Lettuce (''Lactuca sativa'') is an
annual plant
An annual plant is a plant that completes its life cycle, from germination to the production of seeds, within one growing season, and then dies. The length of growing seasons and period in which they take place vary according to geographical ...
of the family
Asteraceae
The family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae w ...
. It is most often grown as a leaf vegetable, but sometimes for its stem and seeds. Lettuce is most often used for
salad
A salad is a dish consisting of mixed, mostly natural ingredients with at least one raw ingredient. They are typically served at room temperature or chilled, though some can be served warm. Condiments and salad dressings, which exist in a va ...
s, although it is also seen in other kinds of food, such as soups, sandwiches and wraps; it can also be grilled. One variety,
celtuce
Celtuce () (''Lactuca sativa'' var. ''augustana'',Masatoshi Yamaguchi Caroline Foley ''angustata'', or ''asparagina''), also called stem lettuce, celery lettuce, asparagus lettuce, or Chinese lettuce, is a cultivar of lettuce grown primarily ...
(asparagus lettuce), 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
Common chicory ('' Cichorium intybus'') is a somewhat woody, perennial herbaceous plant of the family Asteraceae, usually with bright blue flowers, rarely white or pink. Native to the Old World, it has been introduced to North America and Austra ...
was 27 million
tonnes
The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United States ...
, 56percent of which came from China.
Lettuce was originally farmed by the
ancient Egyptians, who transformed it from a plant whose seeds were used to obtain oil into an important food crop raised for its succulent leaves and oil-rich seeds. Lettuce spread to the Greeks and Romans; the latter gave it the name , from which the English ''lettuce'' is derived. By 50 AD, many types were described, and lettuce appeared often in medieval writings, including several
herbal
A herbal is a book containing the names and descriptions of plants, usually with information on their medicinal, tonic, culinary, toxic, hallucinatory, aromatic, or magical powers, and the legends associated with them.Arber, p. 14. A herbal m ...
s. The 16th through 18th centuries saw the development of many
varieties
Variety may refer to:
Arts and entertainment Entertainment formats
* Variety (radio)
* Variety show, in theater and television
Films
* ''Variety'' (1925 film), a German silent film directed by Ewald Andre Dupont
* ''Variety'' (1935 film), ...
in Europe, and by the mid-18th century, cultivars were described that can still be found in modern gardens.
Generally grown as a
hardy annual
Annual may refer to:
* Annual publication, periodical publications appearing regularly once per year
**Yearbook
** Literary annual
* Annual plant
* Annual report
* Annual giving
* Annual, Morocco, a settlement in northeastern Morocco
* Annuals (b ...
, lettuce is easily cultivated, although it requires relatively low temperatures to prevent it from flowering quickly. It can be plagued by numerous
nutrient deficiencies
Malnutrition occurs when an organism gets too few or too many nutrients, resulting in health problems. Specifically, it is "a deficiency, excess, or imbalance of energy, protein and other nutrients" which adversely affects the body's tissues ...
, as well as insect and mammal pests, and fungal and bacterial diseases. ''L. sativa''
crosses
Crosses may refer to:
* Cross, the symbol
Geography
* Crosses, Cher, a French municipality
* Crosses, Arkansas, a small community located in the Ozarks of north west Arkansas
Language
* Crosses, a truce term used in East Anglia and Lincolnshire ...
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
The gene pool is the set of all genes, or genetic information, in any population, usually of a particular species.
Description
A large gene pool indicates extensive genetic diversity, which is associated with robust populations that can surv ...
of cultivated lettuce varieties.
Lettuce is a rich source of
vitamin K
Vitamin K refers to structurally similar, fat-soluble vitamers found in foods and marketed as dietary supplements. The human body requires vitamin K for post-synthesis modification of certain proteins that are required for blood coagulation ...
and
vitamin A
Vitamin A is a fat-soluble vitamin and an essential nutrient for humans. It is a group of organic compounds that includes retinol, retinal (also known as retinaldehyde), retinoic acid, and several provitamin A carotenoids (most notably bet ...
, and a moderate source of
folate
Folate, also known as vitamin B9 and folacin, is one of the B vitamins. Manufactured folic acid, which is converted into folate by the body, is used as a dietary supplement and in food fortification as it is more stable during processing and ...
and
iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
. Contaminated lettuce is often a source of bacterial, viral, and parasitic outbreaks in humans, including ''
E. coli
''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...
'' and ''
Salmonella
''Salmonella'' is a genus of rod-shaped (bacillus) Gram-negative bacteria of the family Enterobacteriaceae. The two species of ''Salmonella'' are ''Salmonella enterica'' and ''Salmonella bongori''. ''S. enterica'' is the type species and is fur ...
''.
Taxonomy and etymology
![Lactuca sativa seeds](https://upload.wikimedia.org/wikipedia/commons/c/cc/Lactuca_sativa_seeds.jpg)
''Lactuca sativa'' is a member of the ''
Lactuca
''Lactuca'', commonly known as lettuce, is a genus of flowering plants in the family Asteraceae. The genus includes at least 50 species, distributed worldwide, but mainly in temperate Eurasia.
Its best-known representative is the garden lettuce ...
'' (lettuce) genus and the
Asteraceae
The family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae w ...
(
sunflower
The common sunflower (''Helianthus annuus'') is a large annual forb of the genus ''Helianthus'' grown as a crop for its edible oily seeds. Apart from cooking oil production, it is also used as livestock forage (as a meal or a silage plant), as ...
or
aster
Aster or ASTER may refer to:
Biology
* ''Aster'' (genus), a genus of flowering plants
** List of ''Aster'' synonyms, other genera formerly included in ''Aster'' and still called asters in English
* Aster (cell biology), a cellular structure shap ...
