Arachis is a genus of roughly 70 species of annual and perennial flowering plants belonging to the family Fabaceae (order Fabales). All species are native to South America, where the genus originated in the region encompassing Bolivia, Argentina, Paraguay, and adjacent countries. Within Fabaceae, Arachis is placed in the tribe Dalbergieae, specifically in the informal monophyletic Pterocarpus clade.
The genus is overwhelmingly known for one species: the peanut, Arachis hypogaea, one of the world's most important food crops and a primary source of plant-based protein and edible oil globally. Beyond the cultivated peanut, several wild relatives are of significant agronomic interest. Arachis pintoi (pinto peanut) is grown worldwide as a pasture legume and ground cover, valued for its high-protein foliage and its ability to fix atmospheric nitrogen, making it useful in agroforestry and permaculture systems. A handful of other species are cultivated for food on a small scale within South America.
Arachis species are distinctive among legumes for their geocarpic fruiting habit — after fertilization the flower stalk (peg) elongates and pushes the developing pod into the soil, where the fruit matures underground. The genus also serves as a larval host for Lepidoptera including the flame shoulder moth, the nutmeg moth, and the turnip moth.
Etymology
The name Arachis derives from the ancient Greek arakos or arakis, a term applied to a leguminous plant, later Latinized and formally applied by Linnaeus to this South American genus when he described the peanut in 1753.
Distribution
Arachis is native exclusively to South America, with its center of diversity spanning Bolivia, Argentina, Paraguay, and southern Brazil. Arachis hypogaea has been cultivated and naturalized throughout tropical and subtropical regions worldwide since the Columbian Exchange.
Cultivation
The peanut (Arachis hypogaea) is a globally cultivated annual crop grown in tropical and warm-temperate regions, notable for its geocarpic habit in which pods develop underground after the fertilized flower stalk pushes into the soil. Arachis pintoi is widely cultivated as a perennial pasture legume and living mulch in agroforestry systems, where its nitrogen-fixing roots improve soil fertility. Other species are occasionally grown as forage or ornamental plants.
History
Arachis hypogaea was domesticated in South America — likely in the region of Bolivia or northwestern Argentina — several thousand years ago. It was carried throughout the Americas by indigenous peoples before European contact, then spread globally via the Columbian Exchange in the 16th century, becoming one of the most economically significant crops worldwide. The genus was formally described by Linnaeus in 1753.
