Peanuts

Peanut legumes have the peculiar habit of ripening underground, a phenomenon known as geocarpy. After pollination and the withering of the flower, an unusual stalklike structure called a peg grows from the base of the flower toward the soil. The fertilized ovules are carried downward in the sturdy tip of the peg until the tip is well below the soil surface, at which point the peg tip starts to develop into the characteristic pod. The pegs sometimes reach down 10 cm (4 inches) or more before their tips can develop fruits. These unusual fruits appear to function as roots to some degree, absorbing mineral nutrients directly from the soil. The pods may not develop properly unless the soil around them is well supplied with available calcium, regardless of the nutrients available to the roots.