Legumes, plants belonging to the Fabaceae family, include some of the most important food crops worldwide. The question of whether these plants grow their fruit underground is common, and the answer depends on the specific species. While the vast majority produce their pods above the soil, a few notable members utilize a unique reproductive strategy that results in their fruit maturing beneath the surface.
Defining the Legume Family
A legume is botanically defined as a plant belonging to the Fabaceae family, which is the third-largest family of flowering plants in the world. This group is unified by a distinct fruit structure: a simple, dry pod that develops from a single carpel. This fruit typically splits open along two seams at maturity, a characteristic known as dehiscent, to release its seeds.
The term “legume” is often used to refer to the entire plant, the fruit, or the edible seeds housed inside, such as beans or peas. Although the family is diverse, containing nearly 20,000 known species, the shared pod structure is the defining feature.
The Majority Rule: Pods Maturing Above Ground
For the majority of species within the Fabaceae family, the reproductive cycle is conventional, with the fruit developing entirely above the soil. This standard process begins when a flower is pollinated while hanging from the plant’s stem or vine. The ovary within that flower then swells and develops into the mature pod.
Common examples like garden peas, lentils, soybeans, and most varieties of beans all follow this pattern of aerial maturation. The pods of these plants remain attached to the main plant structure and are fully exposed to the sun and air as the seeds inside grow and ripen. This straightforward process represents the baseline expectation for legume growth.
The Exception: The Process of Underground Maturation (Geocarpy)
A small group of legumes deviates from this standard by employing a specialized reproductive strategy called geocarpy, which means “earth fruit.” The most famous example of this is the peanut, Arachis hypogaea, also known as the groundnut. Unlike other legumes, the peanut plant pushes its developing fruit into the soil to mature.
The process begins normally with the plant flowering above ground, where the yellow flower is pollinated. After fertilization, the flower stalk elongates dramatically into a specialized organ called a gynophore, or “peg”. This peg exhibits a strong geotropic response, actively pushing the developing ovary at its tip into the soil.
Once the peg penetrates beneath the surface, the tip begins to swell and mature into the familiar peanut pod. This unique subterranean maturation offers a significant biological advantage, as it protects the developing seeds from harsh surface conditions like drought, heat, or certain pests. Geocarpy is a rare adaptation within the plant kingdom.