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{{About|nuts in botany|foods called nuts, which may not be true botanical nuts|Nut (food)|other kinds of nut|Nut (disambiguation)}}{{Short description|Fruit with outer shell protecting kernel}}
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A '''nut''' is a [[fruit]] consisting of a hard or tough [[nutshell]] protecting a kernel which is usually edible. In general usage and in a culinary sense, many dry [[seed]]s are called nuts, but in a botanical context, "nut" implies that the shell does not open to release the [[seed]] ([[Dehiscence (botany)|indehiscent]]).<ref>{{cite web |url=https://www.britannica.com/science/nut-plant-reproductive-body |title=Nut: Plant reproductive body |publisher=Encyclopedia Britannica |date=6 June 2024 |access-date=1 July 2024}}</ref>

Most seeds come from fruits that naturally free themselves from the shell, but this is not the case in nuts such as [[hazelnut]]s, [[chestnut]]s, and [[acorn]]s, which have hard shell walls and originate from a compound ovary.<ref name="tree_nuts_composition_phytochemicals_and_health_effects">{{Cite book |last1=Alasalvar |first1=Cesarettin |last2=Shahidi |first2=Fereidoon |title=Tree Nuts: Composition, Phytochemicals, and Health Effects (Nutraceutical Science and Technology) |date=17 December 2008 |publisher=CRC |isbn=978-0-8493-3735-2 |page=143}}</ref> 

== Definition ==
[[File:Caov2 002 phd.jpg|thumb|alt=black and white cross-section drawing of a shagbark hickory nut|Diagram of a shagbark hickory nut]]
A seed is the mature fertilised [[ovule]] of a plant; it consists of three parts, the [[embryo]] which will develop into a new plant, stored food for the embryo, and a protective seed coat. [[Botany|Botanically]], a nut is a fruit with a woody [[pericarp]] developing from a [[gynoecium#Types |syncarpous]] [[gynoecium]]. Nuts may be contained in an [[Bract#Involucral bracts|involucre]], a cup-shaped structure formed from the flower [[bract]]s. The involucre may be scaly, spiny, leafy or tubular, depending on the species of nut.<ref name=Palomar>{{cite web |url=https://www2.palomar.edu/users/warmstrong/ecoph8.htm |title=Fruits Called Nuts |author=Armstrong, W.P. |date=15 March 2009 |publisher=Palomar College |access-date=28 June 2021 |archive-date=7 November 2021 |archive-url=https://web.archive.org/web/20211107151123/https://www2.palomar.edu/users/warmstrong/ecoph8.htm |url-status=live}}</ref> Most nuts come from the [[carpel|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 (biology)|order]] [[Fagales]]. These include [[beech]] (''Fagus''), [[chestnut]] (''Castanea''), [[oak]] (''Quercus''), [[Lithocarpus|stone-oak]] (''Lithocarpus'') and [[Notholithocarpus|tanoak]] (''Notholithocarpus'') in the family [[Fagaceae]], as well as [[hazel]], [[Corylus maxima|filbert]] (''Corylus'') and [[hornbeam]] (''Carpinus'') in the family [[Betulaceae]].

A small nut may be called a "nutlet" (formerly called a nucule,<ref name=nucule>E.g., {{Citation |last=Lindley |first=John |author-link=John Lindley |title=The Vegetable Kingdom |publisher=Bradbury and Evans |date=1846 |location=London |pages=66 |url=https://books.google.com/books?id=ybw9AAAAYAAJ}}; compare {{cite web |url=https://www.wildflowers-and-weeds.com/Plant_Families/Verbenaceae.htm |title=Verbenaceae: Plants of the Verbena Family |last=Elpel |first=Thomas J. |date=1997–2021 |website=Wildflowers-and-Weeds.com |access-date=28 April 2024}} The term ''nucula'' was applied specifically to hazelnuts (''Corylus'') in {{cite book |last=Watson |first=P. W. |author-link=Peter William Watson |title=Dendrologia Britannica |publisher=Author |date=1825 |location=London |pages=xlix |url=https://books.google.com/books?id=J2Q-AAAAcAAJ}}</ref> a term otherwise referring to the [[oogonium]] of [[Charales|stoneworts]]<ref name=stonewort>{{cite book |last=Lindley |first=John |author-link=John Lindley |title=An Introduction to the Natural System of Botany |publisher=G & C & H Carvill |date=1831 |location=New York |pages=323 |url=https://books.google.com/books?id=Q2QaAAAAYAAJ}}</ref>). In [[botany]], the term "nutlet" can be used to describe a [[pyrena]] or pyrene, which is a [[seed]] covered by a stony layer, such as the kernel of a [[drupe]].<ref name=pyrena>{{cite web |url=https://www.mobot.org/mobot/latindict/keyDetail.aspx?keyWord=drupe |title=A Grammatical Dictionary of Botanical Latin s.v. Drupe |last=Eckel |first=P. M. |date=2010–2023 |publisher=Missouri Botanical Garden |access-date=28 April 2024}}</ref> 
Walnuts and [[hickory|hickories]], including [[pecans]], ([[Juglandaceae]]) have fruits that are difficult to classify. They are considered to be nuts under some definitions but are also referred to as [[Drupe|drupaceous]] nuts.<ref name="Palomar" />

