ovules at its tip then develop into a pod beneath the ground, which is why the plant is also called groundnut. Britannica notes that pegs can extend 100 millimeters or more, and that the developing pods need adequate calcium in the surrounding soil. Plant scientists have studied the genes behind this behavior, since few crops fruit underground.
The plant is native to tropical South America and spread to Africa, Asia and elsewhere after early contact, and it is now a major crop in India, China, West Africa and the United States. The nut label is a culinary and commercial one, as peanuts are cooked and eaten much like tree nuts. A related point is that allergy to peanuts and to tree nuts are separate conditions, though they may occur together in the same person; that is reported in medical literature but is not covered in the sources used here. Whether a plant counts as a nut depends on the botanical definition used.