Lettuce

Lettuce (Lactuca sativa) is an annual plant of the daisy family, Asteraceae. It is most often grown as a leaf vegetable, but sometimes for its stem and seeds. Lettuce is most often used for salads, although it is also seen in other kinds of food, such as soups, sandwiches and wraps; it can also be grilled.[3] One variety, the woju (莴苣), or asparagus lettuce (celtuce), is grown for its stems, which are eaten either raw or cooked. In addition to its main use as a leafy green, it has also gathered religious and medicinal significance over centuries of human consumption. Europe and North America originally dominated the market for lettuce, but by the late 20th century the consumption of lettuce had spread throughout the world. World production of lettuce and chicory for calendar year 2015 was 26.1 million tonnes, 56% of which came from China.[4]

Lettuce was first cultivated by the ancient Egyptians who turned it from a weed whose seeds were used to produce oil, into a food plant grown for its succulent leaves and oil-rich seeds. Lettuce spread to the Greeks and Romans, the latter of whom gave it the name lactuca, from which the English lettuce is ultimately derived. By 50 AD, many types were described, and lettuce appeared often in medieval writings, including several herbals. The 16th through 18th centuries saw the development of many varieties in Europe, and by the mid-18th century cultivars were described that can still be found in gardens.

Generally grown as a hardy annual, lettuce is easily cultivated, although it requires relatively low temperatures to prevent it from flowering quickly. It can be plagued by numerous nutrient deficiencies, as well as insect and mammal pests, and fungal and bacterial diseases. L. sativa crosses easily within the species and with some other species within the genus Lactuca. Although this trait can be a problem to home gardeners who attempt to save seeds, biologists have used it to broaden the gene pool of cultivated lettuce varieties.

Lettuce is a rich source of vitamin K and vitamin A, and a moderate source of folate and iron. Contaminated lettuce is often a source of bacterial, viral, and parasitic outbreaks in humans, including E. coli and Salmonella.

Lettuce
Iceberg lettuce in SB
An iceberg lettuce field in California
Scientific classification
Kingdom: Plantae
Clade: Angiosperms
Clade: Eudicots
Clade: Asterids
Order: Asterales
Family: Asteraceae
Genus: Lactuca
Species:
L. sativa
Binomial name
Lactuca sativa
Synonyms[1][2]

Taxonomy and etymology

Lactuca sativa seeds
L. sativa seeds

Lactuca sativa is a member of the Lactuca (lettuce) genus and the Asteraceae (sunflower or aster) family.[5] The species was first described in 1753 by Carl Linnaeus in the second volume of his Species Plantarum.[6] Synonyms for L. sativa include Lactuca scariola var. sativa,[1] L. scariola var. integrata and L. scariola var. integrifolia.[7] L. scariola is itself a synonym for L. serriola, the common wild or prickly lettuce.[2] L. sativa also has many identified taxonomic groups, subspecies and varieties, which delineate the various cultivar groups of domesticated lettuce.[8] 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.[9]

The Romans referred to lettuce as lactuca (lac meaning milk in Latin), an allusion to the white substance, now called latex, exuded by cut stems.[10] This word has become the genus name, while sativa (meaning "sown" or "cultivated") was added to create the species name.[11] The current word lettuce, originally from Middle English, came from the Old French letues or laitues, which derived from the Roman name.[12] The name romaine came from that type's use in the Roman papal gardens, while cos, another term for romaine lettuce, came from the earliest European seeds of the type from the Greek island of Cos, a center of lettuce farming in the Byzantine period.[13]

Description

Lactuca sativa, botersla
Lettuce flowers
Kropsla vruchten (Lactuca sativa fruits)
Mature lettuce inflorescence in fruit

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 15 to 30 cm (6 to 12 in).[14] The leaves are colorful, mainly in the green and red color spectrums, with some variegated varieties.[15] There are also a few varieties with yellow, gold or blue-teal leaves.[16] 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.[15] 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.[16]

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.[17] Once plants move past the edible stage, they develop flower stalks up to 1 m (3 ft 3 in) high with small yellow blossoms.[18] 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.[16][19] 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.[1]