) family. The species was first described in 1753 by
Carl Linnaeus
Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...
in the second volume of his ''
Species Plantarum
' (Latin for "The Species of Plants") is a book by Carl Linnaeus, originally published in 1753, which lists every species of plant known at the time, classified into genera. It is the first work to consistently apply binomial names and was the ...
''. Synonyms for ''L. sativa'' include ''Lactuca scariola'' ''sativa'',
''L. scariola'' ''integrata'' and ''L. scariola'' ''integrifolia''. ''L. scariola'' is itself a
synonym
A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...
for ''
L. serriola'', the common wild or prickly lettuce.
''L. sativa'' also has many identified taxonomic
groups
A group is a number of persons or things that are located, gathered, or classed together.
Groups of people
* Cultural group, a group whose members share the same cultural identity
* Ethnic group, a group whose members share the same ethnic iden ...
,
subspecies
In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...
and
varieties
Variety may refer to:
Arts and entertainment Entertainment formats
* Variety (radio)
* Variety show, in theater and television
Films
* ''Variety'' (1925 film), a German silent film directed by Ewald Andre Dupont
* ''Variety'' (1935 film), ...
, which delineate the various
cultivar group
A Group (previously cultivar-groupInternational Code of Nomenclature for Cultivated Plants, 4th edition (1969), 5th edition (1980) and 6th edition (1995)) is a formal category in the ''International Code of Nomenclature for Cultivated Plants'' ('' ...
s of domesticated lettuce. Lettuce is closely related to several ''Lactuca'' species from southwest Asia; the closest relationship is to ''L. serriola'', an aggressive
weed
A weed is a plant considered undesirable in a particular situation, "a plant in the wrong place", or a plant growing where it is not wanted.Harlan, J. R., & deWet, J. M. (1965). Some thoughts about weeds. ''Economic botany'', ''19''(1), 16-24. ...
common in temperate and subtropical zones in much of the world.
The Romans referred to lettuce as ( meaning "dairy" in
Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
), an allusion to the white substance,
latex
Latex is an emulsion (stable dispersion) of polymer microparticles in water. Latexes are found in nature, but synthetic latexes are common as well.
In nature, latex is found as a milky fluid found in 10% of all flowering plants (angiosperms ...
, exuded by cut stems.
The name ''Lactuca'' has become the genus name, while (meaning "sown" or "cultivated") was added to create the species name.
[Katz and Weaver, p. 376.] The current word ''lettuce'', originally from
Middle English
Middle English (abbreviated to ME) is a form of the English language that was spoken after the Norman conquest of 1066, until the late 15th century. The English language underwent distinct variations and developments following the Old English p ...
, came from the
Old French
Old French (, , ; Modern French: ) was the language spoken in most of the northern half of France from approximately the 8th to the 14th centuries. Rather than a unified language, Old French was a linkage of Romance dialects, mutually intelligib ...
or , which derived from the Roman name. The name ''romaine'' came from the variety of lettuce grown in the Roman papal gardens, while ''cos'', another term for
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, ...
, came from the earliest European seeds of the type from the Greek island of
Kos
Kos or Cos (; el, Κως ) is a Greek island, part of the Dodecanese island chain in the southeastern Aegean Sea. Kos is the third largest island of the Dodecanese by area, after Rhodes and Karpathos; it has a population of 36,986 (2021 census), ...
, a center of lettuce farming in the
Byzantine period
The Byzantine Empire, also referred to as the Eastern Roman Empire or Byzantium, was the continuation of the Roman Empire primarily in its eastern provinces during Late Antiquity and the Middle Ages, when its capital city was Constantinopl ...
.
[Weaver, p. 172.]
Description
![Kropsla vruchten (Lactuca sativa fruits)](https://upload.wikimedia.org/wikipedia/commons/3/35/Kropsla_vruchten_%28Lactuca_sativa_fruits%29.jpg)
Lettuce's native range spreads from the
Mediterranean
The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the e ...
to
Siberia
Siberia ( ; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part of ...
, although it has been transported to almost all areas of the world. Plants generally have a height and spread of . The leaves are colorful, mainly in the green and red color spectrums, with some
variegated
Variegation is the appearance of differently coloured zones in the leaves and sometimes the stems and fruit of plants. Species with variegated individuals are sometimes found in the understory of tropical rainforests, and this habitat is the s ...
varieties.
There are also a few varieties with yellow, gold or blue-teal leaves.
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.
Lettuce plants have a root system that includes a main
taproot
A taproot is a large, central, and dominant root from which other roots sprout laterally. Typically a taproot is somewhat straight and very thick, is tapering in shape, and grows directly downward. In some plants, such as the carrot, the taproo ...
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.
Once plants move past the edible stage, they develop flower stalks up to high with small yellow blossoms.
Like other members of the tribe
Cichorieae
The Cichorieae (also called Lactuceae) are a tribe in the plant family Asteraceae that includes 93 genera, more than 1,600 sexually reproductive species and more than 7,000 Apomixis, apomictic species. They are found primarily in temperate region ...
, lettuce
inflorescence
An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Morphologically, it is the modified part of the shoot of seed plants where flowers are formed o ...
s (also known as
flower heads
A pseudanthium (Greek for "false flower"; ) is an inflorescence that resembles a flower. The word is sometimes used for other structures that are neither a true flower nor a true inflorescence. Examples of pseudanthia include flower heads, compos ...
or capitula) are composed of multiple
floret
This glossary of botanical terms is a list of definitions of terms and concepts relevant to botany and plants in general. Terms of plant morphology are included here as well as at the more specific Glossary of plant morphology and Glossary o ...
s, 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 A ligule (from "strap", variant of ''lingula'', from ''lingua'' "tongue") is a thin outgrowth at the junction of leaf and leafstalk of many grasses (Poaceae) and sedges. A ligule is also a strap-shaped extension of the corolla, such as that of a ...
or strap, and the reproductive parts. These include fused
anther
The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10
Morphology and terminology
A stamen typically consists of a stalk called the filam ...
s that form a tube which surrounds a
style
Style is a manner of doing or presenting things and may refer to:
* Architectural style, the features that make a building or structure historically identifiable
* Design, the process of creating something
* Fashion, a prevailing mode of clothing ...
and
bipartite stigma. As the anthers shed
pollen
Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophyt ...
