lettuce

File:Lactuca sativa seeds.jpg

Lactuca sativa is a member of the Lactuca (lettuce) genus and the Asteraceae (sunflower or aster) family.{{cite web|url=https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=36607|title=Lactuca sativa L|publisher=Integrated Taxonomic Information System|access-date=27 March 2010|archive-url=https://web.archive.org/web/20111025171631/http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=36607|archive-date=25 October 2011|url-status=live}} The species was first described in 1753 by Carl Linnaeus in the second volume of his Species Plantarum.{{cite web|url=http://www.nhm.ac.uk/our-science/data/linnaean-typification/search/detail.dsml?ID=492400&listPageURL=list%2edsml%3fVarqtype%3dstarts%2bwith%26CVarqtype%3dstarts%2bwith%26CGenusqtype%3dstarts%2bwith%26CSpeciesqtype%3dstarts%2bwith%26Species%3dsativa%26sort%3dGenus%252cSpecies%26Speciesqtype%3dequals%26Genus%3dLactuca%26Genusqtype%3dstarts%2bwith%26CSspqtype%3dstarts%2bwith|title=The Linnaean Plant Name Typification Project|year=2022 |publisher=Natural History Museum|doi=10.5519/qwv6u7j5 |access-date=17 December 2015|archive-url=https://web.archive.org/web/20151222085030/http://www.nhm.ac.uk/our-science/data/linnaean-typification/search/detail.dsml?ID=492400&listPageURL=list%2edsml%3fVarqtype%3dstarts%2bwith%26CVarqtype%3dstarts%2bwith%26CGenusqtype%3dstarts%2bwith%26CSpeciesqtype%3dstarts%2bwith%26Species%3dsativa%26sort%3dGenus%252cSpecies%26Speciesqtype%3dequals%26Genus%3dLactuca%26Genusqtype%3dstarts%2bwith%26CSspqtype%3dstarts%2bwith|archive-date=22 December 2015|url-status=live |author1=Natural History Museum }} Synonyms for L. sativa include Lactuca scariola {{abbr|var.|variety}} sativa, L. scariola {{abbr|var.|variety}} integrata and L. scariola {{abbr|var.|variety}} integrifolia.{{cite web|url=http://plants.usda.gov/java/profile?symbol=LASA3|title=Lactuca sativa L|publisher=United States Department of Agriculture|access-date=2 April 2012|archive-url=https://web.archive.org/web/20120608120552/http://plants.usda.gov/java/profile?symbol=LASA3|archive-date=8 June 2012|url-status=dead}} L. scariola is itself a synonym for L. serriola, the common wild or prickly lettuce.{{cite web|url=http://plants.usda.gov/java/profile?symbol=LASE|title=Lactuca serriola L|publisher=United States Department of Agriculture|access-date=2 April 2012|archive-url=https://web.archive.org/web/20120605153004/http://plants.usda.gov/java/profile?symbol=LASE|archive-date=5 June 2012|url-status=dead}} L. sativa also has many identified taxonomic groups, subspecies and varieties, which delineate the various cultivar groups of domesticated lettuce.{{cite web|url=http://www.ars-grin.gov/misc/mmpnd/Lactuca.html|title=Sorting Lactuca Names|work=Multilingual Multiscript Plant Name Database|publisher=University of Melbourne|author=Porcher, Michael H.|access-date=2 April 2012|year=2005|url-status=dead|archive-url=https://web.archive.org/web/20120916125457/http://www.ars-grin.gov/misc/mmpnd/Lactuca.html|archive-date=16 September 2012}} Lettuce is closely related to several Lactuca species from southwest Asia; the closest relationship is to L. serriola, an aggressive weed common in temperate and subtropical zones in much of the world.{{cite book|url=https://books.google.com/books?id=1hHSYoqY-AwC&pg=PA157|title=Domestication of Plants in the Old World: The Origin and Spread of Domesticated Plants in Southwest Asia, Europe, and the Mediterranean Basin|author1=Zohary, Daniel|author2=Hopf, Maria|author3=Weiss, Ehud|publisher=Oxford University Press|year=2012|isbn=978-0-19-954906-1|page=157|access-date=10 January 2016|archive-date=23 July 2016|archive-url=https://web.archive.org/web/20160723001748/https://books.google.com/books?id=1hHSYoqY-AwC&pg=PA157|url-status=live}}

The Romans referred to lettuce as {{lang|la|lactuca}} ({{lang|la|lac}} meaning "milk" in Latin), an allusion to the white substance, latex, exuded by cut stems.{{Cite book |last=Weaver |first=William Woys |title=Heirloom vegetable gardening: a master gardener's guide to planting, growing, seed saving, and cultural history |date=1997 |publisher=Henry Holt and Company |isbn=978-0-8050-4025-8 |edition=1st |location=New York |pages=170–172}} The name Lactuca has become the genus name, while {{lang|la|sativa}} (meaning "sown" or "cultivated") was added to create the species name.Katz and Weaver, p. 376. The current word lettuce, originally from Middle English, came from the Old French {{lang|fro|letues}} or {{lang|fro|laitues}}, which derived from the Roman name.{{cite book|page=[https://archive.org/details/oxforddictionary0000unse_x2z7/page/300 300]|title=The Oxford Dictionary of Word Histories|editor=Chantrell, Glynnis|publisher=Oxford University Press|year=2002|isbn=0-19-863121-9|url=https://archive.org/details/oxforddictionary0000unse_x2z7/page/300}} The name romaine came from the variety of lettuce grown in the Roman papal gardens, while {{Lang|la|cos}}, another term for romaine lettuce, came from the earliest European seeds of the type from the Greek island of Kos, a center of lettuce farming in the Byzantine period.{{Cite book |last=Weaver |first=William Woys |title=Heirloom vegetable gardening: a master gardener's guide to planting, growing, seed saving, and cultural history |date=1997 |publisher=Henry Holt and Company |isbn=978-0-8050-4025-8 |edition=1st |location=New York |page=172}}

File:Lactuca sativa, botersla.jpg

File:Kropsla vruchten (Lactuca sativa fruits).jpg in fruit]]

