The peanut (Arachis hypogaea) is native to central South America. By the time Columbus reached the New World, peanuts were already cultivated throughout warmer regions of the Americas. Peanuts have been introduced into Africa and Asian countries where they have become an important food crop. Like clover and alfalfa, the peanut root system contains nodules of nitrogen-fixing bacteria that convert inert atmospheric nitrogen into ammonia. Other bacteria convert the ammonia into nitrites and nitrates that enrich the soil with a usable form of nitrogen.

The peanut fruit is a dehiscent legume that is harvested from below the soil. The legume was originally formed above ground following pollination. After fertilization, the developing pod is forced down into the ground by the proliferation and elongation of a special structure called "peg" from cells below the ovary (called intercalary meristem by some authorities). The pod typically contains two seeds, each with a papery seed coat. Peanut seeds are eaten raw, salted and roasted. Peanuts are ground into peanut butter and Thai peanut sauce, and the expressed oil is used in cooking. Peanuts are also used in cookies, peanut brittle and candy bars.   Read About Aflatoxins In Moldy Peanuts   Question:   Considering double fertilization in angiosperms, how many sperm are involved in the formation of a mature 2-seeded peanut pod?

What I initially referred to as the flower stalk (pedicel) in my images was the hypanthium, sometimes called a floral tube or calyx tube. In fact, the peanut flower is sessile (or nearly so) in the leaf axil at base of plant. See: Rao V.R., Murty U.R. (1994) Botany — morphology and anatomy. In: Smartt J. (eds) The Groundnut Crop. World Crop Series. Springer, Dordrecht See This Reference On-Line. The long, tubular hypanthium extends above the ovary with petals at the tip.

Like other members of the subfamily Papilionoideae, the peanut flower (Arachis hypogaea) is papilionaceous, typical of a pea blossom. The flower is produced near the base of the plant. Each flower consists of five petals: a large banner, two lateral wings, and a keel formed by two fused petals. The keel petals enclose the 9 stamens (androecium) and pistil (gynoecium).

It should be noted here that some people have severe allergic reactions to peanuts. In a recent case in Quebec, a girl reportedly died after a seemingly harmless kiss from her boyfriend. In this case the girl was extremely allergic to certain proteins in peanuts, and the boy had just eaten a peanut butter sandwich. In severe reactions, the larynx swells shut and the victim is unable to breath, a condition known as laryngospasm. Another potentially life-threatening reaction from peanut hypersensitivity is anaphalactic shock. People with severe allergies to legumes and other kinds of nuts must read all food labels very carefully, especially if their child has this extreme hypersensitivity.

The mechanism for peanut hypersensitivity is a complex cell-mediated immune resonse involving white blood cells of the body's defense system against invading organisms. This is beyond the scope of my peanut page; however, I included a link to my poison oak page to show the amazing complexity of a cell-mediated immune response. It involves antigen-presenting dendritic cells similar to Langerhan's cells in the poison oak immune resonse. Other cells involved in the response include killer T-cells and memory cells. In the case of peanuts, the peanut protein allergen is recognized as a foreign pathogen by the body's immune system. I am quite certain that I have oversimplified this very serious immune response to peanuts.

The topic of aflatoxins in peanuts is another complex and controversial subject. In fact, I know of one microbiology professor who would not eat peanut butter because of this potential danger. Please see following link on this subject, especially if you need reassurance for eating peanut butter.

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