, the style elongates to allow the stigmas, now coated with pollen, to emerge from the tube.
The ovaries form compressed,
obovate
The following is a list of terms which are used to describe leaf morphology in the description and taxonomy of plants. Leaves may be simple (a single leaf blade or lamina) or compound (with several leaflets). The edge of the leaf may be regular o ...
(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.
The domestication of lettuce over the centuries has resulted in several changes through
selective breeding
Selective breeding (also called artificial selection) is the process by which humans use animal breeding and plant breeding to selectively develop particular phenotypic traits (characteristics) by choosing which typically animal or plant mal ...
: delayed bolting, larger seeds, larger leaves and heads, better taste and texture, a lower
latex
Latex is an emulsion (stable dispersion) of polymer microparticles in water. Latexes are found in nature, but synthetic latexes are common as well.
In nature, latex is found as a milky fluid found in 10% of all flowering plants (angiosperms ...
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
Genetic engineering, also called genetic modification or genetic manipulation, is the modification and manipulation of an organism's genes using technology. It is a set of technologies used to change the genetic makeup of cells, including t ...
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
Herbicides (, ), also commonly known as weedkillers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page fo ...
tolerance, greater resistance to insects and fungi and slower bolting patterns. However, genetically modified lettuce is not currently used in commercial agriculture.
History
![Romaine lettuce](https://upload.wikimedia.org/wikipedia/commons/6/6b/Romaine_lettuce.jpg)
Lettuce was first cultivated in
ancient Egypt for the production of oil from its seeds. The plant was probably selectively bred by the Egyptians into a plant grown for its edible leaves,
[Katz and Weaver, pp. 375–376.] with evidence of its cultivation appearing as early as 2680 BC.
Lettuce was considered a sacred plant of the reproduction god
Min
Min or MIN may refer to:
Places
* Fujian, also called Mǐn, a province of China
** Min Kingdom (909–945), a state in Fujian
* Min County, a county of Dingxi, Gansu province, China
* Min River (Fujian)
* Min River (Sichuan)
* Mineola (Amtrak ...
, and was carried during his festivals and placed near his images. The plant was thought to help the god "perform the sexual act untiringly". 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 tall and resembled a large version of the modern
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, ...
. These upright lettuces were developed by the Egyptians and passed to the Greeks, who in turn shared them with the Romans. Around 50 AD, Roman agriculturalist
Columella
Lucius Junius Moderatus Columella (; Arabic: , 4 – ) was a prominent writer on agriculture in the Roman Empire.
His ' in twelve volumes has been completely preserved and forms an important source on Roman agriculture, together with the wo ...
described several lettuce varieties – some of which may have been ancestors of today's lettuces.
[Weaver, pp. 170–172.]
Lettuce appears in many medieval writings, especially as a medicinal herb.
Hildegard of Bingen
Hildegard of Bingen (german: Hildegard von Bingen; la, Hildegardis Bingensis; 17 September 1179), also known as Saint Hildegard and the Sibyl of the Rhine, was a German Benedictine abbess and polymath active as a writer, composer, philosopher ...
mentioned it in her writings on medicinal herbs between 1098 and 1179, and many early
herbal
A herbal is a book containing the names and descriptions of plants, usually with information on their medicinal, tonic, culinary, toxic, hallucinatory, aromatic, or magical powers, and the legends associated with them.Arber, p. 14. A herbal m ...
s also describe its uses. In 1586,
Joachim Camerarius
Joachim Camerarius (12 April 150017 April 1574), the Elder, was a Germans, German classical scholar.
Life
He was born in Bamberg, in the Prince-Bishopric of Bamberg. His family name was Liebhard, but he was generally called Kammermeister, previo ...
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
Christopher Columbus
* lij, Cristoffa C(or)ombo
* es, link=no, Cristóbal Colón
* pt, Cristóvão Colombo
* ca, Cristòfor (or )
* la, Christophorus Columbus. (; born between 25 August and 31 October 1451, died 20 May 1506) was a ...
in the late 15th century.
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.
[Weaver, pp. 172–173.]
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.
During the 1950s, lettuce production was revolutionized with the development of
vacuum cooling
Vacuum cooling is a rapid cooling technique for any porous product that has free water and uses the principle of evaporative cooling. Vacuum cooling is generally used for cooling food products that have a high water content and large porosities, ...
, which allowed field cooling and packing of lettuce, replacing the previously used method of ice-cooling in packing houses outside the fields.
Lettuce is very easy to grow, and as such has been a significant source of sales for many
seed companies
Seed companies produce and sell seeds for flowers, fruits and vegetables to commercial growers and amateur gardeners. The production of seed is a multibillion-dollar business, which uses growing facilities and growing locations worldwide. While ...
. 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. Although most lettuce grown today is used as a vegetable, a minor amount is used in the production of
tobacco-free cigarettes
Herbal cigarettes (also called tobacco-free cigarettes or nicotine-free cigarettes) are cigarettes that usually do not contain any tobacco or nicotine, instead being composed of a mixture of various herbs and/or other plant material. However, Chi ...
; however, domestic lettuce's wild relatives produce a leaf that visually more closely resembles tobacco.