File:Lettuce seeds 01.jpg

Lettuce's native range spreads from the Mediterranean to Siberia, although it has been transported to almost all areas of the world. Plants generally have a height and spread of {{convert|15|to|30|cm|abbr=on|0}}.{{cite web|url=http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/plant-finder/plant-details/kc/a679/lactuca-sativa.aspx|title=Lactuca sativa|publisher=Missouri Botanical Garden|access-date=27 March 2012|archive-url=https://web.archive.org/web/20130616211830/http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/plant-finder/plant-details/kc/a679/lactuca-sativa.aspx|archive-date=16 June 2013|url-status=live}} The leaves are colorful, mainly in the green and red color spectrums, with some variegated varieties. There are also a few varieties with yellow, gold or blue-teal leaves.{{cite book|chapter-url=http://www.hort.purdue.edu/newcrop/proceedings1993/v2-528.html|chapter=New Directions in Salad Crops: New Forms, New Tools, and Old Philosophy|author1=Ryder, J.|author2=Waycott, Williams|year=1993|pages=528–532|editor-last1=Janick|editor-first1=J. |editor-last2= Simon|editor-first2= J.E.|title=New Crops|publisher=Wiley|access-date=11 April 2012|archive-url=https://web.archive.org/web/20120717013724/http://www.hort.purdue.edu/newcrop/proceedings1993/v2-528.html|archive-date=17 July 2012|url-status=dead}}

Lettuces have a wide range of shapes and textures, from the dense heads of the iceberg type to the notched, scalloped, frilly or ruffly leaves of leaf varieties.{{cite book|url=https://books.google.com/books?id=eAyNxv2I1LoC&q=lettuce+leaf+color+range&pg=PA28|page=28|title=Fine Cooking in Season: Your Guide to Choosing and Preparing the Season's Best|publisher=Taunton Press|year=2011|isbn=978-1-60085-303-6|author=Fine Cooking Magazine|access-date=6 October 2020|archive-date=20 May 2021|archive-url=https://web.archive.org/web/20210520044644/https://books.google.com/books?id=eAyNxv2I1LoC&q=lettuce+leaf+color+range&pg=PA28|url-status=live}} Lettuce plants have a root system that includes a main taproot and smaller secondary roots. Some varieties, especially those found in the United States and Western Europe, have long, narrow taproots and a small set of secondary roots. Longer taproots and more extensive secondary systems are found in varieties from Asia.

Depending on the variety and time of year, lettuce generally lives 65–130 days from planting to harvesting. Because lettuce that flowers (through the process known as "bolting") becomes bitter and unsaleable, plants grown for consumption are rarely allowed to grow to maturity. Lettuce flowers more quickly in hot temperatures, while freezing temperatures cause slower growth and sometimes damage to outer leaves.{{cite web |url=http://ucanr.org/freepubs/docs/7216.pdf |title=Leaf Lettuce Production in California |author1=Smith, Richard |author2=Cahn, Michael |author3=Daugovish, Oleg |author4=Koike, Steven |author5=Natwick, Eric |author6=Smith, Hugh |author7=Subbarao, Krishna |author8=Takele, Etaferahu |author9=Turin, Thomas |publisher=University of California Vegetable Research and Information Center |access-date=11 April 2012 |archive-url=https://web.archive.org/web/20120619050116/http://ucanr.org/freepubs/docs/7216.pdf |archive-date=19 June 2012 |url-status=dead }}

Once plants move past the edible stage, they develop flower stalks up to {{convert|1|m|sigfig=1|abbr=on}} high with small yellow blossoms. Like other members of the tribe Cichorieae, lettuce inflorescences (also known as flower heads or capitula) are composed of multiple florets, each with a modified calyx called a pappus (which becomes the feathery "parachute" of the fruit), a corolla of five petals fused into a ligule or strap, and the reproductive parts. These include fused anthers that form a tube which surrounds a style and bipartite stigma. As the anthers shed pollen, the style elongates to allow the stigmas, now coated with pollen, to emerge from the tube.{{eFloras|1|20701|Asteraceae tribe Cichorieae |first1=Theodore M. |last1=Barkley |first2=Luc |last2=Brouillet |first3=John L. |last3=Strother |volume=19, 20 and 21 |access-date=24 September 2012}} The ovaries form compressed, obovate (teardrop-shaped) dry fruits that do not open at maturity, measuring 3 to 4 mm long. The fruits have 5–7 ribs on each side and are tipped by two rows of small white hairs. The pappus remains at the top of each fruit as a dispersal structure. Each fruit contains one seed, which can be white, yellow, gray or brown depending on the variety of lettuce.{{cite web|url=http://www.kew.org/science-research-data/kew-in-depth/difficult-seeds/species-profiles/lactuca-sativa/index.htm|archive-url=https://web.archive.org/web/20121102090341/http://www.kew.org/science-research-data/kew-in-depth/difficult-seeds/species-profiles/lactuca-sativa/index.htm|archive-date=2012-11-02|title=Lactuca sativa|publisher=Kew Royal Botanical Gardens|access-date=2 April 2012}}

The domestication of lettuce over the centuries has resulted in several changes through selective breeding: delayed bolting, larger seeds, larger leaves and heads, better taste and texture, a lower latex content, and different leaf shapes and colors. Work in these areas continues through the present day.Davey, et al., pp. 222–225. Scientific research into the genetic modification of lettuce is ongoing, with over 85 field trials taking place between 1992 and 2005 in the European Union and the United States to test modifications allowing greater herbicide tolerance, greater resistance to insects and fungi and slower bolting patterns. However, genetically modified lettuce is not currently used in commercial agriculture.{{cite web|url=http://www.gmo-compass.org/eng/database/plants/65.lettuce.html|title=Lettuce|publisher=GMO Compass|access-date=3 April 2012|url-status=dead|archive-url=https://web.archive.org/web/20120511202430/http://www.gmo-compass.org/eng/database/plants/65.lettuce.html|archive-date=11 May 2012}}

File:Romaine lettuce.jpg, a descendant of some of the earliest cultivated lettuce]]

