Peanut plants (Arachis hypogaea) produce flowers and are members of the legume family (Fabaceae). This annual herb grows low to the ground, but its reproductive cycle is highly unusual. It flowers above the soil but sets its fruit underground, a process known as geocarpy, which sets it apart from nearly all other flowering species.
The Appearance and Location of Peanut Flowers
Peanut flowers typically measure between 1 and 1.5 centimeters across. The blossoms are yellowish-orange, sometimes featuring subtle reddish veins. Their structure is characteristic of the pea family, described as papilionaceous, meaning they are shaped like a butterfly with five petals.
The flowers emerge low on the plant, often near the stem base. They appear 30 to 40 days after the seed germinates and are typically self-pollinating. A single flower blooms for just one day, with the petals falling off shortly after fertilization occurs.
From Flower to Peg: The Unique Reproductive Process
After the flower is fertilized, the ovary at the base of the flower elongates rapidly, forming a specialized stalk known as a gynophore, or “peg.” This peg is a modified stem-like structure, not a root, with the developing embryo located at its tip.
The peg exhibits positive geotropism, meaning it grows downward, away from light and toward the earth. This specialized stalk pushes through the air and soil surface, carrying the fertilized ovary. Its sharp tip allows it to penetrate the soil to a shallow depth, usually between one and seven centimeters. The physiological changes are precisely regulated to drive this downward growth.
Developing the Peanut Pod Underground
Once the peg penetrates the soil, the tip containing the fertilized embryo halts its downward growth and begins to swell. It then turns horizontally, and the process of pod and seed development accelerates.
Mature peanut pods require specific environmental conditions within the soil, including darkness and consistent moisture. Developing pods also require specific nutrients, such as calcium, which are absorbed directly through the peg and pod shell. The best growth occurs in loose, sandy loam soil, which allows the peg to penetrate easily.
Maturation typically takes around 70 days after the peg is buried. The entire cycle from planting to harvest can range from 100 to 150 days, depending on the variety and climate. Since the plant produces flowers and pegs over several weeks, a single plant will have pods at various stages of development. This necessitates a specialized harvesting method where the entire plant is dug up and inverted to expose the mature, soil-covered pods.