==Evolutionary history==
{{Empty section|date=January 2025}}

== Toxicity ==
{{See also|Tree nut allergy}}
Nuts used for food are a common source of food allergens.<ref name="lpi">{{cite web |title=Nuts |publisher=Micronutrient Information Center, Linus Pauling Institute, Oregon State University, Corvallis, OR |date=1 September 2018 |url=https://lpi.oregonstate.edu/mic/food-beverages/nuts |access-date=28 March 2019 |archive-date=28 March 2019 |archive-url=https://web.archive.org/web/20190328191713/https://lpi.oregonstate.edu/mic/food-beverages/nuts |url-status=live}}</ref> Reactions can range from mild symptoms to severe ones, a condition known as [[anaphylaxis]], which can be life-threatening. The reaction is due to the release of [[histamine]] by the body in response to an [[allergen]] in the nuts, causing [[Food allergy#Signs and symptoms|skin and other possible reactions]].<ref>{{cite web |author=Harding, Mary |title=Nut Allergy |url=https://patient.info/allergies-blood-immune/food-allergy-and-intolerance/nut-allergy |url-status=live |archive-url=https://web.archive.org/web/20220130123419/https://patient.info/allergies-blood-immune/food-allergy-and-intolerance/nut-allergy |archive-date=30 January 2022 |access-date=10 July 2021 |publisher=Patient}}</ref> Tree nut allergies are distinct from [[peanut allergy]], as [[peanut]]s are [[legumes]], whereas a tree nut is a hard-shelled nut; however, experts suggest that a person with an allergy to peanuts should avoid eating tree nuts, and vice versa.<ref name="lpi" /><ref>{{cite web |title=Common Food Allergens |url=http://www.foodallergy.org/allergens/index.html |url-status=dead |archive-url=https://web.archive.org/web/20070613040928/http://www.foodallergy.org/allergens/index.html |archive-date=13 June 2007 |access-date=24 June 2007 |publisher=[[Food Allergy Research & Education]]}}</ref>

== Consumption as food ==
{{Main|Nut (food)}}
[[File:Chokoladekage med hasselnødder (4926078547).jpg|thumb|Chocolate cake with hazelnuts]]Nuts contain the diverse nutrients that are needed for the growth of a new plant.<ref name="lpi" /> Composition varies, but they tend to have a low water and [[carbohydrate]] content, with high levels of fats, [[protein (nutrient)|protein]], [[dietary minerals]], and [[vitamin]]s.<ref name="lpi" /> 

[[File:Très serré.jpg|thumb|An [[Eastern chipmunk]] (''Tamias striatus'') with a hazelnut in its mouth]]Nuts are eaten by humans and wildlife.<ref name="lpi" /> Because nuts generally have a high oil content, they are a significant energy source.<ref name="lpi" /> Many seeds are edible by humans and used in cooking, eaten raw, sprouted, or roasted as a [[Snack|snack food]], soaked in water and filtered to make [[Plant milk|nut milk]], ground to make nut butters, or pressed for oil that is used in cooking and cosmetics.<ref name="lpi" />

===Constituents===
Nuts are the source of energy and nutrients for the new plant. They contain a relatively large quantity of calories, essential [[Unsaturated fat|unsaturated]] and [[monounsaturated fat]]s including [[linoleic acid]] and [[linolenic acid]], vitamins, and essential amino acids.<ref name=lpi/>

==See also==
{{columnslist|colwidth=30|
* [[Nut (food)]]
* [[List of culinary nuts]]
* [[List of edible seeds]]
* [[Nutmeg]]
* [[Nutcracker]]
* [[Achene]]
}}

==References==
{{reflist|30em}}

== Further reading ==
* Albala, Ken (2014) ''Nuts A Global History''. The Edible Series. {{ISBN|978-1-78023-282-9}}

{{Nuts}}
{{Fruits}}
{{Non-timber forest products}}
{{Authority control}}

[[Category:Fruit morphology]]
[[Category:Edible nuts and seeds| ]]