DNA analysis of 445 types of lettuce indicates that lettuce was first domesticated from its wild ancestor near the Caucasus, where seed shattering was first selected out of the cultivar. At this time, the lettuce plant was only suitable for harvesting its seeds, which could be pressed to extract oil, likely used for cooking, among other purposes.{{Cite journal |last1=Wei |first1=Tong |last2=van Treuren |first2=Rob |last3=Liu |first3=Xinjiang |last4=Zhang |first4=Zhaowu |last5=Chen |first5=Jiongjiong |last6=Liu |first6=Yang |last7=Dong |first7=Shanshan |last8=Sun |first8=Peinan |last9=Yang |first9=Ting |last10=Lan |first10=Tianming |last11=Wang |first11=Xiaogang |last12=Xiong |first12=Zhouquan |last13=Liu |first13=Yaqiong |last14=Wei |first14=Jinpu |last15=Lu |first15=Haorong |date=2021-04-12 |title=Whole-genome resequencing of 445 Lactuca accessions reveals the domestication history of cultivated lettuce |url=https://www.nature.com/articles/s41588-021-00831-0 |journal=Nature Genetics |language=en |volume=53 |issue=5 |pages=752–760 |doi=10.1038/s41588-021-00831-0 |pmid=33846635 |issn=1546-1718|url-access=subscription }}{{Cite web |last=van Treuren |first=Rob |date=2021-04-12 |title=The DNA of lettuce unravelled: in 6000 years from weed to beloved vegetable |url=https://www.wur.nl/en/newsarticle/the-dna-of-lettuce-unravelled-in-6000-years-from-weed-to-beloved-vegetable.htm |access-date=2024-10-22 |website=Wageningen University & Research}} From there, lettuce was likely transported to the Near East and then to ancient Egypt, where the first depictions of lettuce cultivation can be found as early as 2680 BC. Like the early lettuce from the Caucasus, this lettuce was grown to produce cooking oil from its seeds.{{Cite book |last1=Katz |first1=Solomon H. |url=https://books.google.com/books?id=CAtXswEACAAJ |title=Encyclopedia of Food and Culture |last2=Weaver |first2=William Woys |publisher=Scribner |year=2003 |isbn=978-0-684-80568-9 |volume=2 |pages=375–376 |language=en}}

Lettuce was considered a sacred plant of the reproduction god Min, and was carried during his festivals and placed near his images. The plant was thought to help the god "perform the sexual act untiringly".{{cite book |author=Hart, George |url=https://books.google.com/books?id=Q1LAiPylZm4C&q=lettuce+in+egyptian+ritual&pg=PA95 |title=The Routledge Dictionary of Egyptian Gods and Goddesses |publisher=Routledge |year=2005 |isbn=1-134-28424-1 |edition=2nd |page=95 |access-date=6 October 2020 |archive-url=https://web.archive.org/web/20210928054557/https://books.google.com/books?id=Q1LAiPylZm4C&q=lettuce+in+egyptian+ritual&pg=PA95 |archive-date=28 September 2021 |url-status=live}} Its use in religious ceremonies resulted in the creation of many images in tombs and wall paintings. The cultivated variety appears to have been about {{convert|75|cm|abbr=on}} tall and resembled a large version of the modern romaine lettuce. These upright lettuces were developed by the Egyptians and passed to the Greeks, who in turn shared them with the Romans.{{Citation needed|date=October 2024}} Around 50 AD, Roman agriculturalist Columella described several lettuce varieties – some of which may have been ancestors of today's lettuces.

The plant was eventually selectively bred into a plant grown for its edible leaves. The long leaves in Egyptian depictions suggest that it may have been grown for its leaves, which would make it the first lettuce cultivar grown for this purpose. However, genome wide analysis suggests the traits needed for cultivation as a leafy vegetable, like the loss of bitterness and thorns, evolved much later, from around 500 BC in Southern Europe. Lettuce cultivars radiated more rapidly from this point, with oilseed lettuce likely being brought by the ancient Greeks from Egypt to Italy, where it was modified into cos lettuce and cultivated for its leaves. From there, it was brought north to Central Europe, where it was modified into butterhead lettuce and other varieties.

Lettuce appears in many medieval writings, especially as a medicinal herb. Hildegard of Bingen mentioned it in her writings on medicinal herbs between 1098 and 1179, and many early herbals also describe its uses. In 1586, Joachim Camerarius provided descriptions of the three basic modern lettuces – head lettuce, loose-leaf lettuce, and romaine (or cos) lettuce. Lettuce was first brought to the Americas from Europe by Christopher Columbus in the late 15th century.{{cite book|chapter-url=https://books.google.com/books?id=DxrMm9lMFUAC&q=Christopher+Columbus+lettuce+new+world&pg=PA313|chapter=Lettuce Diseases: Ecology and Control|author1=Subbarao, Krishna V.|author2=Koike, Steven T.|title=Encyclopedia of Pest Management, Volume 2|editor=Pimentel, David|publisher=CRC Press|year=2007|isbn=978-1-4200-5361-6|page=313|access-date=6 October 2020|archive-date=28 September 2021|archive-url=https://web.archive.org/web/20210928054449/https://books.google.com/books?id=DxrMm9lMFUAC&q=Christopher+Columbus+lettuce+new+world&pg=PA313|url-status=live}} Between the late 16th century and the early 18th century, many varieties were developed in Europe, particularly Holland. Books published in the mid-18th and early 19th centuries describe several varieties found in gardens today.

Due to its short lifespan after harvest, lettuce was originally sold relatively close to where it was grown. The early 20th century saw the development of new packing, storage and shipping technologies that improved the lifespan and transportability of lettuce and resulted in a significant increase in availability.{{cite book |last1=Twilley |first1=Nicola |title=Frostbite: How Refrigeration Changed Our Food, Our Planet, and Ourselves |date=2024 |publisher=Penguin Press |location=New York |isbn=9780735223288 |pages=124–131 |edition=1st}}{{citation needed|date=April 2024}} During the 1950s, lettuce production was revolutionized with the development of vacuum cooling, which allowed field cooling and packing of lettuce, replacing the previously used method of ice-cooling in packing houses outside the fields.{{cite journal|url=http://ucce.ucdavis.edu/files/repositoryfiles/ca1011p3-64576.pdf|title=House Packing Western Lettuce|author1=Enochian, R.V.|author2=Smith, F.J|journal=California Agriculture|date=November 1956|url-status=dead|archive-url=https://web.archive.org/web/20130615003744/http://ucce.ucdavis.edu/files/repositoryfiles/ca1011p3-64576.pdf|archive-date=15 June 2013|df=dmy-all}}

Lettuce is easy to grow, and as such has been a significant source of sales for many seed companies. Tracing the history of many varieties is complicated by the practice of many companies, particularly in the US, of changing a variety's name from year to year. This practice is conducted for several reasons, the most prominent being to boost sales by promoting a "new" variety, or to prevent customers from knowing that the variety had been developed by a competing seed company. Documentation from the late 19th century shows between 65 and 140 distinct varieties of lettuce, depending on the amount of variation allowed between types – a distinct difference from the 1,100 named lettuce varieties on the market at the time. Names also often changed significantly from country to country.Weaver, pp. 173–174. Although most lettuce grown today is used as a vegetable, a minor amount is used in the production of tobacco-free cigarettes; however, domestic lettuce's wild relatives produce a leaf that visually more closely resembles tobacco.Katz and Weaver, p. 377.

