Lettuce
Lettuce | |
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A field of iceberg lettuces in California | |
Scientific classification | |
Kingdom: | Plantae |
Clade: | Tracheophytes |
Clade: | Angiosperms |
Clade: | Eudicots |
Clade: | Asterids |
Order: | Asterales |
Family: | Asteraceae |
Genus: | Lactuca |
Species: | L. sativa
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Binomial name | |
Lactuca sativa | |
Synonyms[1][2] | |
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Lettuce (Lactuca sativa) is an
Lettuce was originally farmed by the
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.
Taxonomy and etymology
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 "dairy" in Latin), an allusion to the white substance, latex, exuded by cut stems.[10] The name Lactuca 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 the variety of lettuce grown 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 Kos, a center of lettuce farming in the Byzantine period.[13]
Description
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.
The domestication of lettuce over the centuries has resulted in several changes through
History
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,[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 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. Around 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.[citation needed] 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.[27]
Lettuce is easy to grow, and as such has been a significant source of sales for many
Cultivation
A
Lettuce grows best in full sun in loose,
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)
There are several types or cultivars of lettuce. Three types – leaf, head and cos or romaine – are the most common.[30] 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.[31]
- Romaine/Cos—Used mainly for salads and sandwiches, this type forms long, upright heads.[31] This is the most often used lettuce in Caesar salads.[24]
- Little Gem—a dwarf, compact romaine lettuce, popular in the UK.[36]
- Iceberg/Crisphead—The most popular type in the United States. Iceberg lettuce is very heat-sensitive and was originally developed in 1894 for growth in the northern United States by Burpee Seeds and Plants. It gets its name from the way it was transported in crushed ice, where the heads of lettuce looked like icebergs.[37] Today, it ships well, but is low in flavor and nutritional content, being composed of even more water than other lettuce types.[31]
- Butterhead—Also known as Boston or Bibb lettuce,
- 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.[31]
- 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.[39]
- Red leaf lettuce—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.[40]
Cultivation problems
Soil nutrient deficiencies can cause a variety of plant problems that range from malformed plants to a lack of head growth.
Lettuce also suffers from several
Production
Country | Millions of tonnes |
---|---|
China | 15.0 |
United States | 3.3 |
India | 1.2 |
Spain | 1.0 |
Italy | 0.7 |
Mexico | 0.6 |
World | 27.1 |
Source: FAO[4]
|
In 2022, world production of lettuce (report combined with chicory) was 27 million tonnes, with China alone producing 55% of the world total (table).
Lettuce is the only member of the genus Lactuca to be grown commercially.[46] Although China is the top world producer of lettuce, the majority of the crop is consumed domestically.
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.[47] Stem lettuce was first developed in China, where it remains primarily cultivated.[48]
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.[49][50][51]
In the United States in 2022, lettuce was the main vegetable ingredient in salads, and was the most consumed among leaf vegetables; its market was about 20% of all vegetables, with Romaine and iceberg having about equal sales.[50] Some 85% of the lettuce consumed in the United States in 2022 was produced domestically.[50]
Uses
Culinary
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. Lettuce leaves can also be found in soups, sandwiches and wraps, while the stems are eaten both raw and cooked.[11]
Nutritional value per 100 g (3.5 oz) | |
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Energy | 58 kJ (14 kcal) |
3.0 g | |
Sugars | 2.0 g |
Dietary fiber | 1.2 g |
0.14 g | |
0.9 g | |
beta-Carotene | 3% 25 μg3% 299 μg277 μg |
Thiamine (B1) | 3% 0.041 mg |
Riboflavin (B2) | 2% 0.025 mg |
Pantothenic acid (B5) | 2% 0.091 mg |
Vitamin B6 | 2% 0.042 mg |
Folate (B9) | 7% 29 μg |
Vitamin C | 3% 2.8 mg |
Vitamin E | 1% 0.18 mg |
Vitamin K | 20% 24.1 μg |
Minerals | Quantity %DV† |
Calcium | 1% 18 mg |
Iron | 2% 0.41 mg |
Magnesium | 2% 7 mg |
Manganese | 5% 0.125 mg |
Phosphorus | 2% 20 mg |
Potassium | 5% 141 mg |
Sodium | 0% 10 mg |
Zinc | 1% 0.15 mg |
Other constituents | Quantity |
Water | 95.6 g |
†Percentages estimated using US recommendations for adults,[52] except for potassium, which is estimated based on expert recommendation from the National Academies.[53] |
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
Nutrition
Raw iceberg lettuce is 96% water, 3%
In lettuce varieties with dark green leaves, such as
Food-borne illness
Other bacteria found on lettuce include
Lettuce has been linked to numerous outbreaks of the bacteria
Due to the increase in food demand, the use of treated wastewater effluent for irrigation and animal or human excreta (i.e., manure or biosolids) as soil amendments is increasing.
