Onion#Spanish Onions

The onion plant (Allium cepa), also known as the bulb onion{{GRIN |Allium cepa var. cepa |409114 |access-date=10 December 2017}} or common onion,{{sfn|Fritsch|2002|pp=9–10}} is the most widely cultivated species of the genus Allium.Eric Block, "Garlic and Other Alliums: The Lore and the Science" (Cambridge: Royal Society of Chemistry, 2010){{cite book |last=Brewster |first=James L. |title=Onions and other vegetable Alliums |edition=1st |year=1994 |publisher=CAB International |location=Wallingford, UK |isbn=978-0-85198-753-8 |page=16}} It was first officially described by Carl Linnaeus in his 1753 work Species Plantarum.{{cite book |last=Linnaeus |first=Carl |author-link= |url=https://www.biodiversitylibrary.org/page/358281 |title=Species Plantarum |publisher=Laurentii Salvii |year=1753 |volume=1 |location=Stockholm |page=262 |language=la |access-date=21 February 2018 |archive-url=https://web.archive.org/web/20180616061629/https://www.biodiversitylibrary.org/page/358281 |archive-date=16 June 2018 |url-status=live}} Synonyms during its taxonomic history are:{{PLANTS |symbol=ALCE |taxon=Allium cepa |access-date=2013-03-31}}{{ITIS |id=42720 |taxon=Allium cepa L. |access-date=2013-04-01}}

• Allium cepa var. aggregatum – G. Don
• Allium cepa var. bulbiferum – Regel
• Allium cepa var. cepa – Linnaeus
• Allium cepa var. multiplicans – L.H. Bailey
• Allium cepa var. proliferum – (Moench) Regel
• Allium cepa var. solaninum – Alef
• Allium cepa var. viviparum – (Metz) Mansf.

A. cepa is known exclusively from cultivation,{{eFloras|1|200027457|Allium cepa |first1=Dale W. Jr. |last1=McNeal |first2=T. D. |last2=Jacobsen |volume=26}} but related wild species occur in Central Asia and Iran. The most closely related include A. vavilovii from Turkmenistan and A. asarense from Iran.Grubben, G.J.H.; Denton, O.A. (2004) Plant Resources of Tropical Africa 2. Vegetables. PROTA Foundation, Wageningen; Backhuys, Leiden; CTA, Wageningen.{{cite book |last1=Zohary |first1=Daniel |last2=Hopf |first2=Maria |title=Domestication of plants in the Old World |edition=Third |location=Oxford |publisher=Oxford University Press |year=2000 |page=198 |isbn=978-0-19-850357-6}} The genus Allium contains other species variously called onions and cultivated for food, such as the Japanese bunching onion (A. fistulosum), Egyptian onion (A.  × proliferum), and Canada onion (A. canadense).{{sfn|Fritsch|2002|pp=9–10}} The vast majority of cultivars of A. cepa belong to the common onion group (A. cepa var. cepa) and are usually referred to simply as onions. The Aggregatum Group of cultivars (A. cepa var. aggregatum) includes both shallots,{{sfn|Fritsch|2002|pp=20–21}} formerly classed as a separate species,{{GRIN |access-date=2010-08-20}}{{sfn|Fritsch|2002|p=21}} and potato onions.{{sfn|Fritsch|2002|pp=20–21}} Related species include garlic, leek, and chives.{{cite book |last=Block |first=E. |title=Garlic and Other Alliums: The Lore and the Science |url=https://books.google.com/books?id=6AB89RHV9ucC |publisher=Royal Society of Chemistry |year=2010 |isbn=978-0-85404-190-9 |access-date=30 June 2020 |archive-date=1 August 2020 |archive-url=https://web.archive.org/web/20200801202704/https://books.google.com/books?id=6AB89RHV9ucC |url-status=live }}

Cepa is commonly accepted as Latin for "onion"; the generic name Allium is the classical Latin name for garlic.{{Cite web |title=Allium cepa - Plant Finder |url=https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=282056 |access-date=2024-10-06 |website=www.missouribotanicalgarden.org}}

It has an affinity with Spanish: cebolla, Italian: cipolla, Polish: cebula, and the German Zwiebel (this last altered by folk etymology). The English word "chive" is from the Old French chive , in turn from cepa.{{cite web |title=chive (n.) |url=https://www.etymonline.com/word/onion |website=Online Etymological Dictionary |access-date=8 October 2024}}

The onion is a biennial plant but is usually grown as an annual. Modern varieties typically grow to a height of {{convert|15|to|45|cm|0|abbr=on}}. The leaves are yellowish- to bluish green and grow alternately in a flattened, fan-shaped swathe. They are fleshy, hollow, and cylindrical, with one flattened side. They are at their broadest about a quarter of the way up, beyond which they taper to blunt tips. The base of each leaf is a flattened, usually white sheath that grows out of the basal plate of a bulb. From the underside of the plate, a bundle of fibrous roots extends for a short way into the soil. As the onion matures, food reserves accumulate in the leaf bases, and the bulb of the onion swells.

In the autumn, the leaves die back, and the outer scales of the bulb become dry and brittle, so the crop is normally harvested. If left in the soil over winter, the growing point in the middle of the bulb begins to develop in the spring. New leaves appear, and a long, stout, hollow stem expands, topped by a bract protecting a developing inflorescence. The inflorescence takes the form of a rounded umbel of white flowers with parts in sixes. The seeds are glossy black and triangular in cross-section. The average pH of an onion is around 5.5.{{Cite web |url=https://foodsafety.wisc.edu/business_food/files/Approximate_pH.pdf |title=Approximate pH Values of Common Foods and Ingredients |website=Wisconsin Food Safety and Health |archive-url=https://web.archive.org/web/20121224184605/http://www.foodsafety.wisc.edu/business_food/files/Approximate_pH.pdf |archive-date=2012-12-24 |url-status=dead |access-date=8 January 2018}}

File:ARS red onion.jpg|Roots, leaves and developing bulb

File:Onion Flower Bangladesh.jpg|Inflorescence with flower buds

File:Onion seed.jpg|Seeds

File:An onion, woodcut, 1547 Wellcome L0029214.jpg (1547)]]