File:Park Lane Nurseries - geograph.org.uk - 583201.jpg

A hardy annual, some varieties of lettuce can be overwintered even in relatively cold climates under a layer of straw, and older, heirloom varieties are often grown in cold frames.Weaver, pp. 172–173. Lettuces meant for the cutting of individual leaves are generally planted straight into the garden in thick rows. Heading varieties of lettuces are commonly started in flats, then transplanted to individual spots, usually {{convert|20|to|36|cm|abbr=on}} apart, in the garden after developing several leaves. Lettuce spaced farther apart receives more sunlight, which improves color and nutrient quantities in the leaves. Pale to white lettuce, such as the centers in some iceberg lettuce, contain few nutrients.

File:Planche Lactuca sativa.jpg]]

Lettuce grows best in full sun in loose, nitrogen-rich soils with a pH of between 6.0 and 6.8. Heat generally prompts lettuce to bolt, with most varieties growing poorly above {{convert|24|C}}; cool temperatures prompt better performance, with {{convert|16|to|18|C}} being preferred and as low as {{convert|7|C}} being tolerated.Bradley, p. 129. Plants in hot areas that are provided partial shade during the hottest part of the day will bolt more slowly. Temperatures above {{convert|27|C}} will generally result in poor or non-existent germination of lettuce seeds. After harvest, lettuce lasts the longest when kept at {{convert|0|C}} and 96 percent humidity. The high water content of lettuce (94.9 percent) creates problems when attempting to preserve the plant – it cannot be successfully frozen, canned or dried and must be eaten fresh. In spite of its high water content, traditionally grown lettuce has a low water footprint, with {{convert|237|liters}} of water required for each kilogram of lettuce produced.{{cite book |last=Holden |first=Joseph |date=2013 |title=Water Resources: An Integrated Approach |url=https://www.routledge.com/Water-Resources-An-Integrated-Approach-1st-Edition/Holden/p/book/9780203489413 |publisher=Routledge |page=335 |isbn=9780203489413 |access-date=12 November 2019 |archive-date=5 June 2020 |archive-url=https://web.archive.org/web/20200605143046/https://www.routledge.com/Water-Resources-An-Integrated-Approach-1st-Edition/Holden/p/book/9780203489413 |url-status=live }} Hydroponic growing methods can reduce this water consumption by nearly two orders of magnitude.

Lettuce varieties will cross with each other, making spacing of {{convert|1.5|to|6|m|in|abbr=on|-1}} between varieties necessary to prevent contamination when saving seeds. Lettuce will also cross with Lactuca serriola (wild lettuce), with the resulting seeds often producing a plant with tough, bitter leaves. Celtuce, a lettuce variety grown primarily in Asia for its stems, crosses easily with lettuces grown for their leaves.Weaver, pp. 175–176. This propensity for crossing, however, has led to breeding programs using closely related species in Lactuca, such as L. serriola, L. saligna, and L. virosa, to broaden the available gene pool. Starting in the 1990s, such programs began to include more distantly related species such as L. tatarica.{{cite journal | title = Phylogenetic relationships among Lactuca (Asteraceae) species and related genera based on ITS-1 DNA sequences | author1 = Koopman, Wim J.M. | author2 = Guetta, Eli | author3 = van de Wiel, Clemens C.M. | author4 = Vosman, Ben | author5 = van den Berg, Ronald G | journal = American Journal of Botany | year = 1998 | volume = 85 | pages = 1517–1530 | doi = 10.2307/2446479 | jstor = 2446479 | issue = 11 | pmid = 21680311 | doi-access = free }}

File:Lettuce mix.jpgFile:Yangzhou - supermarket - woju - P1070028.JPG is grown for its stem, used in Chinese cooking.]]File:Buttercrunch butterhead lettuce.jpg

File:Salata Prajzerica (Croatia).jpg]]

Seeds keep best when stored in cool conditions, and, unless stored cryogenically, remain viable the longest when stored at {{convert|-20|C}}; they are relatively short lived in storage. At room temperature, lettuce seeds remain viable for only a few months. However, when newly harvested lettuce seed is stored cryogenically, this life increases to a half-life of 500 years for vaporized nitrogen and 3,400 years for liquid nitrogen; this advantage is lost if seeds are not frozen promptly after harvesting.Davey, et al., p. 241.

{{Anchor|Cultivars}}

File:Lactuca sativa 'Forellenschluss', Longwood Gardens 2023 01.jpg]]

There are several types and cultivars of lettuce. Categorization may sometimes refer to "leaf" versus "head", but there are seven main cultivar groups of lettuce, each including many varieties:

