Peanut
The most surprising fact about peanut is not that it is a domesticated crop and cannot be found in the wild, or that more than 30 million tonnes are produced annually, or even that it has been taken into space. What is incredible about this plant is how the pod and seed develop. The yellow flowers are self-pollinated. After pollination, the flower stalk continues to grow, pushing the flower into the ground. Over three to four months the ovary matures underground to produce pods containing up to four seeds, the peanuts of commerce.
Arachis hypogaea, domesticated in Argentina and Bolivia, has been cultivated in South America for more than 3,500 years. Today, the largest commercial producers of peanuts are China, India and the United States. Modern varieties of Arachis hypogaea fall into two groups, either prostrate or erect, depending on how the plant grows. Commercial operations favour erect or bunching varieties that can be harvested by machine on an industrial scale, whereas varieties that are more prostrate are usually harvested by hand. Yellowing foliage indicates the time for harvesting and as Arachis hypogaea is an annual, the whole plant is lifted. These are left to dry on the surface of the soil with the pods attached for several days.
Peanut is a legume that is grown as part of crop rotation systems because of its ability to enrich the soil. Bacteria hosted on the roots of the plant fix nitrogen from the air and incorporate it into the soil. Consequently, peanut cultivation uses little nitrogen fertiliser. This and its efficient use of water means peanut is considered a sustainable crop when compared with maize and cotton, with which it is often cultivated. Post-harvest, peanut foliage can also be used as animal feed and the shells as fuel.
Good sources of oil, proteins, vitamins and minerals, make peanuts an important staple crop in many tropical and sub-tropical regions. Each nut contains around 50 percent oil, which is used for cooking oil, ghee and margarine. The seed is also rich in vitamins E and B complex. Peanuts are used extensively in cooking and are a popular high-energy snack, with each containing 30 percent protein. However, a small proportion of the population can experience severe allergic reactions to peanuts, even in tiny quantities.
Elvis Presley's favourite sandwich was peanut butter and banana, both of which grow in the glasshouses at Oxford Botanic Garden.
Further reading
Huxley A 1999. The new RHS dictionary of gardening. Macmillan Ltd.
Van Wyk B 2005. Food plants of the world. Timber Press.
Vaughan JG and Geissler CA 2009. The new Oxford book of food plants. Oxford University Press.
Kate Pritchard