Humans have grown and selectively bred onions in cultivation for at least 7,000 years.{{cite book |last=Anastassakis |first=Konstantinos |chapter=Allium Cepa (Red Onion) |date=2022 |title=Androgenetic Alopecia From A to Z |pages=465–469 |chapter-url=https://link.springer.com/10.1007/978-3-031-08057-9_54 |access-date=2024-06-06 |place=Cham |publisher=Springer International Publishing |doi=10.1007/978-3-031-08057-9_54 |isbn=978-3-031-08056-2}} The geographic origin of the onion is uncertain; ancient records of onion use span both eastern and western Asia.{{Cite book |url=https://books.google.com/books?id=WqfACQAAQBAJ&pg=PA248 |title=Onion. In: Foods that Changed History: How Foods Shaped Civilization from the Ancient World to the Present |last=Cumo |first=C.E. |publisher=ABC-CLIO LLC (American Bibliographic Center, CLIO Press) |year=2015 |pages=248–250 |isbn=9781440835377 |access-date=30 June 2020 |archive-date=4 February 2021 |archive-url=https://web.archive.org/web/20210204030543/https://books.google.com/books?id=WqfACQAAQBAJ&pg=PA248 |url-status=live }}{{Cite journal |last=Ansari |first=Naser Alemzadeh |year=2007 |title=Onion Cultivation and Production in Iran |url=http://www.globalsciencebooks.info/Online/GSBOnline/images/0712/MERJPSB_1(1&2)/MERJPSB_1(2)26-38o.pdf |journal=Middle Eastern and Russian Journal of Plant Science and Biotechnology |volume=1 |issue=2 |pages=26–38 |quote=Onion originated in Iran and its neighboring countries (Hanelt 1990). |via=Global Science Books |access-date=22 April 2022 |archive-date=28 August 2021 |archive-url=https://web.archive.org/web/20210828162151/http://www.globalsciencebooks.info/Online/GSBOnline/images/0712/MERJPSB_1%281%262%29/MERJPSB_1%282%2926-38o.pdf |url-status=live }} Domestication likely took place in West or Central Asia.{{sfn|Fritsch|2002|pp=20–21}}{{cite web |url=https://www.onions-usa.org/all-about-onions/history-of-onions |title=History of onions |publisher=US National Onion Association, Greeley, CO |date=2011 |access-date=23 January 2017 |archive-date=24 June 2017 |archive-url=https://web.archive.org/web/20170624120840/https://www.onions-usa.org/all-about-onions/history-of-onions |url-status=live }} Onions have been variously described as having originated in Iran, western Pakistan and Central Asia.{{r|NOA|p=1|quote=Many archaeologists, botanists, and food historians believe onions originated in central Asia. Other research suggests onions were first grown in Iran and West Pakistan.}}{{Cite book |url=https://books.google.com/books?id=6AB89RHV9ucC |title=Garlic and Other Alliums: The Lore and the Science |last=Block |first=Eric |date=2010 |publisher=Royal Society of Chemistry |isbn=9780854041909 |pages=5–6 |access-date=30 June 2020 |archive-date=1 August 2020 |archive-url=https://web.archive.org/web/20200801202704/https://books.google.com/books?id=6AB89RHV9ucC |url-status=live }} The onion species Allium fistulosum (spring onion, bunching onion) and Allium tuberosum (Chinese leek) were domesticated in China around 6000 BC alongside other vegetables, grains, and fruits.{{cite book |last1=Veeck |first1=Gregory |last2=Pannell |first2=Clifton W. |title=China's Geography |publisher=Rowman & Littlefield |location=Lanham, Boulder, New York, London |isbn=9781538140796 |page=235 |edition=4th |chapter=9. Agriculture: From Antiquity to Revolution to Reform. Early Farming Traditions|date=2021 }}

Recipes using onions and other Allium species were recorded in cuneiform script on clay tablets in ancient Mesopotamia, around 2000 BC; the tablets are held in Yale University's Babylonian collection. The Assyriologist and "gourmet cook" Jean Bottero stated this was "a cuisine of striking richness, refinement, sophistication and artistry".{{cite web |title=Three cheers for the onion |url=https://www.bbc.co.uk/news/magazine-30549150 |publisher=BBC |access-date=14 October 2024 |date=4 January 2015}}

Ancient Egyptians revered the onion bulb, viewing its spherical shape and concentric rings as symbols of eternal life. Onions were used in Egyptian burials, as evidenced by onion traces found in the eye sockets of Ramesses IV.{{cite journal |author1=Abdel-Maksouda, Gomaa |author2=El-Aminb, Abdel-Rahman |year=2011 |title=A review on the materials used during the mummification process in ancient Egypt |journal=Mediterranean Archaeology and Archaeometry |volume=11 |issue=2 |pages=129–150 |url=http://www.maajournal.com/Issues/2011/pdf/Maksoud.pdf |access-date=13 September 2013 |archive-date=8 March 2014 |archive-url=https://web.archive.org/web/20140308070536/http://www.maajournal.com/Issues/2011/pdf/Maksoud.pdf |url-status=live }} Pliny the Elder of the first century AD wrote about the use of onions and cabbage in Pompeii. He documented Roman beliefs about the onion's ability to improve ocular ailments, aid in sleep, and heal everything from oral sores and toothaches to dog bites, lumbago, and even dysentery. Archaeologists unearthing Pompeii long after its 79 AD volcanic burial have found gardens resembling those in Pliny's detailed narratives. According to texts collected in the fifth/sixth century AD under the authorial aegis of "Apicius" (said to have been a gourmet), onions were used in many Roman recipes.

In the Age of Discovery, onions were taken to North America by the first European settlers in part of the Columbian exchange. They found close relatives of the plant such as Allium tricoccum readily available and widely used in Native American gastronomy. According to diaries kept by some of the first English colonists, the bulb onion was one of the first crops planted in North America by the Pilgrim fathers. Between 1883 and 1939, inventors in the United States patented 97 inventions meant to make onion-growing more efficient through automation.{{cite journal |last1=Gripshover |first1=Margaret M. |first2=Thomas L. |last2=Bell |title=Patently Good Ideas: Innovations and Inventions in U.S. Onion Farming, 1883–1939 |journal=Material Culture |date=Spring 2012 |volume=44 |issue=1 |pages=1–30 |jstor=23145818}}

{{See also|List of onion dishes}}

File:Frying onion.JPG onions]]

Three colour varieties of onions offer different possibilities for the cook:

• Yellow or brown onions are sweet, with many cultivars bred specifically to accentuate this sweetness, such as Vidalia, Walla Walla, Cévennes, and Bermuda.{{cite web |last=Oulton |first=Randal |url=http://www.cooksinfo.com/bermuda-onions |title=Bermuda Onions|date=2005-09-09 |website=cooksinfo.com |access-date=2017-11-25 |archive-date=11 February 2021 |archive-url=https://web.archive.org/web/20210211230456/https://www.cooksinfo.com/bermuda-onions |url-status=live }} Yellow onions turn a rich, dark brown when caramelised and are used to add a sweet flavour to various dishes, such as French onion soup.{{cite web |url=http://thecookingdish.com/0330/the-difference-between-yellow-onions-white-onions-and-red-onions/ |title=The Difference between Yellow, White, and Red Onions |last=Mower |first=Chris |website=The Cooking Dish |date=30 March 2009 |access-date=2013-03-24 |archive-date=1 May 2013 |archive-url=https://web.archive.org/web/20130501192552/http://thecookingdish.com/0330/the-difference-between-yellow-onions-white-onions-and-red-onions/ |url-status=live }}
• Red or purple onions, known for their sharp pungent flavour, are commonly cooked in many cuisines, and used raw and in grilling.
• White onions are mild in flavour; they have a golden colour when cooked and a particularly sweet flavour when sautéed.