1. Leaf—Also known as looseleaf, cutting or bunching lettuce, this type has loosely bunched leaves and is the most widely planted. It is used mainly for salads.{{cite web|url=http://urbanext.illinois.edu/veggies/lettuce.cfm|title=Lettuce|publisher=University of Illinois Extension|access-date=25 March 2012|archive-url=https://web.archive.org/web/20120315133237/http://urbanext.illinois.edu/veggies/lettuce.cfm|archive-date=15 March 2012|url-status=dead}}
2. * Red leaf lettuce—A group of lettuce types with red leaves.
3. Romaine/Cos—Used mainly for salads and sandwiches, this type forms long, upright heads. This is the most often used lettuce in Caesar salads.{{cite web|url=http://www.fruitsandveggiesmatter.gov/month/lettuce.html|title=Vegetable of the Month: Lettuce|publisher=Centers for Disease Control and Prevention|access-date=26 March 2012|url-status=dead|archive-url=https://web.archive.org/web/20120322151027/http://www.fruitsandveggiesmatter.gov/month/lettuce.html|archive-date=22 March 2012|df=dmy-all}}
4. * Little Gem—a dwarf, compact romaine lettuce, popular in the UK.{{cite web |title=Lactuca sativa 'Little Gem' {{!}} lettuce (Cos) 'Little Gem' Annual Biennial/RHS Gardening |url=https://www.rhs.org.uk/plants/112416/i-lactuca-sativa-i-little-gem/details |website=www.rhs.org.uk |access-date=2022-11-14 |language=en-gb}}
5. Iceberg/Crisphead—The most popular type in the United States. Iceberg lettuce is very heat-sensitive and was originally developed in 1894 for growth in the northern United States by Burpee Seeds and Plants. It gets its name from the way it was transported in crushed ice, where the heads of lettuce looked like icebergs.{{cite news |title=Iceberg lettuce |date=July 3, 2007 |author=Renna |publisher=Tribune Publishing |work=Chicago Tribune |url=https://www.chicagotribune.com/news/ct-xpm-2007-07-04-0706290893-story.html |access-date=June 22, 2011}} Today, it ships well, but is low in flavor and nutritional content, being composed of even more water than other lettuce types.
6. Butterhead—Also known as Boston or Bibb lettuce, and traditionally in the UK as "round lettuce",{{cite web|title=Lettuce|url=https://realfood.tesco.com/glossary/lettuce.html|website=Tesco Real Food|publisher=Tesco|access-date=16 January 2017|archive-url=https://web.archive.org/web/20170118100805/https://realfood.tesco.com/glossary/lettuce.html|archive-date=18 January 2017|url-status=dead}} this type is a head lettuce with a loose arrangement of leaves, known for its sweet flavor and tender texture.
7. Summercrisp—Also called Batavian or French crisp, this lettuce is midway between the crisphead and leaf types. These lettuces tend to be larger, bolt-resistant and well-flavored.{{cite web|url=http://vegetables.wsu.edu/winterlettuce.html|title=Winter Lettuce|publisher=Washington State University|access-date=26 March 2012|author=Miles, Carol|archive-url=https://web.archive.org/web/20120411080540/http://vegetables.wsu.edu/WinterLettuce.html|archive-date=11 April 2012|url-status=dead}}
8. Celtuce/Stem—This type is grown for its seedstalk, rather than its leaves, and is used in Asian cooking, primarily Chinese, as well as stewed and creamed dishes.
9. Oilseed—This type is grown for its seeds, which are pressed to extract an oil mainly used for cooking. It has few leaves, bolts quickly and produces seeds around 50 percent larger than other types of lettuce.Katz and Weaver, p. 375.

The four main types in the Western world have been looseleaf, romaine, crisphead, and butterhead, with the others being intermediary or more exotic. The butterhead and crisphead types are sometimes known together as "cabbage" lettuce, because their heads are shorter, flatter, and more cabbage-like than romaine lettuces.{{Cite book|last=Rana|first=M. K.|url=https://books.google.com/books?id=QDgPEAAAQBAJ&q=The+butterhead+and+crisphead+types+are+sometimes+known+together+as+%22cabbage%22+lettuce,+because+their+heads+are+shorter,+flatter,+and+more+cabbage-like+than+romaine+lettuces&pg=PA173|title=Vegetable Crop Science|date=2017-10-02|publisher=CRC Press|isbn=978-1-351-65279-7|pages=173|language=en|access-date=28 September 2021|archive-date=28 September 2021|archive-url=https://web.archive.org/web/20210928054450/https://books.google.com/books?id=QDgPEAAAQBAJ&newbks=0&printsec=frontcover&pg=PA173&dq=The+butterhead+and+crisphead+types+are+sometimes+known+together+as+%22cabbage%22+lettuce%2C+because+their+heads+are+shorter%2C+flatter%2C+and+more+cabbage-like+than+romaine+lettuces&hl=en|url-status=live}}

File:Starr 081031-0356 Lactuca sativa.jpg]]

{{see also|List of lettuce diseases}}

Soil nutrient deficiencies can cause a variety of plant problems that range from malformed plants to a lack of head growth. Many insects are attracted to lettuce, including cutworms, which cut seedlings off at the soil line; wireworms and nematodes, which cause yellow, stunted plants; tarnished plant bugs and aphids, which cause yellow, distorted leaves; leafhoppers, which cause stunted growth and pale leaves; thrips, which turn leaves gray-green or silver; leafminers, which create tunnels within the leaves; flea beetles, which cut small holes in leaves and caterpillars, slugs and snails, which cut large holes in leaves. For example, the larvae of the ghost moth is a common pest of lettuce plants.{{Cite journal|last=Edwards|first=C. A.|date=May 1964|title=The bionomics of swift moths. I.—The ghost swift moth, Hepialus humuli (L.)|journal=Bulletin of Entomological Research|volume=55|issue=1|pages=147–160|doi=10.1017/S000748530004935X|issn=1475-2670}} Mammals, including rabbits and groundhogs, also eat the plants.Bradley, pp. 129–132. Lettuce contains several defensive compounds, including sesquiterpene lactones, and other natural phenolics such as flavonol and glycosides, which help to protect it against pests. Certain varieties contain more than others, and some selective breeding and genetic modification studies have focused on using this trait to identify and produce commercial varieties with increased pest resistance.{{cite web|url=http://www.reeis.usda.gov/web/crisprojectpages/198636.html|title=Developing Multi-Species Insect Resistance in Romaine Lettuce|publisher=United States Department of Agriculture|access-date=5 April 2012|archive-url=https://web.archive.org/web/20131019193634/http://www.reeis.usda.gov/web/crisprojectpages/198636.html|archive-date=19 October 2013|url-status=dead}}

