The peanut or groundnut (Arachis hypogaea) is a species in the family Fabaceae (commonly known as the bean, pea or legume family). The peanut was probably first domesticated and cultivated in the valleys of Paraguay.It is an annual herbaceous plant growing 30 to 50 cm (1.0 to 1.6 ft) tall. The leaves are opposite, pinnate with four leaflets (two opposite pairs; no terminal leaflet); each leaflet is 1 to 7 cm (⅜ to 2¾ in) long and 1 to 3 cm (⅜ to 1 inch) across.
The flowers are a typical peaflower in shape, 2 to 4 cm (0.8 to 1.6 in) (¾ to 1½ in) across, yellow with reddish veining. The specific name, hypogaea means "under the earth"; after pollination, the flower stalk elongates, causing it to bend until the ovary touches the ground. Continued stalk growth then pushes the ovary underground where the mature fruit develops into a legume pod, the peanut – a classical example of geocarpy. Pods are 3 to 7 cm (1.2 to 2.8 in) long, containing 1 to 4 seeds.
Because, in botanical terms, "nut" specifically refers to indehiscent fruit, the peanut is not technically a nut, but rather a legume. Peanuts are often served in a similar manner to true nuts in many western cuisines, and are often referred to as a nut in common English.