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.[20] 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 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.[21]

History

Romaine
Romaine lettuce, a descendant of some of the earliest cultivated lettuce

Lettuce was first cultivated in ancient Egypt for the production of oil from its seeds. This plant was probably selectively bred by the Egyptians into a plant grown for its edible leaves,[22] with evidence of its cultivation appearing as early as 2680 BC.[10] Lettuce was considered a sacred plant of the reproduction god Min, and it was carried during his festivals and placed near his images. The plant was thought to help the god "perform the sexual act untiringly."[23] 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 75 cm (30 in) 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. Circa 50 AD, Roman agriculturalist Columella described several lettuce varieties – some of which may have been ancestors of today's lettuces.[10]

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.[13] Lettuce was first brought to the Americas from Europe by Christopher Columbus in the late 15th century.[24][25] 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.[26]

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.[27] 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.[28]

Lettuce is very 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 was done 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.[29] 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.[30]

Cultivation

Park Lane Nurseries - geograph.org.uk - 583201
A lettuce-growing facility in the United Kingdom

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.[26] 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 20 to 36 cm (7.9 to 14.2 in) apart, in the garden after developing several leaves. Lettuce spaced further 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.[18]

Planche Lactuca sativa
A transplanted bed of lettuce in a polytunnel

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 24 °C (75 °F); cool temperatures prompt better performance, with 16 to 18 °C (61 to 64 °F) being preferred and as low as 7 °C (45 °F) being tolerated.[31] Plants in hot areas that are provided partial shade during the hottest part of the day will bolt more slowly. Temperatures above 27 °C (81 °F) will generally result in poor or non-existent germination of lettuce seeds.[31] After harvest, lettuce lasts the longest when kept at 0 °C (32 °F) and 96 percent humidity. Lettuce quickly degrades when stored with fruit such as apples, pears and bananas that release the ripening agent ethylene gas. 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.[32]

Lettuce varieties will cross with each other, making spacing of 1.5 to 6 m (60 to 240 in) 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.[18] 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.[33] Seeds keep best when stored in cool conditions, and, unless stored cryogenically, remain viable the longest when stored at −20 °C (−4 °F); they are relatively short lived in storage.[1] 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.[34]

Cultivars (varieties)

Lettuce mix
A selection of lettuce cultivars

There are several types of lettuce, but three (leaf, head and cos or romaine) are the most common.[31] There are seven main cultivar groups of lettuce, each including many varieties:

  • Leaf – Also known as looseleaf, cutting or bunching lettuce,[35] this type has loosely bunched leaves and is the most widely planted. It is used mainly for salads.[32]
  • Romaine/Cos – Used mainly for salads and sandwiches, this type forms long, upright heads.[32] This is the most often used lettuce in Caesar salads.[24]
  • Iceberg/Crisphead – The most popular type in the United States, it is very heat-sensitive and was originally adapted for growth in the northern United States. It ships well, but is low in flavor and nutritional content, being composed of even more water than other lettuce types.[32]
  • Butterhead – Also known as Boston or Bibb lettuce,[35] and traditional in the UK as "round lettuce",[36] this type is a head lettuce with a loose arrangement of leaves, known for its sweet flavor and tender texture.[32]
Yangzhou - supermarket - woju - P1070028
The lettuce variety celtuce is grown for its stem, used in Chinese cooking
  • 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.[35]
  • 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.[32]
  • 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.[37]

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.[38]

Cultivation problems

Starr 081031-0356 Lactuca sativa
A lettuce surrounded by weeds, which have crowded it to the point of bolting

Soil nutrient deficiencies can cause a variety of plant problems that range from malformed plants to a lack of head growth.[31] 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.[39] Mammals, including rabbits and groundhogs, also eat the plants.[40] 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.[41]

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.[40] Crowding lettuce tends to attract pests and diseases.[18] 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.[42] Herbicides are often used to control weeds in commercial production. However, this has led to the development of herbicide-resistant weeds and prompted environmental and health concerns.[20]

Production

Lettuce production
(millions of tonnes)
Country 2015
 China
14.6
 United States
3.8
 India
1.1
 Spain
0.9
 Italy
0.6
World
26.1
Source: UN Food & Agriculture Organization[4]

In 2015, world production of lettuce (report combined with chicory) was 26.1 million tonnes, with China alone producing 14.6 million tonnes or 56% of the world total (table).