While the large, mature onion bulb is most often eaten, onions can be eaten at immature stages. Young plants may be harvested before bulbing occurs and used whole as spring onions or scallions. When an onion is harvested after bulbing has begun, but the onion is not yet mature, the plants are sometimes referred to as "summer" onions. Onions may be bred and grown to mature at smaller sizes, known as pearl, boiler, or pickler onions; these are not true pearl onions which are a different species.{{cite book |last=Thompson |first=Sylvia |year=1995 |title=The Kitchen Garden |publisher=Bantam Books |page=143}} Pearl and boiler onions may be cooked as a vegetable rather than as an ingredient, while pickler onions are often preserved in vinegar as a long-lasting relish.{{cite book |title=Home Preservation of Fruit and Vegetables |author1=Ministry of Agriculture |author2=Fisheries and Food |year=1968 |publisher=HMSO |page=107}} Onions pickled in vinegar are eaten as a side serving with traditional pub food such as a ploughman's lunch.{{cite web |title=Traditional English Pub Style Ploughman's Lunch |url=https://www.food.com/recipe/traditional-english-pub-style-ploughmans-lunch-250126 |website=Food.com |access-date=8 October 2024}}

Onions are commonly chopped and used as an ingredient in various hearty warm dishes, and may be used as a main ingredient in their own right, for example in French onion soup, creamed onions, and onion chutney. They are versatile and can be baked, boiled, braised, grilled, fried, roasted, sautéed, or eaten raw in salads.{{cite web |url=http://www.bbcgoodfood.com/content/knowhow/glossary/onion/ |title=Onion |website=GoodFood |publisher=BBC |access-date=2013-04-02 |archive-date=30 May 2013 |archive-url=https://web.archive.org/web/20130530032911/http://www.bbcgoodfood.com/content/knowhow/glossary/onion/ |url-status=live }} Onions are a major ingredient of some curries; the Persian-style dopiaza's name means "double onion", and it is used both in the dish's sour curry sauce and as a garnish.{{cite web |last=Dillon |first=Sheila |author-link=Sheila Dillon |title=From balti to bhuna: the ultimate guide to curry |url=https://www.bbc.co.uk/programmes/articles/3jPY8xvk41DrT93Lw4XPk1w/from-balti-to-bhuna-the-ultimate-guide-to-curry |publisher=BBC Radio 4 |access-date=7 October 2024 |date=2024}} Onion powder is a seasoning made from finely ground, dehydrated onions; it is often included in seasoned salt and spice mixes.{{cite book |last=Engineers |first=N.B.C. |title=The Complete Book on Onion & Garlic Cultivation with Processing (Production of Onion Paste, Flakes, Powder & Garlic Paste, Powder, Flakes, Oil) |year=2015 |isbn=978-81-7833-159-1 |url=https://books.google.com/books?id=WchbCgAAQBAJ&pg=PA169 |pages=169–175 |publisher=Asia Pacific Business Press}}

File:Cells from a red onion epidermal peel.tif cells are visible in true color with minimal magnification.]]

Onions have particularly large cells that are easy to observe under low magnification. Forming a single layer of cells, the bulb epidermis is easy to separate for educational, experimental, and breeding purposes.{{Cite journal |pmid=19684107 |year=2009 |last1=Suslov |first1=D |title=Onion epidermis as a new model to study the control of growth anisotropy in higher plants |journal=Journal of Experimental Botany |volume=60 |issue=14 |pages=4175–4187 |last2=Verbelen |first2=J. P. |last3=Vissenberg |first3=K. |doi=10.1093/jxb/erp251|doi-access=free}}{{Cite journal |pmid=24416168 |year=2014 |last1=Xu |first1=K |title=A rapid, highly efficient and economical method of Agrobacterium-mediated in planta transient transformation in living onion epidermis |journal=PLOS ONE |volume=9 |issue=1 |page=e83556 |last2=Huang |first2=X. |last3=Wu |first3=M. |last4=Wang |first4=Y |last5=Chang |first5=Y |last6=Liu |first6=K |last7=Zhang |first7=J |last8=Zhang |first8=Y. |last9=Zhang |first9=F. |last10=Yi |first10=L |last11=Li |first11=T. |last12=Wang |first12=R. |last13=Tan |first13=G. |last14=Li |first14=C. |display-authors=5 |doi=10.1371/journal.pone.0083556 |pmc=3885512 |bibcode=2014PLoSO...983556X |doi-access=free}} Onions are therefore commonly used in science education to teach the use of a microscope for observing cell structure.{{cite book |author1=Anne McCabe |author2=Mick O'Donnell |author3=Rachel Whittaker |title=Advances in Language and Education |url=https://books.google.com/books?id=UKLc_kfOJb8C&pg=PA35 |date=19 July 2007 |publisher=Bloomsbury Publishing |isbn=978-1-4411-0458-8 |page=35 |access-date=2 August 2015 |archive-date=26 September 2015 |archive-url=https://web.archive.org/web/20150926023847/https://books.google.com/books?id=UKLc_kfOJb8C&pg=PA35 |url-status=live }} Onion skins can be boiled to make an orange-brown dye.{{cite web |url=http://www.allnaturaldyeing.com/onion-skin-dye/ |website=All Natural Dyeing |title=Onion Skin Dye (Yellow and Purple) |access-date=31 July 2020 |archive-date=6 August 2020 |archive-url=https://web.archive.org/web/20200806051713/http://www.allnaturaldyeing.com/onion-skin-dye/ |url-status=live }}

{{nutritional value |name=Raw onion bulbs

|water=89.11 g

|kJ=166

|protein=1.1 g

|fat=0.1 g

|carbs=9.34 g

|fibre=1.7 g

|sugars=4.24 g

|calcium_mg=23

|iron_mg=0.21

|magnesium_mg=10

|phosphorus_mg=29

|potassium_mg=146

|zinc_mg=0.17

|manganese_mg=0.129

|vitC_mg=7.4

|thiamin_mg=0.046

|riboflavin_mg=0.027

|niacin_mg=0.116

|pantothenic_mg=0.123

|vitB6_mg=0.12

|folate_ug=19

|opt1n=Fluoride

|opt1v=1.1 µg

|source_usda=1

|note=[https://fdc.nal.usda.gov/fdc-app.html#/food-details/170000/nutrients Link to USDA Database entry]

}}

Most onion cultivars are about 89% water, 9% carbohydrates (including 4% sugar and 2% dietary fibre), 1% protein, and negligible fat (table). Onions contain low amounts of essential nutrients and have an energy value of 166 kJ (40 kilocalories) in a 100 g (3.5 oz) amount. Onions contribute savoury flavour to dishes without contributing significant caloric content.