Cultivation
![Park Lane Nurseries - geograph](https://upload.wikimedia.org/wikipedia/commons/c/cf/Park_Lane_Nurseries_-_geograph.org.uk_-_583201.jpg)
A
hardy annual, some varieties of lettuce can be
overwintered
Overwintering is the process by which some organisms pass through or wait out the winter season, or pass through that period of the year when "winter" conditions (cold or sub-zero temperatures, ice, snow, limited food supplies) make normal activi ...
even in relatively cold climates under a layer of straw, and older,
heirloom varieties
An heirloom plant, heirloom variety, heritage fruit (Australia and New Zealand), or heirloom vegetable (especially in Ireland and the UK) is an old cultivar
A cultivar is a type of cultivated plant that people have selected for desired trai ...
are often grown in
cold frame
In agriculture and gardening, a cold frame is a transparent-roofed enclosure, built low to the ground, used to protect plants from adverse weather, primarily excessive cold or wet. The transparent top admits sunlight and prevents heat escape via co ...
s.
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
transplant
Transplant or Transplantation may refer to:
Sciences
*Transplanting a plant from one location to another
*Organ transplantation, moving an organ from one body to another
*Transplant thought experiment, an experiment similar to Trolley problem
*Tra ...
ed to individual spots, usually 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.
![Planche Lactuca sativa](https://upload.wikimedia.org/wikipedia/commons/6/67/Planche_Lactuca_sativa.jpg)
Lettuce grows best in full sun in loose,
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
-rich soils with a
pH of between 6.0 and 6.8. Heat generally prompts lettuce to
bolt, with most varieties growing poorly above ; cool temperatures prompt better performance, with being preferred and as low as being tolerated.
Plants in hot areas that are provided partial shade during the hottest part of the day will bolt more slowly. Temperatures above will generally result in poor or non-existent germination of lettuce seeds.
After harvest, lettuce lasts the longest when kept at 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
A water footprint shows the extent of water use in relation to consumption by people. The water footprint of an individual, community, or business is defined as the total volume of fresh water used to produce the goods and services consumed by th ...
, with 237 liters of water required for each kilogram of lettuce produced. Hydroponic growing methods can reduce this water consumption by nearly two orders of magnitude.
Lettuce varieties will
cross
A cross is a geometrical figure consisting of two intersecting lines or bars, usually perpendicular to each other. The lines usually run vertically and horizontally. A cross of oblique lines, in the shape of the Latin letter X, is termed a sa ...
with each other, making spacing of between varieties necessary to prevent contamination when saving seeds. Lettuce will also cross with ''
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 tribe Cichorieae within the family Asterac ...
'' (wild lettuce), with the resulting seeds often producing a plant with tough, bitter leaves.
Celtuce
Celtuce () (''Lactuca sativa'' var. ''augustana'',Masatoshi Yamaguchi Caroline Foley ''angustata'', or ''asparagina''), also called stem lettuce, celery lettuce, asparagus lettuce, or Chinese lettuce, is a cultivar of lettuce grown primarily ...
, 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
The gene pool is the set of all genes, or genetic information, in any population, usually of a particular species.
Description
A large gene pool indicates extensive genetic diversity, which is associated with robust populations that can surv ...
. Starting in the 1990s, such programs began to include more distantly related species such as ''
L. tatarica''.
Seeds keep best when stored in cool conditions, and, unless stored
cryogenically
In physics, cryogenics is the production and behaviour of materials at very low temperatures.
The 13th IIR International Congress of Refrigeration (held in Washington DC in 1971) endorsed a universal definition of “cryogenics” and “cr ...
, remain viable the longest when stored at ; 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
Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...
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.
Cultivars (varieties)
![Lettuce mix](https://upload.wikimedia.org/wikipedia/commons/4/49/Lettuce_mix.jpg)
![Yangzhou - supermarket - woju - P1070028](https://upload.wikimedia.org/wikipedia/commons/6/64/Yangzhou_-_supermarket_-_woju_-_P1070028.JPG)
![Buttercrunch butterhead lettuce](https://upload.wikimedia.org/wikipedia/commons/9/99/Buttercrunch_butterhead_lettuce.jpg)
There are several types or
cultivar
A cultivar is a type of cultivated plant that people have selected for desired traits and when propagated retain those traits. Methods used to propagate cultivars include: division, root and stem cuttings, offsets, grafting, tissue culture, ...
s of lettuce. Three types – leaf, head and cos or romaine – are the most common.
[Bradley, p. 129.] There are seven main cultivar groups of lettuce, each including many varieties:
* 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.
*
Romaine/Cos—Used mainly for salads and sandwiches, this type forms long, upright heads.
This is the most often used lettuce in
Caesar salad
A Caesar salad (also spelled Cesar and Cesare) is a green salad of romaine lettuce and croutons dressed with lemon juice (or lime juice), olive oil, egg, Worcestershire sauce, anchovies, garlic, Dijon mustard, Parmesan cheese, and black pepper ...
s.
** Little Gem—a dwarf, compact romaine lettuce, popular in the UK.
* 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
Burpee Seeds and Plants, officially W. Atlee Burpee & Co., is an American Seed company, seed and plant company that was founded by Washington Atlee Burpee in Pennsylvania in 1876.
History
Early years (1876-1915)
W. Atlee Burpee & Company was ...
. It gets its name from the way it was transported in crushed ice, where the heads of lettuce looked like
iceberg
An iceberg is a piece of freshwater ice more than 15 m long that has broken off a glacier or an ice shelf and is floating freely in open (salt) water. Smaller chunks of floating glacially-derived ice are called "growlers" or "bergy bits". The ...
s. Today, it ships well, but is low in flavor and nutritional content, being composed of even more water than other lettuce types.
* Butterhead—Also known as Boston or Bibb lettuce,
and traditionally in the
UK as "round lettuce", this type is a head lettuce with a loose arrangement of leaves, known for its sweet flavor and tender texture.
* 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.
