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A nut is a fruit composed of a hard shell and a seed, which is generally edible. In botany, there is an additional requirement that the shell does not open to release the seed (indehiscent). In a general context, a wide variety of dried seeds are called nuts, but in a botanical context, only ones that include the indehiscent fruit are considered true nuts. The translation of "nut" in certain languages frequently requires paraphrases, as the word is ambiguous. Most seeds come from fruits that naturally free themselves from the shell, unlike nuts such as hazelnuts, chestnuts, and acorns, which have hard shell walls and originate from a compound ovary. The general and original usage of the term is less restrictive, and many nuts, such as almonds, pecans, pistachios, walnuts, and Brazil nuts, are not nuts in a botanical sense. Common usage of the term often refers to any hard-walled, edible kernel as a nut. == Botanical definition == A nut in botany is a simple dry fruit with one seed (rarely two) in which the ovary wall becomes very hard (stony or woody) at maturity, and where the seed remains unattached or free within the ovary wall. Most nuts come from the pistils with ''inferior'' ovaries (see flower) and all are ''indehiscent'' (not opening at maturity). True nuts are produced, for example, by some plant families of the order Fagales. ;Order Fagales (NOT all species produce true nuts) * Family Fagaceae * * Beech (''Fagus'') * * Chestnut (''Castanea'') * * Oak (''Quercus'') * * Stone-oak (''Lithocarpus'') * * Tanoak (''Notholithocarpus'') * Family Betulaceae * * Hazel, Filbert (''Corylus'') * * Hornbeam (''Carpinus'') A small nut may be called a nutlet. In botany, this term specifically refers to a pyrena or pyrene, which is a seed covered by a stony layer, such as the kernel of a drupe. Walnuts and hickories (Juglandaceae) have fruits that are difficult to classify. They are considered to be nuts under some definitions, but are also referred to as drupaceous nuts. "Tryma" is a specialized term for hickory fruits. In common use, a "tree nut" is, as the name implies, any nut coming from a tree. This most often comes up regarding allergies, where some people are allergic specifically to peanuts, others to a wider range of nuts that grow in trees. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Nut (fruit)」の詳細全文を読む スポンサード リンク
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