Onion varieties vary widely in phytochemical content, particularly for polyphenols, with shallots having the highest level, six times the amount found in Vidalia onions. Yellow onions have the highest total flavonoid content, an amount 11 times higher than in white onions. Red onions have considerable content of anthocyanin pigments, with at least 25 different compounds identified representing 10% of total flavonoid content. Like garlic,{{Cite journal |last=Lukes |first=T. M. |date=1986-11-01 |title=Factors Governing the Greening of Garlic Puree |journal=Journal of Food Science |volume=51 |issue=6 |page=1577 |doi=10.1111/j.1365-2621.1986.tb13869.x}} onions can show an additional colour – pink-red – after cutting, an effect caused by reactions of amino acids with sulfur compounds.{{Cite journal |last1=Lee |first1=Eun Jin |last2=Rezenom |first2=Yohannes H. |last3=Russell |first3=David H. |last4=Patil |first4=Bhimanagouda S. |last5=Yoo |first5=Kil Sun |date=2012-04-01 |title=Elucidation of chemical structures of pink-red pigments responsible for 'pinking' in macerated onion (Allium cepa L.) using HPLC–DAD and tandem mass spectrometry |journal=Food Chemistry |volume=131 |issue=3 |pages=852–861 |doi=10.1016/j.foodchem.2011.09.059}} Onion polyphenols are under basic research to determine their possible biological properties in humans.{{Cite journal |pmid=17997520 |year=2007 |last1=Slimestad |first1=R. |last2=Fossen |first2=T. |last3=Vågen |first3=I. M. |title=Onions: A source of unique dietary flavonoids |journal=Journal of Agricultural and Food Chemistry |volume=55 |issue=25 |pages=10067–10080 |doi=10.1021/jf0712503|bibcode=2007JAFC...5510067S }}{{cite journal |last1=Olsson |first1=M.E. |last2=Gustavsson |first2=K.E. |last3=Vågen |first3=I.M. |name-list-style=amp |year=2010 |title=Quercetin and isorhamnetin in sweet and red cultivars of onion (Allium cepa L.) at harvest, after field curing, heat treatment, and storage |journal=Journal of Agricultural and Food Chemistry |volume=58 |issue=4 |pages=2323–2330 |doi=10.1021/jf9027014 |pmid=20099844|bibcode=2010JAFC...58.2323O }}

Some people suffer from allergic reactions after handling onions.{{cite journal |last1=Cantisani |first1=C. |last2=Visconti |first2=B. |last3=Paolino |first3=G. |last4=Frascani |first4=F. |last5=Tofani |first5=S. |last6=Fazia |first6=G. |last7=Calvieri |first7=S. |title=Unusual food allergy: Alioidea allergic reactions overview |journal=Recent Patents on Inflammation & Allergy Drug Discovery |volume=8 |issue=3 |pages=178–84 |doi=10.2174/1872213X08666141107170159 |pmid=25381903 |year=2014}} Symptoms can include contact dermatitis, intense itching, rhinoconjunctivitis, blurred vision, bronchial asthma, sweating, and anaphylaxis. Allergic reactions may not occur when eating cooked onions, possibly due to the denaturing of the proteins from cooking.{{cite journal |last1=Arochena |first1=L. |last2=Gámez |first2=C. |last3=del Pozo |first3=V. |last4=Fernández-Nieto |first4=M. |year=2012 |title=Cutaneous allergy at the supermarket |journal=Journal of Investigational Allergology and Clinical Immunology |volume=22 |issue=6 |pages=441–442 |pmid=23101191}}

Freshly cut onions can produce a stinging sensation in the eyes of people nearby and often uncontrollable tears. This is caused by the release of a volatile liquid, syn-propanethial-S-oxide and its aerosol, which stimulates nerves in the eye. This gas is produced by a chain of reactions which serve as a defence mechanism: chopping an onion causes damage to cells which releases enzymes called alliinases. These break down amino acid sulfoxides and generate sulfenic acids. A specific sulfenic acid, 1-propenesulfenic acid, is rapidly acted on by a second enzyme, the lacrimatory factor synthase (LFS), producing the syn-propanethial-S-oxide. This gas diffuses through the air and soon reaches the eyes, where it activates sensory neurons. Lacrimal glands produce tears to dilute and flush out the irritant. Eye irritation can be minimised by cutting onions under running water or submerged in a basin of water.{{cite web |last=Scott |first=Thomas |title=What is the chemical process that causes my eyes to tear when I peel an onion! |website=Ask the Experts: Chemistry |publisher=Scientific American |url=http://www.sciam.com/article.cfm?id=what-is-the-chemical-proc |access-date=2007-04-28 |archive-date=22 April 2022 |archive-url=https://web.archive.org/web/20220422190206/https://www.scientificamerican.com/article/what-is-the-chemical-proc/ |url-status=live }} Leaving the root end intact also reduces irritation as the onion base has a higher concentration of sulphur compounds than the rest of the bulb.{{cite web |url=http://www.onions-usa.org/about/faq.php#cooking |title=FAQ |publisher=National Onion Association |access-date=2013-03-28 |archive-url=https://web.archive.org/web/20110318030002/http://www.onions-usa.org/about/faq.php#cooking |archive-date=18 March 2011 |url-status=dead}}

File:Cortando cebolla.jpg|Cut onions emit a chemical compound which cause the lacrimal glands in the eyes to become irritated, releasing tears.

File:Syn-propanethial-S-oxide-3D-balls.png|Model of syn-Propanethial-S-oxide, the volatile molecule that causes eye irritation

The amount of sulfenic acids and lacrimal factor released and the irritation effect differs among Allium species. In 2008, the New Zealand Institute for Crop and Food Research created "no tears" onions by genetic modification to prevent the synthesis of lachrymatory factor synthase in onions.{{cite web |url=https://www.sciencedaily.com/releases/2008/02/080202115345.htm |title=Tearless Onion Created in Lab Using Gene Silencing |website=ScienceDaily |date=5 February 2008 |access-date=23 November 2016 |archive-date=24 November 2016 |archive-url=https://web.archive.org/web/20161124025149/https://www.sciencedaily.com/releases/2008/02/080202115345.htm |url-status=live }} One study suggests that consumers prefer the flavour of onions with lower LFS content.{{Cite journal |last1=Kim |first1=Ha-Yeon |last2=Jackson |first2=Daniel |last3=Adhikari |first3=Koushik |last4=Riner |first4=Cliff |last5=Sanchez-Brambila |first5=Gabriela |date=2017-10-01 |title=Relationship Between Consumer Acceptability and Pungency-Related Flavor Compounds of Vidalia Onions |journal=Journal of Food Science |volume=82 |issue=10 |pages=2396–2402 |doi=10.1111/1750-3841.13915 |pmid=28898424}} Since the process impedes sulfur ingestion by the plant, some find LFS− onions inferior in flavour.{{Cite journal |last1=Eady |first1=Colin C. |last2=Kamoi |first2=Takahiro |last3=Kato |first3=Masahiro |last4=Porter |first4=Noel G. |last5=Davis |first5=Sheree |last6=Shaw |first6=Martin |last7=Kamoi |first7=Akiko |last8=Imai |first8=Shinsuke |date=2008-08-01 |title=Silencing Onion Lachrymatory Factor Synthase Causes a Significant Change in the Sulfur Secondary Metabolite Profile |journal=Plant Physiology |volume=147 |issue=4 |pages=2096–2106 |doi=10.1104/pp.108.123273 |pmid=18583530 |pmc=2492635}}