Lettuce also suffers from several viral diseases, including big vein, which causes yellow, distorted leaves, and mosaic virus, which is spread by aphids and causes stunted plant growth and deformed leaves. Aster yellows are a disease-causing bacteria carried by leafhoppers, which causes deformed leaves. Fungal diseases include powdery mildew and downy mildew, which cause leaves to mold and die and bottom rot, lettuce drop and gray mold, which cause entire plants to rot and collapse. Bacterial diseases include Botrytis cinerea, for which UV-C treatments may be used: Vàsquez et al. 2017 find that phenylalanine ammonia-lyase activity, phenolic production, and B. cinerea resistance are increased by UV-C.{{cite journal | last1=Urban | first1=L. | last2=Chabane Sari | first2=D. | last3=Orsal | first3=B. | last4=Lopes | first4=M. | last5=Miranda | first5=R. | last6=Aarrouf | first6=J. | title=UV-C light and pulsed light as alternatives to chemical and biological elicitors for stimulating plant natural defenses against fungal diseases | journal=Scientia Horticulturae | publisher=Elsevier | volume=235 | year=2018 | issn=0304-4238 | doi=10.1016/j.scienta.2018.02.057 | pages=452–459 | bibcode=2018ScHor.235..452U | s2cid=90436989}} Crowding lettuce tends to attract pests and diseases. Weeds can also be an issue, as cultivated lettuce is generally not competitive with them, especially when directly seeded into the ground. Transplanted lettuce (started in flats and later moved to growing beds) is generally more competitive initially, but can still be crowded later in the season, causing misshapen lettuce and lower yields. Weeds also act as homes for insects and disease and can make harvesting more difficult.{{cite web|url=http://www.ipm.ucdavis.edu/PMG/r441700111.html|title=Lettuce: Integrated Weed Management|work=UC Pest Management Guidelines|publisher=University of California|date=August 2007|access-date=3 April 2012|archive-url=https://web.archive.org/web/20120707190840/http://www.ipm.ucdavis.edu/PMG/r441700111.html|archive-date=7 July 2012|url-status=dead}} Herbicides are often used to control weeds in commercial production. However, this has led to the development of herbicide-resistant weeds in lettuce cultivation.

In 2022, world production of lettuce (report combined with chicory) was 27 million tonnes, with China alone producing 55% of the total (table).

Lettuce is the only member of the genus Lactuca to be grown commercially.{{cite book|url=https://books.google.com/books?id=iPgTGhaGRl4C&pg=PA296|title=Vegetable Diseases: A Color Handbook|page=296|publisher=Gulf Professional Publishing|year=2006|author1=Koike, Steven T|author2=Gladders, Peter|author3=Paulus, Albert O.|isbn=0-12-373675-7|access-date=10 January 2016|archive-url=https://web.archive.org/web/20160430102732/https://books.google.com/books?id=iPgTGhaGRl4C&pg=PA296|archive-date=30 April 2016|url-status=live}} Although China is the top world producer of lettuce, the majority of the crop is consumed domestically.{{Cn|date=May 2025}}

Western Europe and North America were the original major markets for large-scale lettuce production. By the late 1900s, Asia, South America, Australia and Africa became more substantial markets. Different locations tended to prefer different types of lettuce, with butterhead prevailing in northern Europe and Great Britain, romaine in the Mediterranean and stem lettuce in China and Egypt. By the late 20th century, the preferred types began to change, with crisphead, especially iceberg, lettuce becoming the dominant type in northern Europe and Great Britain and more popular in western Europe. In the US, no one type predominated until the early 20th century, when crisphead lettuces began gaining popularity. After the 1940s, with the development of iceberg lettuce, 95 percent of the lettuce grown and consumed in the US was crisphead lettuce. By the end of the century, other types began to regain popularity and eventually made up over 30 percent of production.Katz and Weaver, p. 378. Stem lettuce was first developed in China, where it remains primarily cultivated.{{cite book|url=https://books.google.com/books?id=Fo087ZxohA4C&pg=PA148|title=Food in China: A Cultural and Historical Inquiry|author=Simoons, Frederick J.|pages=147–148|isbn=0-8493-8804-X|publisher=CRC Press|year=1991|access-date=22 March 2020|archive-date=26 December 2019|archive-url=https://web.archive.org/web/20191226104737/https://books.google.com/books?id=Fo087ZxohA4C&pg=PA148|url-status=live}}

File:Lettuce plant reaching for the sky.jpg]]

In the early 21st century, bagged salad products increased in the lettuce market, especially in the US where innovative packaging and shipping methods prolonged freshness.{{cite journal|title=Lettuce Grows into A Processed Food|url=https://www.latimes.com/archives/la-xpm-2002-aug-19-fi-lettuce19-story.html|journal=Los Angeles Times|author=Fulmer, Melinda|date=19 August 2002|access-date=30 June 2012|archive-url=https://web.archive.org/web/20131218114512/http://articles.latimes.com/2002/aug/19/business/fi-lettuce19|archive-date=18 December 2013|url-status=live}}{{Cite news |url=https://www.npr.org/sections/thesalt/2016/07/12/485098252/as-bagged-salad-kits-boom-americans-eat-more-greens |title=As Bagged Salad Kits Boom, Americans Eat More Greens |last1=Charles |first1=Dan |last2=Aubrey |first2=Allison |newspaper=NPR.org |publisher=National Public Radio |date=12 July 2016 |access-date=5 April 2018 |archive-url=https://web.archive.org/web/20180403101039/https://www.npr.org/sections/thesalt/2016/07/12/485098252/as-bagged-salad-kits-boom-americans-eat-more-greens |archive-date=3 April 2018 |url-status=live }}

In the United States in 2022, lettuce was the main vegetable ingredient in salads, and was the most consumed among leaf vegetables; its market was about 20% of all vegetables, with Romaine and iceberg having about equal sales.{{cite web | url=https://www.ers.usda.gov/data-products/chart-gallery/gallery/chart-detail/?chartId=106516 | title=Lettuce | publisher=Agricultural Marketing Resource Center, Iowa State University | date=April 2023 | access-date=16 April 2024}} Some 85% of the lettuce consumed in the United States in 2022 was produced domestically.

As described around 50 AD, lettuce leaves were often cooked and served by the Romans with an oil-and-vinegar dressing; however, smaller leaves were sometimes eaten raw. During the 81–96 AD reign of Domitian, the tradition of serving a lettuce salad before a meal began. Post-Roman Europe continued the tradition of poaching lettuce, mainly with large romaine types, as well as the method of pouring a hot oil and vinegar mixture over the leaves.Weaver, pp. 170–172.