Lettuce is the only member of the genus Lactuca to be grown commercially.[43] Although China is the top world producer of lettuce, the majority of the crop is consumed domestically. Spain is the world's largest exporter of lettuce, with the US ranking second.[27]

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.[44] Stem lettuce was first developed in China, and remains primarily cultivated in that country.[45]

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.[46][47][48]

In the United States in 2013, California (71%) and Arizona (29%) produced nearly all of the country's fresh head and leaf lettuce, with head lettuce yielding $9400 of value per acre and leaf lettuce $8000 per acre.[47]

Culinary use

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.[10] 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.[22] Most lettuce is used in salads, either alone or with other greens, vegetables, meats and cheeses. Romaine lettuce is often used for Caesar salads, with a dressing that includes anchovies and eggs. Lettuce leaves can also be found in soups, sandwiches and wraps, while the stems are eaten both raw and cooked.[11] The consumption of lettuce in China developed differently from in Western countries, due to health risks and cultural aversion to eating raw leaves. In that country, "salads" were created from cooked vegetables and served hot or cold. Lettuce was 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.[45] Lettuce is also used as a primary ingredient in the preparation of lettuce soup.

Nutritional content

Lettuce (butterhead)
Nutritional value per 100 g (3.5 oz)
Energy55 kJ (13 kcal)
2.23 g
Sugars0.94
Dietary fiber1.1 g
0.22 g
1.35 g
VitaminsQuantity %DV
Vitamin A equiv.
21%
166 μg
18%
1987 μg
1223 μg
Thiamine (B1)
5%
0.057 mg
Riboflavin (B2)
5%
0.062 mg
Pantothenic acid (B5)
3%
0.15 mg
Vitamin B6
6%
0.082 mg
Folate (B9)
18%
73 μg
Vitamin C
4%
3.7 mg
Vitamin E
1%
0.18 mg
Vitamin K
97%
102.3 μg
MineralsQuantity %DV
Calcium
4%
35 mg
Iron
10%
1.24 mg
Magnesium
4%
13 mg
Manganese
9%
0.179 mg
Phosphorus
5%
33 mg
Potassium
5%
238 mg
Sodium
0%
5 mg
Zinc
2%
0.2 mg
Other constituentsQuantity
Water95.63 g

Percentages are roughly approximated using US recommendations for adults.
Source: USDA Nutrient Database

Depending on the variety, lettuce is an excellent source (20% of the Daily Value, DV, or higher) of vitamin K (97% DV) and vitamin A (21% DV) (table), with higher concentrations of the provitamin A compound, beta-carotene, found in darker green lettuces, such as Romaine.[32] With the exception of the iceberg variety, lettuce is also a good source (10-19% DV) of folate and iron (table).[32]

Food-borne illness

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 incidences 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.[49]

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.[50] 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 feces.[51] 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.[52] Salmonella bacteria, including the uncommon Salmonella braenderup type, have also caused outbreaks traced to contaminated lettuce.[53] 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.[50]

Religious and medicinal lore

In addition to its usual purpose as an edible leafy vegetable, lettuce has had a number of uses in ancient (and even some more modern) times as a medicinal herb and religious symbol. For example, ancient Egyptians thought lettuce to be a symbol of sexual prowess[44] and a promoter of love and childbearing in women. The Romans likewise claimed that it increased sexual potency.[54] In contrast, the ancient Greeks connected the plant with male impotency,[10] and served it during funerals (probably due to its role in the myth of Adonis' death), and British women in the 19th century believed it would cause infertility and sterility. Lettuce has mild narcotic properties; it was called "sleepwort" by the Anglo-Saxons because of this attribute, although the cultivated L. sativa has lower levels of the narcotic than its wild cousins.[54] This narcotic effect is a property of two sesquiterpene lactones which are found in the white liquid (latex) in the stems of lettuce,[30] called lactucarium or "lettuce opium".

