Arachis hypogaea L.

Formal Description Naming

Arachis hypogaea L. was first formally described by Carl Linnaeus in his 1753 work Species Plantarum.

Growth Habit and Size

This species is an annual herbaceous plant that reaches a height of 30 to 50 centimetres, or 12 to 20 inches.

Taxonomic Classification

It is classified in the botanical family Fabaceae, which is also called Leguminosae, and is commonly known as the legume, bean, or pea family.

Root Symbiosis

As with other legumes, peanuts host symbiotic nitrogen-fixing bacteria in their root nodules.

Leaf Structure

Its leaves are opposite and pinnate, with four leaflets arranged in two opposite pairs with no terminal leaflet.

Leaflet Dimensions

Each individual leaflet measures 1 to 7 centimetres (1⁄2 to 2+3⁄4 inches) in length, and 1 to 3 centimetres (1⁄2 to 1+1⁄4 inches) across.

Leaf Movement Trait

Like the leaves of many other legumes, peanut leaves are nyctinastic, meaning they perform "sleep" movements and close at night.

Flower Characteristics

The flowers are 1 to 1.5 centimetres (3⁄8 to 5⁄8 inches) across, yellowish orange in color with reddish veining, and grow in axillary clusters on the plant's stems.

Geocarpic Fruit Trait

A defining unusual feature of peanuts is that their fruits develop underground, a trait called geocarpy.

Gynophore Development

After fertilization, a short stalk at the base of the ovary—often called a gynophore, which appears to be part of the ovary—elongates to form a thread-like structure called a "peg".

Peg Growth Function

This peg grows down into the soil, allowing the fruit to develop underground.

Pod Dimensions and Seed Count

The peanut pods, which are technically legumes, are 3 to 7 centimetres (1 to 3 inches) long, and normally contain between one and four seeds.

Fruit Shell Composition

The outer shell of the peanut fruit is made primarily of mesocarp, with several large veins running lengthwise through it.

Botanical Classification Clarification

Botanically, peanuts are not true nuts, which are defined as fruits where the ovary wall hardens at maturity.

Nutrient Composition

Peanuts contain polyphenols, polyunsaturated and monounsaturated fats, phytosterols, and dietary fiber in quantities that are similar to the levels found in many tree nuts.

Specialized Plant Compound

Resveratrol is found in peanut skins.