Today, the majority of lettuce is grown for its leaves, although one type is grown for its stem and one for its seeds, which are made into an oil. Most lettuce is used in salads, either alone or with other greens, vegetables, meats and cheeses. Romaine lettuce is often used for Caesar salads. Lettuce leaves can also be found in soups, sandwiches and wraps, while the stems are eaten both raw and cooked.

{{nutritional value | name=Lettuce (iceberg, raw)

| water=95.6 g

| kJ=58

| protein=0.9 g

| fat=0.14 g

| carbs=3.0 g

| fiber=1.2 g

| sugars=2.0 g

| calcium_mg=18

| iron_mg=0.41

| magnesium_mg=7

| phosphorus_mg=20

| potassium_mg=141

| sodium_mg=10

| zinc_mg=0.15

| manganese_mg=0.125

| vitC_mg=2.8

| thiamin_mg=0.041

| riboflavin_mg=0.025

| pantothenic_mg=0.091

| vitB6_mg=0.042

| folate_ug=29

| vitA_ug=25

| betacarotene_ug=299

| lutein_ug=277

| vitE_mg=0.18

| vitK_ug=24.1

| source_usda=1

| note=[https://fdc.nal.usda.gov/fdc-app.html#/food-details/169248/nutrients Link to USDA Database entry]

}}

The consumption of lettuce in China developed differently from in Western countries, due to health risks and cultural aversion to eating raw leaves; Chinese "salads" are composed of cooked vegetables and are served hot or cold. Lettuce is also used in a larger variety of dishes than in Western countries, contributing to a range of dishes including bean curd and meat dishes, soups and stir-frys plain or with other vegetables. Stem lettuce, widely consumed in China, is eaten either raw or cooked, the latter primarily in soups and stir-frys. Lettuce is also used as a primary ingredient in the preparation of lettuce soup.

Raw iceberg lettuce is 96% water, 3% carbohydrates, and contains negligible protein and fat (table). In a reference amount of {{convert|100|g}}, iceberg lettuce supplies 14 calories and is a rich source (20% or more of the Daily Value, DV) of vitamin K (20% DV), with no other micronutrients in significant content (table).

In lettuce varieties with dark green leaves, such as romaine (also called cos), vitamin A contents are appreciable due to the presence of the provitamin A compound, beta-carotene. Dark green varieties of lettuce also contain moderate amounts of calcium and iron. The edible spine and ribs of the lettuce plant supply dietary fiber, while micronutrients are contained in the leaf portion.

Food-borne pathogens that can survive on lettuce include Listeria monocytogenes, the causative agent of listeriosis, which multiplies in storage. However, despite high levels of bacteria being found on ready-to-eat lettuce products, a 2008 study found no incidents of food-borne illness related to listeriosis, possibly due to the product's short shelf life, indigenous microflora competing with the Listeria bacteria or inhibition of bacteria to cause listeriosis.{{cite journal|title=Precut prepackaged lettuce: a risk for listeriosis?|author1=Hanning, I.B. |author2=Johnson, M.G. |author3=Ricke, S.C |journal=Foodborne Pathogens and Disease|date=December 2008|volume=5|issue=6|pages=731–746|pmid=18847382|doi=10.1089/fpd.2008.0142}}

Other bacteria found on lettuce include Aeromonas species, which have not been linked to any outbreaks; Campylobacter species, which cause campylobacteriosis; and Yersinia intermedia and Yersinia kristensenii (species of Yersinia), which have been found mainly in lettuce.{{cite web|url=https://www.fda.gov/Food/ScienceResearch/ResearchAreas/SafePracticesforFoodProcesses/ucm091265.htm|archive-url=https://web.archive.org/web/20121109123857/https://www.fda.gov/Food/ScienceResearch/ResearchAreas/SafePracticesforFoodProcesses/ucm091265.htm|archive-date=2012-11-09|title=Chapter IV. Outbreaks Associated with Fresh and Fresh-Cut Produce. Incidence, Growth, and Survival of Pathogens in Fresh and Fresh-Cut Produce|publisher=US Food and Drug Administration|access-date=19 April 2012|work=Analysis and Evaluation of Preventive Control Measures for the Control and Reduction/Elimination of Microbial Hazards on Fresh and Fresh-Cut Produce|date=12 April 2012}} Salmonella bacteria, including the uncommon Salmonella braenderup type, have also caused outbreaks traced to contaminated lettuce.{{cite journal|title=Multiple outbreaks of Salmonella braenderup associated with consumption of iceberg lettuce|journal=International Journal of Environmental Health Research|volume=22|issue=2|date=April 2012|author1=Gajraj, Roger |author2=Pooransingh, Shalini |author3=Hawker, Jeremy |author4=Olowokure, Babatunde |pages=150–155|doi=10.1080/09603123.2011.613114|pmid=21916661|bibcode=2012IJEHR..22..150G |s2cid=27881973}} Viruses, including hepatitis A, calicivirus and a Norwalk-like strain, have been found in lettuce. The vegetable has also been linked to outbreaks of parasitic infestations, including Giardia lamblia.