Lettuce is also eaten as part of the Jewish Passover Seder, where it is considered the optimal choice for use as the bitter herb, which is eaten together with the matzah.

Some American settlers claimed that smallpox could be prevented through the ingestion of lettuce,[54] and an Iranian belief suggested consumption of the seeds when afflicted with typhoid.[55] Folk medicine has also claimed it as a treatment for pain, rheumatism, tension and nervousness, coughs and insanity; scientific evidence of these benefits in humans has not been found. The religious ties of lettuce continue into the present day among the Yazidi people of northern Iraq, who have a religious prohibition against eating the plant.[56]

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  46. ^ Fulmer, Melinda (19 August 2002). "Lettuce Grows Into A Processed Food". Los Angeles Times. Archived from the original on 18 December 2013. Retrieved 30 June 2012.
  47. ^ a b "Lettuce". Agricultural Marketing Resource Center, Iowa State University. May 2015. Archived from the original on 13 October 2016. Retrieved 7 October 2016.
  48. ^ Charles, Dan; Aubrey, Allison (12 July 2016). "As Bagged Salad Kits Boom, Americans Eat More Greens". National Public Radio. Archived from the original on 3 April 2018. Retrieved 5 April 2018.
  49. ^ Hanning, I.B.; Johnson, M.G.; Ricke, S.C (December 2008). "Precut prepackaged lettuce: a risk for listeriosis?". Foodborne Pathogens and Disease. 5 (6): 731–746. doi:10.1089/fpd.2008.0142. PMID 18847382.
  50. ^ a b "Chapter IV. Outbreaks Associated with Fresh and Fresh-Cut Produce. Incidence, Growth, and Survival of Pathogens in Fresh and Fresh-Cut Produce". Analysis and Evaluation of Preventive Control Measures for the Control and Reduction/Elimination of Microbial Hazards on Fresh and Fresh-Cut Produce. US Food and Drug Administration. 12 April 2012. Archived from the original on 9 November 2012. Retrieved 19 April 2012.
  51. ^ Davis, J. G.; Kendall, P. "Preventing E. coli from Garden to Plate". Colorado State University. Archived from the original on 5 March 2012. Retrieved 26 March 2012.
  52. ^ Li, Haiping; Tajkarimi, Mehrdad; Osburn, Bennie I (2008). "Impact of Vacuum Cooling on Escherichia coli O157:H7 Infiltration into Lettuce Tissue". Applied and Environmental Microbiology. 74 (10): 3138–42. doi:10.1128/AEM.02811-07. PMC 2394940. PMID 18344328.
  53. ^ Gajraj, Roger; Pooransingh, Shalini; Hawker, Jeremy; Olowokure, Babatunde (April 2012). "Multiple outbreaks of Salmonella braenderup associated with consumption of iceberg lettuce". International Journal of Environmental Health Research. 22 (2): 150–155. doi:10.1080/09603123.2011.613114. PMID 21916661.
  54. ^ a b c Watts, Donald (2007). Dictionary of Plant Lore. Academic Press. p. 226. ISBN 0-12-374086-X.
  55. ^ Duke, James A.; Duke, Peggy-Ann K.; DuCellie, Judith L. (2007). Duke's Handbook of Medicinal Plants of the Bible. CRC Press. p. 232. ISBN 0-8493-8202-5. Archived from the original on 19 May 2016. Retrieved 10 January 2016.
  56. ^ MacFarquhar, Neil (3 January 2003). "Bashiqa Journal: A Sect Shuns Lettuce and Gives the Devil His Due". The New York Times. Retrieved 23 March 2012.