Pathogens found on lettuce are not specific to lettuce (though some E. coli strains have affinity for Romaine). But, unlike other vegetables which tend to be cooked, lettuce is eaten raw, thus food-borne outbreaks associated with it are more frequent and affect a larger number of people.[64]
References
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- ^ a b "Lactuca serriola L". United States Department of Agriculture. Archived from the original on 5 June 2012. Retrieved 2 April 2012.
- ^ Hugh Fearnley-Whittingstall. "Grilled lettuce with goats' cheese". BBC. Archived from the original on 17 July 2013. Retrieved 17 May 2013.
- ^ a b "Lettuce (with chicory) production in 2022; Countries/Regions/Production Quantity/Year from pick lists". UN Food & Agriculture Organization, Statistics Division (FAOSTAT). 2024. Retrieved 16 April 2024.
- ^ "Lactuca sativa L". Integrated Taxonomic Information System. Archived from the original on 25 October 2011. Retrieved 27 March 2010.
- doi:10.5519/qwv6u7j5. Archivedfrom the original on 22 December 2015. Retrieved 17 December 2015.
- ^ "Lactuca sativa L". United States Department of Agriculture. Archived from the original on 8 June 2012. Retrieved 2 April 2012.
- ^ Porcher, Michael H. (2005). "Sorting Lactuca Names". Multilingual Multiscript Plant Name Database. University of Melbourne. Archived from the original on 16 September 2012. Retrieved 2 April 2012.
- ISBN 978-0-19-954906-1. Archivedfrom the original on 23 July 2016. Retrieved 10 January 2016.
- ^ a b c d Weaver, pp. 170–172.
- ^ a b Katz and Weaver, p. 376.
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- ^ a b Weaver, p. 172.
- ^ "Lactuca sativa". Missouri Botanical Garden. Archived from the original on 16 June 2013. Retrieved 27 March 2012.
- ^ ISBN 978-1-60085-303-6. Archivedfrom the original on 20 May 2021. Retrieved 6 October 2020.
- ^ a b c Ryder, J.; Waycott, Williams (1993). "New Directions in Salad Crops: New Forms, New Tools, and Old Philosophy". In Janick, J.; Simon, J.E. (eds.). New Crops. Wiley. pp. 528–532. Archived from the original on 17 July 2012. Retrieved 11 April 2012.
- ^ Smith, Richard; Cahn, Michael; Daugovish, Oleg; Koike, Steven; Natwick, Eric; Smith, Hugh; Subbarao, Krishna; Takele, Etaferahu; Turin, Thomas. "Leaf Lettuce Production in California" (PDF). University of California Vegetable Research and Information Center. Archived from the original (PDF) on 19 June 2012. Retrieved 11 April 2012.
- ^ a b c d Weaver, pp. 175–176.
- ^ Barkley, Theodore M.; Brouillet, Luc; Strother, John L. "Asteraceae tribe Cichorieae". In Flora of North America Editorial Committee (ed.). Flora of North America North of Mexico (FNA). Vol. 19, 20 and 21. New York and Oxford: Oxford University Press. Retrieved 24 September 2012 – via eFloras.org, Missouri Botanical Garden, St. Louis, MO & Harvard University Herbaria, Cambridge, MA.
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- ^ a b "Vegetable of the Month: Lettuce". Centers for Disease Control and Prevention. Archived from the original on 22 March 2012. Retrieved 26 March 2012.
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- ^ a b Weaver, pp. 172–173.
- ^ Enochian, R.V.; Smith, F.J (November 1956). "House Packing Western Lettuce" (PDF). California Agriculture. Archived from the original (PDF) on 15 June 2013.
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- ^ "Lactuca sativa 'Little Gem' | lettuce (Cos) 'Little Gem' Annual Biennial/RHS Gardening". www.rhs.org.uk. Retrieved 14 November 2022.
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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. Vol. 59. Springer. ISBN 978-3-540-36752-9.
- Katz, Solomon H.; Weaver, Williams Woys (2003). Encyclopedia of Food and Culture. Vol. 2. Scribner. ISBN 978-0-684-80565-8.
- Weaver, William 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