What Family is a Peanut In? The Definitive Guide to This Popular Legume

December 6, 2025 •

3 min read

While commonly referred to as a nut, a peanut is actually a legume, a surprising fact for many consumers. Belonging to the same family as peas, beans, and lentils, the peanut’s classification as a legume is a result of its botanical characteristics, including its underground growing habit.

Quick Summary

The peanut, or groundnut, belongs to the Fabaceae family, making it a legume and a close relative of peas and beans. Its fruit develops in an underground pod, unlike true nuts, which grow on trees.

Key Points

Botanical Classification: A peanut is a legume belonging to the Fabaceae family, putting it in the same group as peas and beans, not true nuts.
Underground Growth: Peanuts have a unique growth process called geocarpy, where the fertilized flower stalk (peg) grows downwards to bury and mature its pods underground.
Not a True Nut: Botanically, a nut is a hard-shelled fruit that doesn't split, while a legume, like the peanut, is a pod containing multiple seeds that does split open.
Distinct Allergies: Peanut allergies are distinct from tree nut allergies, although the severity can be similar, and they are often grouped together for caution.
Agricultural Benefits: Peanuts host nitrogen-fixing bacteria in their root nodules, which enriches the soil with nitrogen, making them beneficial for crop rotation.
Nutritional Similarities: Despite botanical differences, the nutritional profile of a peanut is comparable to tree nuts, providing a rich source of protein and healthy fats.

Unpacking the Peanut's Botanical Identity

Despite its 'nut' moniker and common culinary applications that mirror tree nuts, the peanut, scientifically known as Arachis hypogaea, is a member of the Fabaceae family, also known as the pea, bean, or legume family. This botanical classification is central to understanding its unique characteristics, from its growth cycle to its nutritional profile. The Fabaceae family is one of the largest plant families, encompassing a wide variety of flowering plants that produce their seeds in pods. Other notable members include soybeans, lentils, chickpeas, and alfalfa.

The Legume Distinction: Why Peanuts Aren't True Nuts

One of the most common points of confusion stems from the culinary use of peanuts versus their botanical reality. From a biological perspective, a true nut is a hard-shelled fruit containing a single seed, which does not split open on its own to release the seed. Examples of true nuts include acorns and hazelnuts. In contrast, a legume is a fruit that develops from a simple carpel and splits along two seams to release its seeds. A peanut fits this definition, growing inside a pod with multiple seeds. The pod of a peanut is merely a shell-like casing for the seeds within, aligning it with other legumes like peas and beans.

The Unique Growth Cycle: Geocarpy

The peanut plant has a fascinating and unusual growth process called geocarpy, a term that literally means "earth fruit". This sets it apart from many other legumes that produce their pods above ground. The process unfolds in several key steps:

Flowering: The peanut plant produces small, yellow, self-pollinating flowers on stems above the ground.
Pegging: After pollination, the stalk at the base of the ovary elongates, forming a thread-like structure called a 'peg'.
Burying: The peg, full of developing ovules, grows downward and pushes into the soil.
Maturation: Once safely underground, the tip of the peg develops into the familiar peanut pod, where the seeds mature.

This protective underground maturation helps shield the seeds from adverse conditions and animals, a clever adaptation that ensures successful reproduction.

Comparing Peanuts and Tree Nuts

While peanuts and tree nuts share culinary and nutritional similarities, their botanical and allergenic differences are important. Here is a comparison:


Feature	Peanut (Legume)	True Tree Nut (e.g., Acorn, Chestnut)
Botanical Family	Fabaceae (Pea/Bean Family)	Various families (e.g., Fagaceae)
Growth Location	Pods mature underground	Fruits grow on trees, above ground
Fruit Type	Legume (a pod with seeds)	True Nut (a hard-shelled fruit with a single seed)
Allergy Profile	Distinct from tree nut allergies, though commonly grouped due to similar severity	Specific allergens that differ from other nut groups
Nitrogen Fixation	Yes, hosts symbiotic bacteria in root nodules	No, does not possess this ability

A Valuable Agricultural Crop

Beyond being a dietary staple, the peanut serves a critical function in agriculture. Like most legumes, the peanut plant forms a symbiotic relationship with nitrogen-fixing bacteria in its root nodules. These bacteria convert atmospheric nitrogen into a form the plant can use, effectively fertilizing the soil. This capability makes peanuts a highly valuable crop for rotation farming, helping to replenish soil nutrients that are depleted by other crops, such as cotton. In many agricultural systems, planting peanuts can reduce the need for synthetic nitrogen fertilizers, making it a more sustainable and cost-effective option.

Conclusion

Ultimately, understanding what family a peanut is in means recognizing that this popular snack is botanically a legume, not a true nut. Its classification within the Fabaceae family aligns it with familiar foods like peas and beans and explains its unique geocarpic growth habit. This scientific distinction holds importance not only for botany enthusiasts but also for those with allergies, as peanut allergies are distinct from tree nut allergies. The peanut's fascinating journey from a flower above ground to a mature pod below the earth is a testament to its singular nature within the diverse world of plants.

Visit the Kew Gardens website for more botanical information on peanuts.

Frequently Asked Questions

A peanut is botanically a legume. While it is used culinarily like a nut, its classification is based on the fact that it is an edible seed that grows in a pod, like peas and lentils.

The Fabaceae family, also known as the legume, pea, or bean family, is a large family of flowering plants that produce their seeds in pods. It is the third-largest family of land plants.

Peanuts grow underground due to a process called geocarpy. After pollination, a stalk elongates and pushes the developing seed pod into the soil, where it matures safely.

No, peanut allergies are distinct from tree nut allergies. They are caused by different proteins. However, because allergic reactions can be similarly severe and cross-contamination is a risk, people with peanut allergies are often advised to also avoid tree nuts.

The root nodules on a peanut plant contain symbiotic nitrogen-fixing bacteria. These bacteria convert atmospheric nitrogen into usable nutrients for the plant and enrich the soil, which is beneficial for other crops in rotation.

A true nut is a hard-shelled fruit with a single seed that does not naturally split open. A legume is a fruit that is typically a pod with multiple seeds that splits open along two seams.

Other common legumes include peas, beans (such as kidney beans, black beans), lentils, chickpeas, and soybeans.