From peas peas peas peas, picking goober peas:
"The plant is a trailing, bushy annual 20 to 30 centimeters tall with (usually) quadrifoliate leaves, large stipules, and runners (stolons). The flowers, usually yellow, are small and tend to be self-pollinated. About a week after fertilization takes place in the ovary, a meristem at the base of the ovary is activated. This meristem forms a stalk beneath the ovary, called a carpophore or, simply, a "peg." The stalk is positively geotropic (grows downward) and pushes the ovary toward the ground (pegging); the ovary tip hardens and is pushed into the sandy soil 3 to 10 centimeters. Belowground the ovary develops into the fibrous, tannish, indehiscent pod, a legume."