Cited literature

  • Bradley, Fern Marshall; Ellis, Barbara W.; Martin, Deborah L., eds. (2009). The Organic Gardener's Handbook of Natural Pest and Disease Control. Rodale. ISBN 978-1-60529-677-7.
  • Davey, M. R.; Anthony, P.; Van Hooff, P.; Power, J. B.; Lowe,, K. C. (2007). "Lettuce". Transgenic Crops. Biotechnology in Agriculture and Forestry. Volume 59. Springer. ISBN 978-3-540-36752-9.
  • Katz, Solomon H.; Weaver, Williams Woys (2003). Encyclopedia of Food and Culture. Volume 2. Scribner. ISBN 978-0-684-80565-8.
  • Weaver, Williams Woys (1997). Heirloom Vegetable Gardening: A Master Gardener's Guide to Planting, Seed Saving and Cultural History. Henry Holt and Company. ISBN 978-0-8050-4025-8.

External links

BLT

A BLT is a type of sandwich, named for the initials of its primary ingredients, bacon, lettuce and tomato. It can be made with varying recipes according to personal preference. Simple variants include using different types of lettuce, toasting or not, or adding mayonnaise. More pronounced variants can include using turkey bacon or tofu in place of bacon, or removing the lettuce entirely.

The combination of ingredients on a sandwich dates back to the early 1900s, though it didn't achieve widespread popularity until after World War II, when the ingredients became more readily available year-round. Referencing the sandwich by its initials rather than naming the ingredients in full did not become common until the 1970s. The BLT has been ranked as the second most popular sandwich in the US and as the UK's favourite sandwich, and is frequently referenced or depicted in media and culture.

Big Mac

The Big Mac is a hamburger sold by international fast food restaurant chain McDonald's. It was introduced in the Greater Pittsburgh area, United States, in 1967 and nationwide in 1968. It is one of the company's flagship products.

Chalupa

A chalupa (Spanish pronunciation: [tʃaˈlupa]) is a specialty dish of south-central Mexico, including the states of Puebla, Guerrero, and Oaxaca. Chalupas are made by pressing a thin layer of masa dough around the outside of a small mold, in the process creating a concave container resembling the boat of the same name, and then deep frying the result to produce crisp, shallow corn cups. These are filled with various ingredients such as shredded chicken, pork, chopped onion, chipotle pepper, red salsa, and/or green salsa. They can in many cases resemble tostadas since both are made of a fried or baked masa-based dough.Traditional chalupas, as found in Cholula, Puebla, are small, thick, boat-shaped fried masa topped only with salsa, cheese and shredded lettuce. Other regions in Mexico add variations, which can include chorizo, pork, shredded chicken, or re-fried beans, in addition to the classic cheese, salsa, and lettuce toppings. In other instances, the fried masa shape is round, resembling a tostada, with traditional chalupa toppings.The widespread popularity of chalupas across Mexico has also influenced Mexican-style restaurant fare in the neighboring United States. Among notable examples in that country is the Taco Bell version, which unlike like its Mexican version, is a thick, fried tortilla shell filled with ground beef, sour cream, cheese, tomatoes, and shredded lettuce. More closely resembling a taco, the Taco Bell version of the chalupa may be termed a rather distant relative of the Mexican original.

Club sandwich

A club sandwich, also called a clubhouse sandwich, is a sandwich of bread (traditionally toasted), sliced cooked poultry, ham or fried bacon, lettuce, tomato, and mayonnaise.

It is often cut into quarters or halves and held together by cocktail sticks. Modern versions frequently have two layers which are separated by an additional slice of bread.

Cobb salad

The Cobb salad is a main-dish American garden salad typically made with chopped salad greens (iceberg lettuce, watercress, endives and romaine lettuce), tomato, crisp bacon, boiled, grilled or roasted (but not fried) chicken breast, hard-boiled eggs, avocado, chives, Roquefort cheese, and red-wine vinaigrette.

Eruca sativa

Arugula (American English) or rocket (British English) (Eruca sativa; syns. E. vesicaria subsp. sativa (Miller) Thell., Brassica eruca L.) is an edible annual plant in the family Brassicaceae used as a leaf vegetable for its fresh, tart, bitter, and peppery flavor. Other common names include garden rocket, (British, Australian, South African, Irish and New Zealand English), and eruca. Some additional names are "rocket salad", "rucola", "rucoli", "rugula", "colewort", and "roquette". Eruca sativa, which is widely popular as a salad vegetable, is a species of Eruca native to the Mediterranean region, from Morocco and Portugal in the west to Syria, Lebanon, and Turkey in the east.Eruca sativa grows 20–100 centimetres (8–39 in) in height. The pinnate leaves have four to ten small, deep, lateral lobes and a large terminal lobe. The flowers are 2–4 cm (0.8–1.6 in) in diameter, arranged in a corymb in typical Brassicaceae fashion, with creamy white petals veined in purple, and having yellow stamens; the sepals are shed soon after the flower opens. The fruit is a siliqua (pod) 12–35 millimetres (0.5–1.4 in) long with an apical beak, and containing several seeds (which are edible). The species has a chromosome number of 2n = 22.