A method for efficiently differentiating LFS− and LFS+ onions has been developed based on mass spectrometry, with potential application in high-volume production;{{Cite journal |last1=Joyce |first1=Nigel I. |last2=Eady |first2=Colin C. |last3=Silcock |first3=Patrick |last4=Perry |first4=Nigel B. |last5=van Klink |first5=John W. |date=January 2013 |title=Fast Phenotyping of LFS-Silenced (Tearless) Onions by Desorption Electrospray Ionization Mass Spectrometry (DESI-MS) |journal=Journal of Agricultural and Food Chemistry |volume=61 |issue=7 |pages=1449–1456 |doi=10.1021/jf304444s |pmid=23350988|bibcode=2013JAFC...61.1449J }} gas chromatography is also used to measure lachrymatory factor in onions.{{Cite journal |last1=Tewari |first1=Gyanendra M. |last2=Bandyopadhyay |first2=Chiranjib. |date=1975-07-01 |title=Quantitative evaluation of lachrymatory factor in onion by thin-layer chromatography |journal=Journal of Agricultural and Food Chemistry |volume=23 |issue=4 |pages=645–647 |doi=10.1021/jf60200a0441|doi-broken-date=1 November 2024 }}{{Cite journal |last1=Schmidt |first1=Norman E. |last2=Santiago |first2=Leanne M. |last3=Eason |first3=H. Donald |last4=Dafford |first4=Kurtus A. |last5=Grooms |first5=Chris A. |last6=Link |first6=Tammy E. |last7=Manning |first7=Dana T. |last8=Cooper |first8=Sylina D. |last9=Keith |first9=R. Chad |date=1996-01-01 |title=Rapid Extraction Method of Quantitating the Lachrymatory Factor of Onion Using Gas Chromatography |journal=Journal of Agricultural and Food Chemistry |volume=44 |issue=9 |pages=2690–2693 |doi=10.1021/jf950686s|bibcode=1996JAFC...44.2690S }} In early 2018, Bayer released the first crop yield of commercially available LFS-silenced onions under the name "Sunions".{{Cite news |url=https://www.npr.org/sections/thesalt/2018/02/08/583703262/stop-crying-tear-free-onions-are-here |title=Stop Crying! Tear-Free Onions Are Here |last=Danovich |first=Tove |date=8 February 2018 |publisher=NPR |access-date=13 April 2018 |archive-date=17 April 2018 |archive-url=https://web.archive.org/web/20180417025118/https://www.npr.org/sections/thesalt/2018/02/08/583703262/stop-crying-tear-free-onions-are-here |url-status=live }} They were the product of 30 years of cross-breeding; genetic modification was not employed.{{Cite news |url=http://www.latimes.com/food/sns-dailymeal-1863539-healthy-eating-tearless-onions-121917-20171219-story.html |title=Onions that don't make you cry are finally here |last=Van Hare |first=Holly |date=19 December 2017 |newspaper=Los Angeles Times |access-date=15 April 2018 |archive-date=13 April 2018 |archive-url=https://web.archive.org/web/20180413034721/http://www.latimes.com/food/sns-dailymeal-1863539-healthy-eating-tearless-onions-121917-20171219-story.html |url-status=live }}

Guinea hen weed and honey garlic contain a similar lachrymatory factor.{{Cite news |url=https://www.nytimes.com/2017/09/05/science/onions-crying-chemicals.html |title=Why Onions Make You Cry |last=Klein |first=Joanna |date=5 September 2017 |work=The New York Times |access-date=16 April 2018 |archive-date=17 April 2018 |archive-url=https://web.archive.org/web/20180417025055/https://www.nytimes.com/2017/09/05/science/onions-crying-chemicals.html |url-status=live }} Synthetic onion lachrymatory factor has been used in a study related to tear production,{{cite journal |doi=10.1007/s10384-009-0786-0 |volume=54 |title=Using synthesized onion lachrymatory factor to measure age-related decreases in reflex-tear secretion and ocular-surface sensation |year=2010 |journal=Japanese Journal of Ophthalmology |pages=215–220 |last1=Higashihara |first1=Hisayo |last2=Yokoi |first2=Norihiko |last3=Aoyagi |first3=Morihiro |last4=Tsuge |first4=Nobuaki |last5=Imai |first5=Shinsuke |last6=Kinoshita |first6=Shigeru |s2cid=23549173 |issue=3 |pmid=20577855}} and has been proposed as a nonlethal deterrent against thieves and intruders.{{Cite patent |country=US |number=9482496B1 |status=patent |title=Wall-mounted nonlethal device for defending against intruders |pubdate=2015-06-01 |gdate=2016-11-01 |pridate=2015-06-01 |inventor=James Anthony Rocchi, Thomas John Stewart |invent1=James Anthony Rocchi |invent2=Thomas John Stewart |assign1=Fighting Chance Systems Inc |url=https://patents.google.com/patent/US9482496B1/en }} {{Webarchive|url=https://web.archive.org/web/20210318041651/https://patents.google.com/patent/US9482496B1/en |date=18 March 2021 }}{{cite patent |country=US |number=9890561B2 |status=patent |title=Pressurized chemical theft deterrent device |pubdate=2017-03-03 |gdate=2018-02-13 |pridate=2016-03-04 |inventor=Yves Perrenoud, Daniel Idzkowski |invent1=Yves Perrenoud |invent2=Daniel Idzkowski |assign1=Skunklock Inc |url=https://patents.google.com/patent/US9890561B2/en }} {{Webarchive|url=https://web.archive.org/web/20200113141617/https://patents.google.com/patent/US9890561B2/en |date=13 January 2020 }}

Onions are toxic to animals including dogs, cats, and guinea pigs.{{cite journal |last1=Cope |first1=R.B. |last2=Monteiro |first2=L.N. |last3=Rocha |first3=N.S. |title=Allium species poisoning in dogs and cats |journal=Veterinary Medicine |date=August 2005 |volume=100 |issue=8 |pages=562–566 |url=https://www.aspcapro.org/sites/default/files/c-vetm0805_562-566.pdf |access-date=22 July 2022 }}{{cite journal |last=Salgado |first=B.S. |title=Allium species poisoning in dogs and cats |journal=Journal of Venomous Animals and Toxins Including Tropical Diseases |year=2011 |volume=17 |issue=1 |pages=4–11 |doi=10.1590/S1678-91992011000100002 |doi-access=free |hdl=11449/12942 |hdl-access=free }}

File:Onion mother plants (bulbs) for production seeds.jpg

File:Field with onions.jpg

Onions are best cultivated in fertile, well-drained soils. Sandy loams are good as they are low in sulphur, while clayey soils usually have a high sulphur content and produce pungent bulbs. Onions require a high level of nutrients in the soil. Phosphorus is often present in sufficient quantities, but may be applied before planting because of its low level of availability in cold soils. Nitrogen and potash can be applied at regular intervals during the growing season, the last application of nitrogen being at least four weeks before harvesting.{{cite web |url=http://www.caes.uga.edu/publications/pubDetail.cfm?pk_id=7749 |title=2007 Onion Production Guide |editor-last=Boyhan |editor-first=George E. |editor-last2=Kelley |editor-first2=W. Terry |year=2007 |website=Production Guides |publisher=University of Georgia: College of Agricultural and Environmental Sciences |access-date=2013-09-14 |archive-date=11 October 2013 |archive-url=https://web.archive.org/web/20131011180348/http://www.caes.uga.edu/Publications/pubDetail.cfm?pk_id=7749 |url-status=live }}

