Nut (fruit)

A nut in botany is a one-seeded (rarely two) simple dry fruit 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 (do not open at maturity). Examples of true nuts are the fruits produced by walnut, oak (acorn), hazelnut (filbert), beech, chestnut, hickory, and butternut trees.

"Nuts" in cuisine are a much less restrictive category than nuts in botany, the term being misapplied 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.

Nuts are a significant source of nutrition for wildlife. This is particularly true in temperate climates where animals such as the squirrel store acorns and other nuts during the autumn to keep them from starving during the winter and early spring.

Nuts of temperate climates are dominated by wind-pollinated trees of the Order Fagales:

• acorn, the seed of the oak tree
• beech
• chestnut
• hazelnut or filbert, the seed of the hazel and cob trees
• hickory
• walnut, which includes English or Persian walnut, black walnut, heartnut, and butternut

Some "nuts" that are not true nuts in a botanical sense:

• almond; edible part is the seed of a drupe
• Brazil nuts are seeds from a capsule
• cashews are seeds
• coconut is a drupe
• horse chestnut is a capsule
• peanut, actually a bean; the fruit and seeds of a legume
• pecan; edible part is the seed of a drupe
• pine nut or piñon is the seed of a conifer

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. Most types of acorns are too bitter to eat unless leached, because of tannins. Despite this disadvantage, acorns are an important food in many regions.