*
Celtuce
Celtuce () (''Lactuca sativa'' var. ''augustana'',Masatoshi Yamaguchi Caroline Foley ''angustata'', or ''asparagina''), also called stem lettuce, celery lettuce, asparagus lettuce, or Chinese lettuce, is a cultivar of lettuce grown primarily ...
/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.
* 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.
*
Red leaf lettuce
Red leaf lettuces are a group of lettuce cultivars
A cultivar is a type of Horticulture, cultivated plant that people have selected for desired phenotypic trait, traits and when Plant propagation, propagated retain those traits. Methods used ...
—A group of lettuce types with red leaves.
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.
Cultivation problems
![Starr 081031-0356 Lactuca sativa](https://upload.wikimedia.org/wikipedia/commons/5/5a/Starr_081031-0356_Lactuca_sativa.jpg)
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
cutworm
Cutworms are moth larvae that hide under litter or soil during the day, coming out in the dark to feed on plants. A larva typically attacks the first part of the plant it encounters, namely the stem, often of a seedling, and consequently cuts it ...
s, which cut seedlings off at the soil line;
wireworm
Elateridae or click beetles (or "typical click beetles" to distinguish them from the related families Cerophytidae and Eucnemidae, which are also capable of clicking) are a family of beetles. Other names include elaters, snapping beetles, spr ...
s and
nematode
The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-Parasitism, parasitic nematodes also known as eelworms. They are a diverse animal phylum inhab ...
s, which cause yellow, stunted plants;
tarnished plant bug
The tarnished plant bug (TPB), ''Lygus lineolaris'', is a species of plant-feeding insect in the family Miridae. It has piercing-sucking mouthparts and has become a serious pest on small fruits and vegetables in North America. It is considered a ...
s and
aphid
Aphids are small sap-sucking insects and members of the superfamily Aphidoidea. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white woolly aphids. A t ...
s, which cause yellow, distorted leaves;
leafhopper
A leafhopper is the common name for any species from the family Cicadellidae. These minute insects, colloquially known as hoppers, are plant feeders that suck plant sap from grass, shrubs, or trees. Their hind legs are modified for jumping, and a ...
s, which cause stunted growth and pale leaves;
thrip
Thrips ( order Thysanoptera) are minute (mostly long or less), slender insects with fringed wings and unique asymmetrical mouthparts. Different thrips species feed mostly on plants by puncturing and sucking up the contents, although a few are ...
s, which turn leaves gray-green or silver;
leafminer
A leaf miner is any one of numerous species of insects in which the larval stage lives in, and eats, the leaf tissue of plants. The vast majority of leaf-mining insects are moths (Lepidoptera), sawflies (Symphyta, the mother clade of wasps), ...
s, which create tunnels within the leaves;
flea beetle
The flea beetle is a small, jumping beetle of the leaf beetle family (Chrysomelidae), that makes up the tribe Alticini which is part of the subfamily Galerucinae. Historically the flea beetles were classified as their own subfamily.
Though m ...
s, which cut small holes in leaves and
caterpillar
Caterpillars ( ) are the larval stage of members of the order Lepidoptera (the insect order comprising butterflies and moths).
As with most common names, the application of the word is arbitrary, since the larvae of sawflies (suborder Sym ...
s,
slug
Slug, or land slug, is a common name for any apparently shell-less terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced shell, or only a smal ...
s and
snail
A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class Gastro ...
s, which cut large holes in leaves. For example, the larvae of the
ghost moth
The ghost moth or ghost swift (''Hepialus humuli'') is a moth of the family Hepialidae. It is common throughout Europe, except for in the far south-east.
Female ghost moths are larger than males, and exhibit sexual dimorphism with their differ ...
is a common pest of lettuce plants.
Mammals, including
rabbit
Rabbits, also known as bunnies or bunny rabbits, are small mammals in the family Leporidae (which also contains the hares) of the order Lagomorpha (which also contains the pikas). ''Oryctolagus cuniculus'' includes the European rabbit speci ...
s and
groundhog
The groundhog (''Marmota monax''), also known as a woodchuck, is a rodent of the family Sciuridae, belonging to the group of large ground squirrels known as marmots.
The groundhog is a lowland creature of North America; it is found through mu ...
s, also eat the plants.
[Bradley, pp. 129–132.] Lettuce contains several defensive compounds, including
sesquiterpene lactone
Sesquiterpene lactones (SLs) are a class of sesquiterpenoids that contain a lactone ring. They are most often found in plants of the family Asteraceae (daisies, asters). Other plant families with SLs are Umbelliferae (celery, parsley, carrots) an ...
s, and other natural
phenolics such as
flavonol
Flavonols are a class of flavonoids that have the 3-hydroxyflavone backbone (IUPAC name : 3-hydroxy-2-phenylchromen-4-one). Their diversity stems from the different positions of the phenolic -OH groups. They are distinct from flavanols (with "a ...
and
glycosides
In chemistry, a glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive 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.
Lettuce also suffers from several
viral diseases
Viral means "relating to viruses" (small infectious agents).
Viral may also refer to:
Viral behavior, or virality
Memetic behavior likened that of a virus, for example:
* Viral marketing, the use of existing social networks to spread a marke ...
, including
big vein, which causes yellow, distorted leaves, and
mosaic virus
A mosaic virus is any virus that causes infected plant foliage to have a mottled appearance. Such viruses come from a variety of unrelated lineages and consequently there is no taxon that unites all mosaic viruses. All the symptoms of each virus ...
, which is spread by aphids and causes stunted plant growth and deformed leaves.
