Botanical definition

A nut in botany is a simple dry fruit with one seed (rarely two) in which the ovary wall or part of it becomes very hard (stony or woody) at maturity. Most nuts come from pistils with inferior ovaries (see flower) and all are indehiscent (not opening at maturity). True nuts are produced by plants in the order Fagales; note that not all true nuts are edible; some (e.g. birch, alder, hornbeam, wingnut) are too small to be worth eating, while others (e.g. tanoak) are too bitter to be edible.

Order Fagales

• Family Juglandaceae
  • Walnut, Butternut (Juglans)
  • Hickory, Pecan (Carya)
  • Wingnut (Pterocarya)
• Family Fagaceae
  • Chestnut (Castanea)
  • Beech (Fagus)
  • Oak (Quercus)
  • Stone-oak, Tanoak (Lithocarpus)
• Family Corylaceae
  • Hazel, Filbert (Corylus)
  • Hornbeam (Carpinus)
• Family Betulaceae
  • Birch (Betula)
  • Alder (Alnus)

Culinary definition and uses

A nut in cuisine is a much less restrictive category than a nut in botany, the term being applied (or misapplied, depending upon the viewpoint) to many seeds that are not true nuts. Any large, oily kernel found within a shell and used in food may be regarded as a nut. Because nuts generally have a high oil content, they are a highly prized food and energy source. A large number of seeds are edible by humans and used in cooking, eaten raw, sprouted, or roasted as a snack food, or pressed for oil that is used in cookery and cosmetics. By the same token, nuts (or seeds generally) are a significant source of nutrition for wildlife. This is particularly true in temperate climates where animals such as jays and squirrels store acorns and other nuts during the autumn to keep them from starving during the winter and early spring.

Korean Pine pine nuts - unshelled, and shell, above; shelled, below

Some fruits and seeds that are "nuts" in the culinary sense but not in the botanical sense:

• Almond, is the edible seed of a drupe - the leathery "flesh" is removed at harvest.
• Pistachio nut is the seed of a thin-shelled drupe.
• Brazil nuts are seeds from a capsule.
• Cashew nuts are seeds.
• Coconut is a dry fiberous drupe.
• horse-chestnut (not edible!) is a capsule.
• Peanut is a legume.
• Pine nuts are the seeds of several species of pine (coniferous trees).
• Candle nut (used for oil) is a seed.

See also: List of edible seeds

Nut allergy

Allergy to nuts is a relatively frequent, and often very serious problem. For people with nut allergy, exposure to surprisingly small amounts of nut fragments (e.g. minor cross-contamination of otherwise nut-free products in a food processing factory) can cause fatal anaphylactic shock.

Allergy to peanuts is the most common; some evidence suggests that peanut allergy may be related to the use of peanuts in baby foods; if given to very young children who are not yet able to digest all the components of peanuts fully, the body will then react against those components. As the peanut is a member of the pea family unrelated to other nuts, individuals with allergies to peanuts may not be allergic to other nuts, and those with allergies to other nuts may not be allergic to peanuts.

Other uses

The "nut" of the horse-chestnut, (Aesculus hippocastanum), is also known as a conker. Conkers are inedible but are collected and used in an old children's game, also known as conkers, in which a nut is threaded onto a strong cord and then each child attempts to break their opponent's conker by hitting it with their own. A related species, Aesculus californica, was formerly eaten by the Native Americans of California in times of famine. It must be leached to remove poisonous constituents before eating.