The classification of the peanut is often confusing, as peanuts are sold and consumed alongside tree nuts like almonds and walnuts, yet their name suggests a different origin. Determining whether the peanut is a bean, a nut, or something else entirely requires looking past common labels and into the world of botanical science. This confusion stems from the peanut’s unique growth habit and its culinary role.
The Botanical Truth: Peanuts are Legumes
From a scientific perspective, the peanut is not a true nut but a member of the bean, pea, or pulse family, known botanically as Fabaceae. This classification places the plant, Arachis hypogaea, in the same family as lentils, chickpeas, and soybeans. A legume is defined by its fruit: a simple, dry pod that develops from a single carpel and typically splits open at maturity to release its seeds.
The peanut seed is contained within a shell, which is technically the pod. Like other legumes, peanuts possess a symbiotic relationship with nitrogen-fixing bacteria. These bacteria reside in the plant’s root nodules and convert atmospheric nitrogen into a usable form. This biological feature fundamentally separates the peanut from botanically true nuts, which do not share this characteristic.
How Peanuts Grow
The peanut’s unconventional method of fruit production is the primary reason it is often mistaken for a root vegetable. Peanuts exhibit a unique biological process called geocarpy, which means “earth-fruiting.” This reproductive strategy separates the peanut from typical above-ground beans and tree nuts.
The process begins above ground with the pollination of small, yellow, pea-like flowers. After the flower withers, a specialized stalk-like structure called a peg, or gynophore, emerges from the base of the flower. This peg actively grows downward, pushing the fertilized ovary into the soil. Once the tip of the peg is safely buried underground, the ovary at the tip swells and matures into the familiar peanut pod.
Why We Call Them Nuts
The confusion surrounding the peanut’s identity is ultimately a matter of nomenclature, which is divided between botanical science and culinary application. Botanically, a true nut, such as an acorn or chestnut, is a hard-shelled, dry fruit that does not split open at maturity and is typically derived from a tree. Peanuts do not meet this strict definition, as their pod is not woody and they grow underground.
In the kitchen, the definition of a “nut” is much looser, focusing on texture, flavor, and use. Peanuts are used culinarily in the same way as tree nuts, such as for roasting, snacking, and grinding into butter. They share a similar nutritional profile with true nuts, being high in fat and protein, which contributes to their comparable texture and taste. This functional similarity is why peanuts are routinely grouped with tree nuts in commercial labeling and grocery store aisles.