Korean cuisine

Korean cuisine is the customary cooking traditions and practices of the culinary arts of Korea.

Korean cuisine has evolved through centuries of social and political change. Originating from ancient agricultural and nomadic traditions in Korea and southern Manchuria, Korean cuisine has evolved through a complex interaction of the natural environment and different cultural trends.Korean cuisine is largely based on rice, vegetables, and meats. Traditional Korean meals are named for the number of side dishes (반찬; 飯饌; banchan) that accompany steam-cooked short-grain rice. Kimchi is served at nearly every meal. Commonly used ingredients include sesame oil, doenjang (fermented bean paste), soy sauce, salt, garlic, ginger, pepper flakes, gochujang (fermented red chili paste) and napa cabbage.

Ingredients and dishes vary by province. Many regional dishes have become national, and dishes that were once regional have proliferated in different variations across the country. Korean royal court cuisine once brought all of the unique regional specialties together for the royal family. Foods are regulated by Korean cultural etiquette.

Lactuca

Lactuca, commonly known as lettuce, is a genus of flowering plants in the daisy family, Asteraceae. The genus includes at least 50 species, distributed worldwide, but mainly in temperate Eurasia.

Its best-known representative is the garden lettuce (Lactuca sativa), with its many varieties. "Wild lettuce" commonly refers to the wild-growing relatives of common garden lettuce. Many species are common weeds. Lactuca species are diverse and take a wide variety of forms. They are annuals, biennials, perennials, or shrubs. Their flower heads have yellow, blue, or white ray florets. Some species are bitter-tasting.

Most wild lettuces are xerophytes, adapted to dry habitat types. Some occur in more moist areas, such as the mountains of central Africa.

Lactuca serriola

Lactuca serriola, also called prickly lettuce, milk thistle (not to be confused with Silybum marianum, also called milk thistle) compass plant, and scarole, is an annual or biennial plant in the dandelion tribe within the daisy family. It has a slightly fetid odor and is commonly considered a weed of orchards, roadsides and field crops. It is the closest wild relative of cultivated lettuce (Lactuca sativa L.).

Lactuca serriola is known as the compass plant because in the Sun the upper leaves twist round to hold their margins upright.Lactuca serriola is native to Europe, Asia, and north Africa, and has become naturalized elsewhere.

Lactuca virosa

Lactuca virosa is a plant in the Lactuca (lettuce) genus, ingested often for its mild analgesic and sedative effects. It is related to common lettuce (L. sativa), and is often called wild lettuce, bitter lettuce, laitue vireuse, opium lettuce, poisonous lettuce, tall lettuce, great lettuce or rakutu-karyumu-so.

Lettuce sandwich

A lettuce sandwich is a wrap with lettuce substituted for the bread, or a sandwich with a filling consisting primarily of lettuce.

It should not be confused with other sandwiches that use lettuce as one of many ingredients, such as the BLT sandwich or the tomato and lettuce sandwich. The lettuce sandwich has a long history in both the United States and the United Kingdom. It has been used as a metaphor to represent things like mundanity, weakness and poverty.

List of salads

Salad is any of a wide variety of dishes including: green salads; vegetable salads; salads of pasta, legumes, or grains; mixed salads incorporating meat, poultry, or seafood; and fruit salads. They often include vegetables and/or fruits.