Lettuce has been linked to numerous outbreaks of the bacteria E.coli O157:H7 and Shigella; the plants were most likely contaminated through contact with animal{{cite web|url=http://www.ext.colostate.edu/pubs/foodnut/09369.html|title=Preventing E. coli from Garden to Plate|publisher=Colorado State University|author1=Davis, J. G.|author2=Kendall, P.|access-date=26 March 2012|archive-url=https://web.archive.org/web/20120305133942/http://www.ext.colostate.edu/pubs/foodnut/09369.html|archive-date=5 March 2012|url-status=dead}} or human feces.{{cite journal|display-authors=3 |last1=Summerlin III |first1=HN |last2=Pola |first2=CC |last3=McLamore |first3=ES |last4=Gentry |first4=T |last5=Karthikeyan |first5=R |last6=Gomes |first6=CL |title=Prevalence of Escherichia coli and Antibiotic-Resistant Bacteria During Fresh Produce Production (Romaine Lettuce) Using Municipal Wastewater Effluents |journal=Front. Microbiol. |date=May 20, 2021 |volume=12 |issue=660047 |page=660047 |doi=10.3389/fmicb.2021.660047 |pmid=34093474 |pmc=8172605 |doi-access=free }} A 2007 study determined that the vacuum cooling method, especially prevalent in the California lettuce industry, increased the uptake and survival rates of E. coli O157:H7.{{cite journal|title=Impact of Vacuum Cooling on Escherichia coli O157:H7 Infiltration into Lettuce Tissue|journal=Applied and Environmental Microbiology |year=2008 |volume=74 |issue=10 |pages=3138–42 |pmid=18344328 |pmc=2394940 |doi=10.1128/AEM.02811-07 |last1=Li|first1=Haiping|last2=Tajkarimi|first2=Mehrdad|last3=Osburn|first3=Bennie I|bibcode=2008ApEnM..74.3138L|author-link3=Bennie Osburn}} Scientific experiments using treated municipal wastewater as irrigation for romaine lettuce have shown that the contamination levels of foliage, leachate, and soil with E. coli and bacteriophage AP205 (used by researchers as a surrogate for enteric viruses), respectively, were directly correlated with the presence of these organisms in the irrigation water.{{cite journal|display-authors=3 |last1=Summerlin III |first1=HN |last2=Pola |first2=CC |last3=Chamakura |first3=KR |last4=Young |first4=R |last5=Gentry |first5=T |last6=McLamore |first6=ES |last7=Karthikeyan |first7=R |last8=Gomes |first8=CL |title=Fate of enteric viruses during leafy greens (romaine lettuce) production using treated municipal wastewater and AP205 bacteriophage as a surrogate |journal= Journal of Environmental Science and Health, Part A|date=2021 |volume=566 |issue=10 |pages=1138–1144 |doi=10.1080/10934529.2021.1968231 |pmid=34427159|bibcode=2021JESHA..56.1138S |s2cid=237282172 }}

Due to the increase in food demand, the use of treated wastewater effluent for irrigation and animal or human excreta (i.e., manure or biosolids) as soil amendments is increasing.{{cite journal |last1=Mays |first1=C |last2=Garza |first2=GL |last3=Waite-Cusic |first3=J |last4=Radniecki |first4=TS |last5=Navab-Daneshmanda |first5=Tala |title=Impact of biosolids amendment and wastewater effluent irrigation on enteric antibiotic-resistant bacteria – a greenhouse study |journal=Water Res X |date=1 Dec 2021 |volume=13 |issue=100119 |page=100119 |doi=10.1016/j.wroa.2021.100119 |pmid=34585133 |pmc=8452883 |bibcode=2021WRX....1300119M }} As such, so are the outbreaks of food-borne illnesses. Due to the overuse of antibiotics in farming, the number of pathogens resistant to antibiotics is increasing,{{cite journal |last1=Xu |first1=C |last2=Kong |first2=L |last3=Liao |first3=Y |last4=Wu |first4=Q |last5=Liu |first5=H |last6=Wang |first6=X |title=Mini-Review: Antibiotic-Resistant Escherichia coli from Farm Animal-Associated Sources |journal=Antibiotics |date=Nov 2022 |volume=11 |issue=11 |page=1535 |doi=10.3390/antibiotics11111535 |pmid=36358190 |pmc=9686710|doi-access=free }} one of these being AR E.coli, which has been found on lettuce irrigated with wastewater.{{cite journal |last1=O'Flaherty |first1=E |last2=Solimini |first2=AG |last3=Pantanella |first3=F |last4=De Giusti |first4=M |last5=Cummins |first5=E |title=Human exposure to antibiotic resistant-Escherichia coli through irrigated lettuce |journal= Environment International|date=Jan 2019 |volume=122 |pages=270–280 |doi= 10.1016/j.envint.2018.11.022 |pmid=30449627 |doi-access=free |bibcode=2019EnInt.122..270O }}[https://reader.elsevier.com/reader/sd/pii/S016041201831643X?token=6585D28FDB16B77BA3788376DE943682C9ACD372BB9D47147E75615A28E1D9FDE92B07AE629981AED95FDED694DB104F&originRegion=us-east-1&originCreation=20230412164332 PDF]

Pathogens found on lettuce are not specific to lettuce (though some E. coli strains have affinity for Romaine). But, unlike other vegetables which tend to be cooked, lettuce is eaten raw, thus food-borne outbreaks associated with it are more frequent and affect a larger number of people.{{cite journal |last1=Gudda |first1=FO |last2=Waigi |first2=MG |last3=Odinga |first3=ES |last4=Yang |first4=B |last5=Carter |first5=L |last6=Gao |first6=Y |title=Antibiotic-contaminated wastewater irrigated vegetables pose resistance selection risks to the gut microbiome |journal= Environmental Pollution|date=Sep 2020 |volume=264 |pages=114752 |doi=10.1016/j.envpol.2020.114752 |pmid=32417582|bibcode=2020EPoll.26414752G |s2cid=218679107 }}

{{Reflist}}

• {{cite book

| editor1-last = Bradley

| editor1-first = Fern Marshall

| editor2-last = Ellis

| editor2-first = Barbara W.

| editor3-last = Martin

| editor3-first = Deborah L.

| year = 2009

| title = The Organic Gardener's Handbook of Natural Pest and Disease Control

| publisher = Rodale

| isbn = 978-1-60529-677-7

| url-access = registration

| url = https://archive.org/details/organicgardeners00brad_0

}}

• {{cite book

| last1 = Davey

| first1 = M. R.

| last2 = Anthony

| first2 = P.

| last3 = Van Hooff

| first3 = P.

| last4 = Power

| first4 = J. B.

| last5 = Lowe

| first5 = K. C.

| year = 2007

| chapter = Lettuce

| title = Transgenic Crops

| volume = 59

| series = Biotechnology in Agriculture and Forestry

| publisher = Springer

| isbn = 978-3-540-36752-9

}}

• {{cite book

| last1 = Katz

| first1 = Solomon H.

| last2 = Weaver

| first2 = Williams Woys

| year = 2003

| title = Encyclopedia of Food and Culture

| volume = 2

| publisher = Scribner

| isbn = 978-0-684-80565-8

}}

• {{cite book

| last = Weaver

| first = William Woys

| year = 1997

| title = Heirloom Vegetable Gardening: A Master Gardener's Guide to Planting, Seed Saving and Cultural History

| publisher = Henry Holt and Company

| isbn = 978-0-8050-4025-8

}}

{{portal|Food}}

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|voy=yes |commonscat= |author= |cookbook=yes|auto=1}}

{{Taxonbar|from=Q83193}}

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