Bulbing onions are day-length sensitive; their bulbs begin growing only after the number of daylight hours has surpassed some minimal quantity. Most traditional European onions are referred to as "long-day" onions, producing bulbs only after 14 hours or more of daylight occurs. Southern European and North African varieties are often known as "intermediate-day" types, requiring only 12–13 hours of daylight to stimulate bulb formation. "Short-day" onions, which have been developed in more recent times, are planted in mild-winter areas in the autumn and form bulbs in the early spring and require only 11–12 hours of daylight to stimulate bulb formation.{{cite web |url=http://extension.oregonstate.edu/gardening/onion-bulb-formation-strongly-linked-day-length |title=Onion bulb formation is strongly linked with day length |last=Savonen |first=Carol |date=2006-07-13 |publisher=Oregon State University Extension Service |access-date=2013-09-14 |archive-date=9 November 2013 |archive-url=https://web.archive.org/web/20131109131226/http://extension.oregonstate.edu/gardening/onion-bulb-formation-strongly-linked-day-length |url-status=live }} Onions are a cool-weather crop and can be grown in USDA zones 3 to 9. Hot temperatures or other stressful conditions cause them to "bolt", meaning that a flower stem begins to grow.{{cite web |url=http://www.gardeningknowhow.com/edible/vegetables/onion/onion-bolting.htm |title=What is Onion Bolting and how to Keep an Onion from Bolting |last=Rhoades |first=Jackie |website=Gardening Know How |date=17 August 2010 |access-date=2013-03-27 |archive-date=1 May 2013 |archive-url=https://web.archive.org/web/20130501001809/http://www.gardeningknowhow.com/edible/vegetables/onion/onion-bolting.htm |url-status=live }}

Onions are grown from seeds or from partially grown bulbs called "sets" or starter bulbs. Onion seeds are short-lived and fresh seeds germinate more effectively when sown in shallow rows, or "drills," with each drill 12" to 18" apart.{{cite web |url=http://www.almanac.com/plant/onions |title=Onions: Planting, Growing and Harvesting Onion Plants |website=The Old Farmer's Almanac |access-date=2013-03-27 |archive-date=5 November 2012 |archive-url=https://web.archive.org/web/20121105125106/http://www.almanac.com/plant/onions |url-status=live }}{{cite web |url=http://www.ars.usda.gov/Aboutus/docs.htm?docid=6463 |title=Onion production |date=2011-02-23 |publisher=USDA: Agricultural Research Service |access-date=2013-03-27 |archive-date=11 April 2014 |archive-url=https://web.archive.org/web/20140411135334/http://www.ars.usda.gov/Aboutus/docs.htm?docid=6463 |url-status=live }} In suitable climates, certain cultivars can be sown in late summer and autumn to overwinter in the ground and produce early crops the following year.

Onion bulbs are produced by sowing seeds in a dense pattern in early summer, then harvested in the autumn when the bulbs are still small, followed by drying and storage. These bulbs are planted the following spring and grow into mature bulbs later in the growing season.{{PFAF |access-date=2013-03-22}} Certain cultivars used for growing and storing bulbs may not have as good storage characteristics as those grown directly from seed.{{cite book |title=The Royal Horticultural Society Encyclopedia of Gardening |editor-last=Brickell |editor-first=Christopher |year=1992 |publisher=Dorling Kindersley |isbn=978-0-86318-979-1 |page=345}}

Routine care during the growing season involves keeping the rows free of competing weeds, especially when the plants are young. The plants are shallow-rooted and do not need much water when established. Bulbing usually takes place after 12 to 18 weeks. The bulbs can be gathered when needed to eat fresh, but if stored, they are harvested after the leaves have died back naturally. In dry weather, they may be left on the surface of the soil for a few days for drying, then are placed in nets, roped into strings, or laid in layers in shallow boxes to be stored in a cool, well-ventilated place.

Onions suffer from several pests and diseases. The most serious for the home gardener are likely to be the onion fly, stem and bulb eelworm, white rot, and neck rot. Diseases affecting the foliage include rust and smut, downy mildew, and white tip disease. The bulbs may be affected by splitting, white rot, and neck rot. Shanking is a condition in which the central leaves turn yellow and the inner part of the bulb collapses into an unpleasant-smelling slime. Most of these disorders are best treated by removing and burning affected plants.{{cite book |title=Be your own Vegetable Doctor |last=Hessayon |first=D.G. |author-link=D. G. Hessayon |year=1978 |publisher=Pan Britannica Industries |isbn=978-0-903505-08-6 |pages=22–23}} The larvae of the onion leaf miner or leek moth (Acrolepiopsis assectella) sometimes attack the foliage and may burrow down into the bulb.{{cite journal |last=Landry |first=Jean-François |s2cid=86748199 |year=2007 |title=Taxonomic review of the leek moth genus Acrolepiopsis (Lepidoptera: Acrolepiidae) in North America |journal=The Canadian Entomologist |volume=139 |issue=3 |pages=319–353 |doi=10.4039/n06-098}}

The onion fly (Delia antiqua) lays eggs on the leaves and stems and on the ground close to onion, shallot, leek, and garlic plants. The fly is attracted to the crop by the smell of damaged tissue and is liable to occur after thinning. Plants grown from sets are less prone to attack. The larvae tunnel into the bulbs and the foliage wilts and turns yellow. The bulbs are disfigured and rot, especially in wet weather. Control measures may include crop rotation, the use of seed dressings, early sowing or planting, and the removal of infested plants.{{cite web |url=http://www.agroatlas.ru/en/content/pests/Delia_antiqua/ |title=Delia antiqua (Meigen): Onion Fly |website=Interactive Agricultural Ecological Atlas of Russia and Neighboring Countries |access-date=2013-03-29 |archive-date=14 May 2013 |archive-url=https://web.archive.org/web/20130514095654/http://www.agroatlas.ru/en/content/pests/Delia_antiqua/ |url-status=live }}

The onion eelworm (Ditylenchus dipsaci), a tiny parasitic soil-living nematode, causes swollen, distorted foliage. Young plants are killed and older ones produce soft bulbs. No cure is known and affected plants should be uprooted and burned. The site should not be used for growing onions again for several years and should also be avoided for growing carrots, parsnips, and beans, which are also susceptible to the eelworm.{{cite web |url=http://www.gardenaction.co.uk/techniques/pests/onion_eelworm.htm |title=Onion Eelworm (Ditylenchus dipsaci) |year=2011 |website=GardenAction |access-date=2013-03-29 |archive-date=3 February 2013 |archive-url=https://web.archive.org/web/20130203011252/http://www.gardenaction.co.uk/techniques/pests/onion_eelworm.htm |url-status=live }}

White rot of onions, leeks, and garlic is caused by the soil-borne fungus Sclerotium cepivorum. As the roots rot, the foliage turns yellow and wilts. The bases of the bulbs are attacked and become covered by a fluffy white mass of mycelia, which later produces small, globular black structures called sclerotia. These resting structures remain in the soil to reinfect a future crop. No cure for this fungal disease exists, so affected plants should be removed and destroyed and the ground used for unrelated crops in subsequent years.{{cite web |url=https://www.rhs.org.uk/advice/profile?pid=226 |title=Onion white rot |website=RHS Gardening |publisher=Royal Horticultural Society |access-date=2013-03-29 |archive-date=4 August 2018 |archive-url=https://web.archive.org/web/20180804231507/https://www.rhs.org.uk/advice/profile?pid=226 |url-status=live }}