Pistia

Pistia is a genus of aquatic plant in the arum family, Araceae. The single species it comprises, Pistia stratiotes, is often called water cabbage, water lettuce, Nile cabbage, or shellflower. Its native distribution is uncertain, but probably pantropical; it was first discovered from the Nile near Lake Victoria in Africa. It is now present, either naturally or through human introduction, in nearly all tropical and subtropical fresh waterways and considered an invasive species as well as a mosquito breeding habitat. The genus name is derived from the Greek word πιστός (pistos), meaning "water," and refers to the aquatic nature of the plants.

Prawn roll

A prawn roll is a sandwich item available in areas of Australia, where prawn fishing is a major industry. They typically are made using a soft white roll approximately six inches (15 cm) long, stuffed with a dozen or more peeled prawns, lettuce and remoulade, Thousand Island or cocktail-style sauce.

Romaine lettuce

Romaine or cos lettuce (Lactuca sativa L. var. longifolia) is a variety of lettuce that grows in a tall head of sturdy dark green leaves with firm ribs down their centers. Unlike most lettuces, it is tolerant of heat. In North America, romaine is sold as whole heads or as “hearts” that have had the outer leaves removed and are often packaged together.

Commercially sold romaine lettuce has historically been the subject of product warnings by both U.S. and Canadian health authorities warning that consumer supplies can become adulterated with or host pathogenic E. coli bacteria. Cattle can harbor the bacteria without ill effects, and be asymptomatic carriers of the bacterium. Lettuce becomes contaminated with the bacterium as the result of cattle manure being used to fertilize crop fields, or the proximity of cattle pastures and feedlots to water sources used to irrigate crops.

Salad

A salad is a dish consisting of a mixture of small pieces of food, usually vegetables. However, different varieties of salad may contain virtually any type of ready-to-eat food. Salads are typically served at room temperature or chilled, with notable exceptions such as south German potato salad which is served warm.

Garden salads use a base of leafy greens such as lettuce, arugula/rocket, kale or spinach; they are common enough that the word salad alone often refers specifically to garden salads. Other types include bean salad, tuna salad, fattoush, Greek salad (vegetable based, but without leafy greens), and sōmen salad (a noodle-based salad). The sauce used to flavor a salad is commonly called a salad dressing; most salad dressings are based on either a mixture of oil and vinegar or a fermented milk product like kefir.

Salads may be served at any point during a meal:

Appetizer salads—light, smaller-portion salads served as the first course of the meal.

Side salads—to accompany the main course as a side dish.

Main course salads—usually containing a portion of a high-protein food, such as meat, fish, eggs, legumes, or cheese.

Dessert salads—sweet versions containing fruit, gelatin, sweeteners or whipped cream.

Sea lettuce

The sea lettuces comprise the genus Ulva, a group of edible green algae that is widely distributed along the coasts of the world's oceans. The type species within the genus Ulva is Ulva lactuca, lactuca being Latin for "lettuce". The genus also includes the species previously classified under the genus Enteromorpha, the former members of which are known under the common name green nori.

Slug and Lettuce

Slug and Lettuce is a chain of bars that operate in the United Kingdom, with a large number located in London and South East England. As of 2017, there are a total of 70 outlets. Hugh Corbett opened the first Slug and Lettuce in Islington in 1984. He attempted to enhance the public house environment, at a time when standards were often low.

The bars are designed for a youthful clientele, and aim to attract an equal number of men and women with "female friendly" designs. The chain has remained relevant by continually re-inventing itself for the contemporary marketplace. The chain has gone through a number of owners throughout its history, and is currently owned by the Stonegate Pub Company, based in Luton, Bedfordshire.

Valerianella locusta

Valerianella locusta is a small annual plant that is eaten as a leaf vegetable. It has a characteristic nutty flavour, dark green colour, and soft texture, and is popularly served as salad greens. Common names include corn salad, common cornsalad, lamb's lettuce, mâche (), fetticus, feldsalat, nut lettuce, field salad, and rapunzel. In restaurants that feature French cooking, it may be called doucette or raiponce, as an alternative to mâche, by which it is best known. In German-speaking Switzerland it is known as Nüsslisalat or Nüssler, terms that have been borrowed by the area's many English-speakers. It is typically served as a salad with chopped hard-boiled eggs and crumbled bacon.

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