Peanut, also known as groundnut (Arachis hypogaea) is a crop of global importance. It is widely grown in the tropics and sub-tropics, being important to both smallholder and large commercial producers. It is classified as both a grain legume, and, because of its high oil content, an oil crop. World annual production is about 46 million tonnes per year. China accounts for 37% of World production, Africa for 25%, India for 21% and the Americas 8%. In Africa, remarkably, its production exceeds that of all other grain legumes put together, and it is an extremely important source of protein, energy and iron (Production Statistics from 2013).As a legume, peanut belongs to the botanical family Fabaceae (also known as Leguminosae, and commonly known as the bean or pea family). Like most other legumes, peanuts harbor symbiotic nitrogen-fixing bacteria in root nodules. This capacity to fix nitrogen means peanuts require fewer fertilizers and improve soil fertility, making them valuable in crop rotations. It also accounts for the high protein content of peanut seeds. It is an annual herbaceous plant growing 30 to 50 cm (1.0 to 1.6 ft) tall. The leaves are opposite and 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. Like many other legumes the leaves are nyctinastic, that is they have ""sleep"" movements, closing at night.The specific name, hypogaea means ""under the earth"", referring to the fact that peanut pods develop underground, a feature known as geocarpy. The flowers are 1 to 1.5 cm (0.4 to 0.6 in) across, and yellowish orange with reddish veining. In structure they appear superficially similar to the flowers of peas and beans. However, there are intriguing differences. The ovary is not, as expected, enclosed by the petals, but is at the base of what appears to be the flower stalk. In fact, this ""stalk"" is a hollow structure named a hypanthium, through which runs the style and at the base of which, is the ovary. After fertilization a stalk (termed a pedicel) at the base of the ovary elongates to form a thread-like structure known as a ""peg"". This pushes the ovary down into the soil were it develops into a mature peanut pod. Pods are 3 to 7 cm (1.2 to 2.8 in) long, normally containing 1 to 4 seeds.Peanuts are similar in taste and nutrional profile to tree nuts such as walnuts, pecans, hazelnuts, and almonds and they are often served in a similar ways in many western cuisines. In long term studies, the regular consumption of peanuts and tree nuts has been associated with health benefits including the reduction in heart and respiratory diseases and cancer. Interestingly, the botanical definition of a ""nut"" is a fruit whose ovary wall becomes very hard at maturity. Using this criteria the peanut is not a nut, but rather a legume. However for culinary purposes and in common English language usage, peanuts are usually referred to as nuts.