Neck rot is a fungal disease affecting onions in storage. It is caused by Botrytis allii, which attacks the neck and upper parts of the bulb, causing a grey mould to develop. The symptoms often first occur where the bulb has been damaged and spread down the affected scales. Large quantities of spores are produced and crust-like sclerotia may also develop. In time, a dry rot sets in and the bulb becomes a dry, mummified structure. This disease may be present throughout the growing period, but only manifests itself when the bulb is in storage. Antifungal seed dressings are available and the disease can be minimised by preventing physical damage to the bulbs at harvesting, careful drying and curing of the mature onions, and correct storage in a cool, dry place with plenty of circulating air.{{cite web |url=https://www.rhs.org.uk/advice/profile?PID=747 |title=Onion neck rot |website=RHS Gardening |publisher=Royal Horticultural Society |access-date=2013-03-29 |archive-date=4 August 2018 |archive-url=https://web.archive.org/web/20180804231835/https://www.rhs.org.uk/advice/profile?PID=747 |url-status=live }}

File:Uienvlieg maden.jpg|Larvae of the onion fly

File:Urocystis colchici var. cepulae on an onion seedling.jpg|Onion smut, Urocystis colchici var. cepulae, on a seedling

File:Zwiebel Blattfleckenkrankheit (Cladosporium allii-cepae) Anamorph - Noé López G.LLG-Bernburg.jpg|Onion leaf spot caused by Cladosporium allii-cepae

File:Onion (Allium cepa) Bacterial soft rot (42052268015).jpg|Bacterial soft rot caused by Erwinia carotovora subsp. carotovora

File:Zwiebel Schmutzfleckenkrankheit (Colletotrichum dematium f. sp. circinans) - G-Bedlan, Wien.jpg|Anthracnose caused by Colletotrichum dematium subsp. circinans

Onion oil is authorised for use in the European Union for use as a pesticide against carrot fly in umbelliferous crops (carrots, parsnips, parsley, celery, celeriac).{{Cite web |last=European Commission |date=20 July 2018 |title=Final Review report for the basic substance Onion Oil finalised in the Standing Committee on Plants, Animals, Food and Feed at its meeting on 20 July 2018 in view of the approval of onion oil as basic substance in accordance with Regulation (EC) No 1107/2009 |url=https://mst.dk/media/171096/review-report-for-onion-oil-juli-2018.pdf |url-status=live |archive-url=https://web.archive.org/web/20211123111251/https://mst.dk/media/171096/review-report-for-onion-oil-juli-2018.pdf |archive-date=23 November 2021 |access-date=23 November 2021}}

File:Onion grading at the Centre for Agroecology, Water and Resilience (CAWR), Coventry University.webm, England, using a manually-operated sorter]]

Onions are a widely cultivated vegetable crop, produced in the second largest quantity after tomatoes.{{Cite book |last=Ray |first=Ramesh C. |url=https://books.google.com/books?id=sWH8EAAAQBAJ&dq=global+onion+cultivation&pg=PA283 |title=Roots, Tubers, and Bulb Crop Wastes: Management by Biorefinery Approaches |date=2024 |publisher=Springer Nature |isbn=978-981-99-8266-0 |page=283}} In 2021, the top global producers of onions were China, India, the United States, and Turkey.{{Cite journal |last1=Ochar |first1=Kingsley |last2=Kim |first2=Seong-Hoon |date=2023-09-18 |title=Conservation and Global Distribution of Onion (Allium cepa L.) Germplasm for Agricultural Sustainability |journal=Plants |volume=12 |issue=18 |page=3294 |doi=10.3390/plants12183294 |doi-access=free |pmid=37765458 |pmc=10535454 |bibcode=2023Plnts..12.3294O }} In 2022, world production of onions and shallots (as green produce) was 5.0 million tonnes, led by China with 17% of the total, and Mali, Angola, and Japan as secondary producers.

In the home, cooking onions and sweet onions are best stored at room temperature, optimally in a single layer, in large mesh bags in a dry, cool, dark, well-ventilated location. In this environment, cooking onions have a shelf life of three to four weeks and sweet onions one to two weeks. Cooking onions will absorb odours from apples and pears. Additionally, they draw moisture from vegetables with which they are stored which may cause them to decay.{{cite web |url=http://www.extension.iastate.edu/news/2009/jul/062201.htm |title=Harvesting and storing onions |last=Jauron |first=Richard |date=2009-07-27 |publisher=Iowa State University Extension |access-date=2013-03-28 |archive-date=18 May 2013 |archive-url=https://web.archive.org/web/20130518151139/http://www.extension.iastate.edu/news/2009/jul/062201.htm |url-status=live }}

Sweet onions have a greater water and sugar content than cooking onions. This makes them sweeter and milder tasting, but reduces their shelf life. Sweet onions can be stored refrigerated; they have a shelf life of around one month. Irrespective of type, any cut pieces of onion are best tightly wrapped, stored away from other produce, and used within two to three days.

{{further|List of onion cultivars}}

File:Cipollatropea.jpg

Most of the diversity within A. cepa occurs within this group, the most economically important Allium crop. Plants within this group form large single bulbs, and are grown from seed or seed-grown sets. The majority of cultivated varieties grown for dry bulbs, salad onions, and pickling onions belong to this group.{{sfn|Fritsch|2002|pp=20–21}} The range of diversity found among these cultivars includes variation in photoperiod (length of day that triggers bulbing), storage life, flavour, and skin colour.{{cite book |last=Brewster |first=James L. |title=Onions and other vegetable Alliums |edition=1st |year=1994 |publisher=CAB International |location=Wallingford, UK |isbn=978-0-85198-753-8 |page=5}}

This group contains shallots and potato onions, also referred to as multiplier onions. The bulbs are smaller than those of common onions, and a single plant forms an aggregate cluster of several bulbs from a master. They are propagated almost exclusively from daughter bulbs, although reproduction from seed is possible. Shallots are the most important subgroup within this group and comprise the only cultivars cultivated commercially. They form aggregate clusters of small, narrowly ovoid to pear-shaped bulbs. Potato onions differ from shallots in forming larger bulbs with fewer bulbs per cluster, and having a flattened (onion-like) shape. Intermediate forms exist.{{sfn|Fritsch|2002|pp=20–21}}

I'itoi onion is a prolific multiplier onion cultivated in the Baboquivari Peak Wilderness, Arizona area. This small-bulb type has a shallot-like flavour and is easy to grow and ideal for hot, dry climates. Bulbs are separated, and planted in the fall {{convert|1|in|mm|order=flip|0|abbr=on}} below the surface and {{convert|12|in|mm|order=flip|sigfig=1|abbr=on}} apart. Bulbs will multiply into clumps and can be harvested throughout the cooler months. Tops die back in the heat of summer and may return with heavy rains; bulbs can remain in the ground or be harvested and stored in a cool dry place for planting in the fall. The plants rarely flower; propagation is by division.{{cite web |url=http://www.slowfoodusa.org/index.php/programs/ark_product_detail/iitoi_onion/ |title=I'Itoi Onion |year=2010 |website=Ark of Taste |publisher=Slow Food USA |access-date=2013-03-25 |archive-date=23 August 2013 |archive-url=https://web.archive.org/web/20130823061009/http://www.slowfoodusa.org/index.php/programs/ark_product_detail/iitoi_onion |url-status=dead}}

