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How do peanut fruits develop underground?

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Yellow partridge pea — Fabales A flowering stalk of yellow partridge pea (*Chamaecrista fasciculata*) in the eastern United States.

Peanut fruits develop underground through a unique process known as geocarpy, where the plant actively buries its developing fruits.12

After pollination occurs and the flower withers, a specialized, stalklike structure called a peg emerges from the base of the flower. This peg grows downward toward the soil, carrying the fertilized ovules within its sturdy tip. The peg may extend as far as 10 cm (4 inches) or more into the ground. Once the tip is buried, it begins to develop into the characteristic peanut pod.1

These developing fruits function similarly to roots by absorbing mineral nutrients directly from the soil. For the pods to develop properly, the surrounding soil must be well supplied with calcium, which is essential regardless of the nutrients available to the plant's primary root system.1