Aster yellows
Aster yellows is a chronic, systemic plant disease caused by several bacteria called phytoplasma. The aster yellows phytoplasma (AYP) affects 300 species in 38 families of broad-leaf herbaceous plants, primarily in the aster family, as well as im ...
are a disease-causing bacteria carried by leafhoppers, which causes deformed leaves. Fungal diseases include
powdery mildew
Powdery mildew is a fungal disease that affects a wide range of plants. Powdery mildew diseases are caused by many different species of ascomycete fungi in the order Erysiphales. Powdery mildew is one of the easier plant diseases to identify, as ...
and
downy mildew
Downy mildew refers to any of several types of oomycete microbes that are obligate parasites of plants. Downy mildews exclusively belong to the Peronosporaceae family. In commercial agriculture, they are a particular problem for growers of crucif ...
, which cause leaves to mold and die and
bottom rot,
lettuce drop and
gray mold
''Botrytis cinerea'' is a necrotrophic fungus that affects many plant species, although its most notable hosts may be wine grapes. In viticulture, it is commonly known as "botrytis bunch rot"; in horticulture, it is usually called "grey mould" or ...
, which cause entire plants to rot and collapse.
Bacterial diseases include ''
Botrytis cinerea
''Botrytis cinerea'' is a necrotrophic fungus that affects many plant species, although its most notable hosts may be wine grapes. In viticulture, it is commonly known as "botrytis bunch rot"; in horticulture, it is usually called "grey mould" or ...
'', for which
UV-C
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...
treatments may be used: Vàsquez et al. 2017 find that
phenylalanine ammonia-lyase
The enzyme phenylalanine ammonia lyase (EC 4.3.1.24) catalyzes the conversion of L-phenylalanine to ammonia and ''trans''-cinnamic acid.:
:L-phenylalanine = ''trans''-cinnamate + NH3
Phenylalanine ammonia lyase (PAL) is the first and committed ...
activity, phenolic production, and ''B. cinerea''
resistance
Resistance may refer to:
Arts, entertainment, and media Comics
* Either of two similarly named but otherwise unrelated comic book series, both published by Wildstorm:
** ''Resistance'' (comics), based on the video game of the same title
** ''T ...
are increased by UV-C.
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. Herbicides are often used to control weeds in commercial production. However, this has led to the development of
herbicide-resistant
Pesticide resistance describes the decreased susceptibility of a pest population to a pesticide that was previously effective at controlling the pest. Pest species evolve pesticide resistance via natural selection: the most resistant specimens su ...
weeds in lettuce cultivation.
Production
In 2020, world production of lettuce (report combined with
chicory
Common chicory ('' Cichorium intybus'') is a somewhat woody, perennial herbaceous plant of the family Asteraceae, usually with bright blue flowers, rarely white or pink. Native to the Old World, it has been introduced to North America and Austra ...
) was 28 million tonnes, with
China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
alone producing 14.3 million tonnes or 52% of the world total (see table).
Lettuce is the only member of the genus ''Lactuca'' to be grown commercially. 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.
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.
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.
In the United States in 2013, California
California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...
(71%) and Arizona
Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...
(29%) produced nearly all of the country's fresh head and leaf lettuce, with head lettuce yielding $9,400 of value per acre and leaf lettuce yielding $8,000 per acre.
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
Domitian (; la, Domitianus; 24 October 51 – 18 September 96) was a Roman emperor who reigned from 81 to 96. The son of Vespasian and the younger brother of Titus, his two predecessors on the throne, he was the last member of the Flavi ...
, the tradition of serving a lettuce salad
A salad is a dish consisting of mixed, mostly natural ingredients with at least one raw ingredient. They are typically served at room temperature or chilled, though some can be served warm. Condiments and salad dressings, which exist in a va ...
before a meal began. Post-Roman Europe continued the tradition of poaching
Poaching has been defined as the illegal hunting or capturing of wild animals, usually associated with land use rights.
Poaching was once performed by impoverished peasants for subsistence purposes and to supplement meager diets. It was set a ...
lettuce, mainly with large romaine types, as well as the method of pouring a hot oil and vinegar mixture over the leaves.
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 salad
A Caesar salad (also spelled Cesar and Cesare) is a green salad of romaine lettuce and croutons dressed with lemon juice (or lime juice), olive oil, egg, Worcestershire sauce, anchovies, garlic, Dijon mustard, Parmesan cheese, and black pepper ...
s. Lettuce leaves can also be found in soups, sandwiches and wraps, while the stems are eaten both raw and cooked.
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
A bean is the seed of several plants in the family Fabaceae, which are used as vegetables for human or animal food. They can be cooked in many different ways, including boiling, frying, and baking, and are used in many traditional dishes thr ...
and meat dishes, soups and stir-fry
Stir frying () is a cooking technique in which ingredients are fried in a small amount of very hot oil while being stirred or tossed in a wok. The technique originated in China and in recent centuries has spread into other parts of Asia and th ...
s 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
Lettuce soup is a soup prepared with lettuce as a primary ingredient. It may be prepared with myriad lettuces and other ingredients, and some lettuce soups may use several cultivars of lettuce in their preparation. It is a part of French cuisine ...
.
Nutritional content
Depending on the variety, lettuce is an excellent source (20% of the Daily Value
The Reference Daily Intake (RDI) used in nutrition labeling on food and dietary supplement products in the U.S. and Canada is the daily intake level of a nutrient that is considered to be sufficient to meet the requirements of 97–98% of health ...
, DV, or higher) of vitamin K
Vitamin K refers to structurally similar, fat-soluble vitamers found in foods and marketed as dietary supplements. The human body requires vitamin K for post-synthesis modification of certain proteins that are required for blood coagulation ...
(97% DV) and vitamin A
Vitamin A is a fat-soluble vitamin and an essential nutrient for humans. It is a group of organic compounds that includes retinol, retinal (also known as retinaldehyde), retinoic acid, and several provitamin A carotenoids (most notably bet ...
(21% DV) (table), with higher concentrations of the provitamin A A provitamin is a substance that may be converted within the body to a vitamin. The term previtamin is a synonym.