File:Sint Jansui (Allium fistulosum var. bulbifera).jpg

Some hybrids are cultivated that have A. cepa parentage, such as the diploid tree onion or Egyptian onion (A. ×proliferum), and the triploid onion (A. ×cornutum).{{cite journal |author=Friesen, N. & M. Klaas |year=1998 |title=Origin of some vegetatively propagated Allium crops studied with RAPD and GISH. |journal=Genetic Resources and Crop Evolution |volume=45 |issue=6 | pages=511–523 |doi=10.1023/A:1008647700251 |s2cid=26205471 }}

The tree onion or Egyptian onion produces bulblets in the umbel instead of flowers, and is now known to be a hybrid of A. cepa and A. fistulosum. It has previously been treated as a variety of A. cepa, for example A. cepa var. proliferum, A. cepa var. bulbiferum, and A. cepa var. viviparum.{{GRIN |Allium × proliferum |404736 |access-date=21 February 2011}}{{sfn|Fritsch|2002|p=19}} It has been grown for centuries in Japan and China for use as a salad onion.{{cite book |last=Brewster |first=James L. |title=Onions and other vegetable Alliums |edition=1st |year=1994 |publisher=CAB International |location=Wallingford, UK |isbn=978-0-85198-753-8 |page=15}}{{sfn|Fritsch|2002|pp=9–10}}

The triploid onion is a hybrid species with three sets of chromosomes, two sets from A. cepa and the third set from an unknown parent.{{sfn|Fritsch|2002|p=19}} Various clones of the triploid onion are grown locally in different regions, such as 'Ljutika' in Croatia, and 'Pran', 'Poonch', and 'Srinagar' in the India-Kashmir region. 'Pran' is grown extensively in the northern Indian provinces of Jammu and Kashmir. There are very small genetic differences between 'Pran' and the Croatian clone 'Ljutika', implying a monophyletic origin for this species.{{cite journal |last1=Friesen |first1=N. |last2=Klaas |first2=M. |s2cid=26205471 |year=1998 |title=Origin of some vegetatively propagated Allium crops studied with RAPD and GISH |journal=Genetic Resources and Crop Evolution |volume=45 |issue=6 |pages=511–523 |doi=10.1023/A:1008647700251}}

Spring onions or salad onions may be grown from the Welsh onion (A. fistulosum), as well as from A. cepa. Young plants of A. fistulosum and A. cepa look very similar, but may be distinguished by their leaves, which are circular in cross-section in A. fistulosum rather than flattened on one side.{{cite book |last=Brewster |first=James L. |title=Onions and other vegetable alliums |edition=1st |year=1994 |publisher=CAB International |location=Wallingford, UK |isbn=978-0-85198-753-8 |page=3}}

File:Onion seller in Heath Street - geograph.org.uk - 1072379.jpg, his bicycle laden with onions and garlic, in London, 2008]]

The name 'the Big Onion' was formerly used of New York City, before it became 'the Big Apple', and Chicago became 'the Big Onion'.

The 10th century Exeter Book, written in Old English, contains a riddle which seems to be about an onion, with sexual overtones. The "wondrous creature, a joy to women" stands "in a bed"; "My column is erect and tall"; a woman "rubs me to redness" but at once "she feels my meeting"; the riddle ends "Wet will be that eye."{{cite web |last=Cavell |first=Megan |title=Exeter Riddle 25 |url=https://theriddleages.bham.ac.uk/riddles/tag/riddle%2025/ |publisher=University of Birmingham |access-date=14 October 2024 |date=26 June 2014}}

In the Odyssey, Homer included the lines "I saw the shining tunic about his skin, like the skin of a dried onion, so soft was it, and it shone in the sun".Homer, Odyssey 19, lines 232-234. R. Drew Griffith comments that the double comparison of the tunic that Penelope gave to the disguised Odysseus to onion and sun "risks being funny", and notes that Theopompus indeed found it "ridiculous". Griffith suggests that Homer included the onion because of its capacity to produce tears, hinting at Penelope's sorrow at Odysseus's long absence.{{cite journal |last=Griffith |first=R. Drew |title=His tunic was like an onion or the sun (Odyssey 19, 232-234) |journal=Quaderni Urbinati di Cultura Classica |language=English |volume=109 |issue=1 |year=2015 |jstor=24645248}}

Onion Johnnies were Breton farmers and agricultural labourers who travelled from Roscoff in Brittany, originally on foot and later on bicycles, selling strings of distinctive pink onions door to door in Britain.{{cite web |title=The history of the Johnnies of Roscoff |url=https://www.brittany-ferries.co.uk/holidays/experience/the-johnnies |publisher=Brittany Ferries |access-date=14 October 2024 |url-status=live |archive-date=21 September 2022 |archive-url=https://web.archive.org/web/20220921173120/https://www.brittany-ferries.co.uk/holidays/experience/the-johnnies}}

In India, when the price of onions became very high in 2015, the Hindustan Times recorded that people shared many onion jokes, such as the punning {{lang|hi|प्या (र)ज़ लो, प्याज़ दो|}} ({{transliteration|hi|pya (r)z lo, pyaz do}}, "take love, give me onions").{{cite news |last1=Kaur |first1=Harpreet |title=Online onion humour brings tears of joy on Raksha Bandhan |url=https://www.hindustantimes.com/punjab/online-onion-humour-brings-tears-of-joy-on-raksha-bandhan/story-KEJ1Zm546jnIgNTjZ9nh9M.html |access-date=14 October 2024 |work=Hindustan Times |date=29 August 2015}}

• List of Allium species
• Pyruvate scale

{{reflist}}

• {{cite book |last1=Fritsch |first1=Reinhard M. |last2=Friesen |first2=Nikolai |title=Allium Crop Science: Recent Advances |publisher=CABI Publishing |year=2002 |isbn=0-85199-510-1 |editor-last=Rabinowitch |editor-first=Haim D. |location=Wallingford, UK |chapter=Chapter 1: Evolution, Domestication, and Taxonomy |doi=10.1079/9780851995106.0005 |oclc=228168061 |s2cid=189956991 |editor-last2=Currah |editor-first2=Lesley |ref={{harvid|Fritsch|2002}} }}

• {{cite book |last=Block |first=E. |title=Garlic and Other Alliums: The Lore and the Science |publisher=Royal Society of Chemistry |year=2010 |isbn=978-0-85404-190-9 |ref=none}}
• {{cite book |last=Sen |first=Colleen T. |year=2004 |title=Food culture in India |publisher=Greenwood Publishing |isbn=0-313-32487-5 |ref=none}}

{{Sister project links

|b= |c= |n= no|q=no |s=1911 Encyclopædia Britannica/Onion |v=no |wikt= onion

|d= |iw= |m= |mw= |species=yes |species_author= |voy=

|commonscat= Allium cepa

|cookbook= Onion

}}

• {{Commons category-inline|Onions in art}}
• {{Cookbook-inline|Onion powder}}
• [https://web.archive.org/web/20140301113518/http://database.prota.org/dbtw-wpd/exec/dbtwpub.dll?AC=QBE_QUERY&BU=http%3A%2F%2Fdatabase.prota.org%2Fsearch.htm&TN=PROTAB~1&QB0=AND&QF0=Species+Code&QI0=Allium+cepa&RF=Webdisplay PROTAbase on Allium cepa] (archived 1 March 2014)

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{{Allium}}

{{Transient receptor potential channel modulators}}

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