Chapter 2 - Biology, Speciation, and Utilization of Peanut Species

Abstract

Peanut, also known as groundnut (Arachis hypogaea L.), is a native new world crop. The Arachis species originated in South America and are found in tropical and subtropical areas. Eighty-one species have been named including the domesticated peanut, A. hypogaea L. Species have evolved in highly diverse habitats and both annual and perennial types exist. New species are being discovered in areas that previously were very difficult to reach because of poor roads and transportation. Fruiting below ground likely protected the seeds from predators and the many root adaptations (e.g., rhizomes, tuberous roots) likely helped species to adapt to new habitats. Conversely, the geocarpic fruit impeded rapid spread into new environments. The center of origin for A. hypogaea is believed to be southern Bolivia to northwestern Argentina based on the occurrence of the two progenitor species Arachis duranensis and Arachis ipaënsis, and archaeological evidence gathered in this region. Wild peanut species were important as sources of food in pre-Columbian times and several taxa are still widely used as forages or for their aesthetic value as a ground cover. Arachis glabrata and Arachis pintoi are utilized for grazing and Arachis repens is used as a ground cover in residential areas and roadsides in tropical regions. Two wild species (Arachis villosulicarpa and Arachis stenosperma) were cultivated by indigenous people in Brazil for food and medicinal use, albeit on a limited scale, but only A. hypogaea is economically important today as a human food source. Importantly, many Arachis species have extremely high levels of disease and insect resistances that are not present in cultivated peanut.