The term "provitamin" is used when it is desirable to label a substance with little or no vitamin activity, but which can be converted ...
compound, beta-carotene, found in darker green lettuces, such as romaine. With the exception of the iceberg variety, lettuce is also a good source (10–19% DV) of folate
Folate, also known as vitamin B9 and folacin, is one of the B vitamins. Manufactured folic acid, which is converted into folate by the body, is used as a dietary supplement and in food fortification as it is more stable during processing and ...
and iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
(table).
Food-borne illness
Food-borne pathogen
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...
s that can survive on lettuce include ''Listeria monocytogenes
''Listeria monocytogenes'' is the species of pathogenic bacteria that causes the infection listeriosis. It is a facultative anaerobic bacterium, capable of surviving in the presence or absence of oxygen. It can grow and reproduce inside the host' ...
'', the causative agent of listeriosis
Listeriosis is a bacterial infection most commonly caused by ''Listeria monocytogenes'', although '' L. ivanovii'' and '' L. grayi'' have been reported in certain cases. Listeriosis can cause severe illness, including severe sepsis, men ...
, 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
Shelf life is the length of time that a commodity may be stored without becoming unfit for use, consumption, or sale. In other words, it might refer to whether a commodity should no longer be on a pantry shelf (unfit for use), or no longer on a ...
, indigenous microflora competing with the ''Listeria'' bacteria or inhibition of bacteria to cause listeriosis.
Other bacteria found on lettuce include ''Aeromonas
''Aeromonas'' is a genus of Gram-negative, facultative anaerobic, rod-shaped bacteria that morphologically resemble members of the family Enterobacteriaceae. Most of the 14 described species have been associated with human diseases. The most imp ...
'' species, which have not been linked to any outbreaks; ''Campylobacter
''Campylobacter'' (meaning "curved bacteria") is a genus of Gram-negative bacteria. ''Campylobacter'' typically appear comma- or s-shaped, and are motile. Some ''Campylobacter'' species can infect humans, sometimes causing campylobacteriosis, a d ...
'' species, which cause campylobacteriosis
Campylobacteriosis is an infection by the '' Campylobacter'' bacterium, most commonly ''C. jejuni''. It is among the most common bacterial infections of humans, often a foodborne illness. It produces an inflammatory, sometimes bloody, diarrhea or ...
; and ''Yersinia intermedia
''Yersinia intermedia'' is a Gram-negative species of bacteria which uses rhamnose, melibiose, and raffinose. Its type strain is strain 3953 (=CIP 80-28 =ATCC 29909 =Bottone 48 =Chester 48). It has been found in fish, and contains several biotype ...
'' and ''Yersinia kristensenii
''Yersinia kristensenii'' is a species of bacteria.Bercovier, Hervé, et al. "Yersinia kristensenii: A new species of Enterobacteriaceae composed of sucrose-negative strains (formerly called atypical Yersinia enterocolitica or Yersinia enterocoli ...
'' (species of ''Yersinia
''Yersinia'' is a genus of bacteria in the family Yersiniaceae. ''Yersinia'' species are Gram-negative, coccobacilli bacteria, a few micrometers long and fractions of a micrometer in diameter, and are facultative anaerobes. Some members of ''Ye ...
''), which have been found mainly in lettuce. Lettuce has been linked to numerous outbreaks of the bacteria '' E. coli O157:H7'' and ''Shigella
''Shigella'' is a genus of bacteria that is Gram-negative, facultative anaerobic, non-spore-forming, nonmotile, rod-shaped, and genetically closely related to ''E. coli''. The genus is named after Kiyoshi Shiga, who first discovered it in 1897. ...
''; the plants were most likely contaminated through contact with animal feces. 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''. ''Salmonella
''Salmonella'' is a genus of rod-shaped (bacillus) Gram-negative bacteria of the family Enterobacteriaceae. The two species of ''Salmonella'' are ''Salmonella enterica'' and ''Salmonella bongori''. ''S. enterica'' is the type species and is fur ...
'' bacteria, including the uncommon ''Salmonella braenderup
''Salmonella'' is a genus of rod-shaped (bacillus) Gram-negative bacteria of the family Enterobacteriaceae. The two species of ''Salmonella'' are ''Salmonella enterica'' and ''Salmonella bongori''. ''S. enterica'' is the type species and is furt ...
'' type, have also caused outbreaks traced to contaminated lettuce. Viruses, including hepatitis A
Hepatitis A is an infectious disease of the liver caused by ''Hepatovirus A'' (HAV); it is a type of viral hepatitis. Many cases have few or no symptoms, especially in the young. The time between infection and symptoms, in those who develop them ...
, calicivirus
The ''Caliciviridae'' are a family of "small round structured" viruses, members of Class IV of the Baltimore scheme. Caliciviridae bear resemblance to enlarged picornavirus and was formerly a separate genus within the picornaviridae. They are p ...
and a Norwalk-like strain, have been found in lettuce. The vegetable has also been linked to outbreaks of parasitic infestations, including ''Giardia lamblia
''Giardia duodenalis'', also known as ''Giardia intestinalis'' and ''Giardia lamblia'', is a flagellated parasitic microorganism of the genus '' Giardia'' that colonizes the small intestine, causing a diarrheal condition known as giardiasis. Th ...
''.
Religious symbolism and medicinal use
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) folk medicine
Traditional medicine (also known as indigenous medicine or folk medicine) comprises medical aspects of traditional knowledge that developed over generations within the folk beliefs of various societies, including indigenous peoples, before the ...
and religious symbolism
A religious symbol is an iconic representation intended to represent a specific religion, or a specific concept within a given religion.
Religious symbols have been used in the military in many countries, such as the United States military chapl ...
. For example, ancient Egyptians thought lettuce to be a symbol of sexual prowess and a promoter of love and childbearing in women. The Romans likewise claimed that it increased sexual potency. In contrast, the ancient Greeks connected the plant with male impotency, and served it during funerals (probably due to its role in the myth of Adonis
In Greek mythology, Adonis, ; derived from the Canaanite word ''ʼadōn'', meaning "lord". R. S. P. Beekes, ''Etymological Dictionary of Greek'', Brill, 2009, p. 23. was the mortal lover of the goddess Aphrodite.
One day, Adonis was gored by ...
' death), and British women in the 19th century believed it would cause infertility and sterility.
Lettuce has mild narcotic
The term narcotic (, from ancient Greek ναρκῶ ''narkō'', "to make numb") originally referred medically to any psychoactive compound with numbing or paralyzing properties. In the United States, it has since become associated with opiates ...
properties; it was called "sleepwort" by the Anglo-Saxons
The Anglo-Saxons were a Cultural identity, cultural group who inhabited England in the Early Middle Ages. They traced their origins to settlers who came to Britain from mainland Europe in the 5th century. However, the ethnogenesis of the Anglo- ...
because of this attribute, although the cultivated ''L. sativa'' has lower levels of the narcotic than its wild cousins. This narcotic effect is a property of two sesquiterpene lactone
Sesquiterpene lactones (SLs) are a class of sesquiterpenoids that contain a lactone ring. They are most often found in plants of the family Asteraceae (daisies, asters). Other plant families with SLs are Umbelliferae (celery, parsley, carrots) an ...
s (lactucin
Lactucin is a bitter substance that forms a white crystalline solid and belongs to the group of sesquiterpene lactones. It is found in some varieties of lettuce and is an ingredient of lactucarium. It has been shown to have analgesic and sedativ ...
and lactucopicrin
Lactucopicrin (Intybin) is a bitter substance that has a sedative and analgesic effect, acting on the central nervous system. It is a sesquiterpene lactone, and is a component of lactucarium, derived from the plant ''Lactuca virosa'' (wild lettuce ...
) which are found in the white liquid (latex) in the stems of lettuce,[Katz and Weaver, p. 377.] called lactucarium
Lactucarium is the milky fluid secreted by several species of lettuce, especially ''Lactuca virosa'', usually from the base of the stems. It is known as lettuce opium because of its sedative and analgesic properties. It has also been reported ...
or "lettuce opium". Although the standard definition of lactucarium requires its production from ''Lactuca virosa
''Lactuca virosa'' is a plant in the ''Lactuca'' (lettuce) genus, often ingested 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, opi ...
'' or "wild lettuce
Wild lettuce is a common name for several lactucarium-containing plants related to lettuce (''Lactuca sativa''). The name most often refers to ''Lactuca virosa'' (Europe, Asia, introduced to North America), though it may also refer to:
* ''Lactuc ...
", it was recognized that smaller quantities of lactucarium could be produced in a similar way from ''Lactuca sativa
Lettuce (''Lactuca sativa'') is an annual plant of the 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, ...
'' and ''Lactuca canadensis
''Lactuca canadensis'' is a species of wild lettuce known by the common names Canada lettuce, Canada wild lettuce, tall lettuce, and Florida blue lettuce.Weakley, Alan S''. Flora of the Southern and Mid-Atlantic States.'' UNC Herbarium, North Car ...
'' var. ''elongata'', and that lettuce-opium obtained from ''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 tribe Cichorieae within the family Asterac ...
'' or ''Lactuca quercina
''Lactuca quercina'' is a species of wild lettuce native to Europe and Asia. It is an annual or biennial herb in the tribe Cichorieae within the family Asteraceae growing from a taproot to maximum heights of or more.
''Lactuca quercina'' contai ...
'' was of superior quality.
Romaine lettuce is one of the symbolic items on the Jewish
Jews ( he, יְהוּדִים, , ) or Jewish people are an ethnoreligious group and nation originating from the Israelites Israelite origins and kingdom: "The first act in the long drama of Jewish history is the age of the Israelites""The ...
Passover Seder
The Passover Seder (; he, סדר פסח , 'Passover order/arrangement'; yi, סדר ) is a ritual feast at the beginning of the Jewish holiday of Passover. It is conducted throughout the world on the eve of the 15th day of Nisan in the Hebrew c ...
plate as a bitter herb (maror
''Maror'' ( he, מָרוֹר ''mārôr'') refers to the bitter herbs eaten at the Passover Seder in keeping with the biblical commandment "with bitter herbs they shall eat it." (Exodus 12:8).
Biblical source
In some listings of the 613 comman ...
).
Some American settlers claimed that smallpox
Smallpox was an infectious disease caused by variola virus (often called smallpox virus) which belongs to the genus Orthopoxvirus. The last naturally occurring case was diagnosed in October 1977, and the World Health Organization (WHO) c ...
could be prevented through the ingestion of lettuce, and an Iranian belief suggested consumption of the seeds when afflicted with typhoid
Typhoid fever, also known as typhoid, is a disease caused by '' Salmonella'' serotype Typhi bacteria. Symptoms vary from mild to severe, and usually begin six to 30 days after exposure. Often there is a gradual onset of a high fever over several ...
. Scientific evidence of these benefits in humans has not been found. The religious ties of lettuce continue into the present day among the Yazidi
Yazidis or Yezidis (; ku, ئێزیدی, translit=Êzidî) are a Kurmanji-speaking endogamous minority group who are indigenous to Kurdistan, a geographical region in Western Asia that includes parts of Iraq, Syria, Turkey and Iran. The majo ...
people of northern Iraq, who have a religious prohibition against eating the plant.
References
Cited literature
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{{Authority control
Leaf vegetables
Crops
Crops originating from Egypt
sativa
Sativa, sativus, and sativum are Latin botanical adjectives meaning '' cultivated''. It is often associated botanically with plants that promote good health and used to designate certain seed-grown domestic crops.
Usage
''Sativa'' (ending in -a) ...