lettuce

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iceberg lettuce

A plant originally from the eastern Mediterranean region and western Asia. There are many varieties of lettuce.

Crisphead lettuce has outer leaves that are green and crunchy, with leaves that are more yellow or white at the center. The most well-known crisphead lettuce is iceberg lettuce.
Butterhead lettuce has very tender leaves. The most well-known butterhead lettuces in North America are Bibb lettuce and Boston lettuce.
Green leaf lettuce is a non-head lettuce with curly, wavy leaves. It covers several varieties, all with long, large leaves that are tender and tasty. Some have a slightly nutty taste.
Romaine or cos lettuce has long, firm, very crisp leaves with an even green color. The leaves have a central rib that is rigid, fibrous and especially crunchy.
Celtuce (also called "asparagus" or "stem lettuce") is a cross between celery and lettuce. Its flavor is reminiscent of both of these vegetables.

Buying

Choose: lettuce with a tight head and shiny, firm, crunchy leaves.

Avoid: limp, dull, waterlogged lettuce with discolored or yellowed parts, or whose ends are dried out or browned.

Preparing

Remove the lettuce core to separate the leaves more easily. Remove any wilted outer leaves and hard parts. Wash lettuce carefully to remove dirt and insects. Some varieties, including green leaf lettuce, require meticulous cleaning. Wash the leaves, changing the water if necessary, by shaking them gently and without letting them soak. Drain carefully. Tear lettuce into pieces by hand rather than using a knife, as this will discolor the edges. Do not remove lettuce from the fridge or add dressing until serving to avoid it going limp. If the lettuce is too bitter, it can be blanched by being plunged in boiling water for a few minutes.

Serving Ideas

Lettuce is most often eaten raw, but it can also be cooked. Raw lettuce is mainly served as a salad, dressed with vinaigrette or mayonnaise, or used in sandwiches. Combining several varieties of lettuce in a salad improves its look, flavor and nutritional value. Romaine lettuce is used in the classic Caesar salad.

Lettuce is often braised or used in soups. Finely shredded lettuce leaves added to a soup at the end of the cooking time add a delicate flavor to the broth. Puréed lettuce leaves also make an excellent soup.

Storing

In the fridge: wash green leaf lettuce and romaine lettuce before refrigerating. Other lettuces should only be washed just before using. Wrap lettuce loosely in a damp cloth or in an airtight container (3-5 days for romaine lettuce, 1-2 weeks for iceberg lettuce and 2-3 days for Boston and green leaf lettuce).

Keep lettuce away from fruits or vegetables that emit a lot of ethylene (apples, pears, bananas, cantaloupes and tomatoes), as this gas browns the leaves. Lettuce can be crisped by plunging in cold water.

Nutritional Information

Boston lettuce

green leaf lettuce

romaine or cos lettuce

celtuce

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Lettuce (Lactuca sativa, variety capitata) (credit: Derek Fell)

Cultivated annual salad plant (Lactuca sativa) that produces clusters of crisp, water-filled leaves. The best-known varieties are head, or cabbage, lettuce (variety capitata); leaf, or curled, lettuce (variety crispa); cos, or romaine, lettuce (variety longifolia); and asparagus lettuce (variety asparagina). Head lettuce is further divided into butter heads and crisp heads (e.g., iceberg lettuce). In the U.S, large-scale farms grow mainly crisp-head varieties, shipping them nationwide. Small-scale, local farmers raise leaf and butter-head varieties. Lettuce is an early annual crop that grows best in cool weather and with ample water. Though usually consumed in salads, it may also be cooked.

For more information on lettuce, visit Britannica.com.

A cool-season annual, Lactuca sativa, of Asian origin and belonging to the tribe Cichorium of the Compositae family. Lettuce is grown for its succulent leaves, which are eaten raw as a salad. Four varieties of this leading salad crop are head lettuce (L. sativa var. capitata), leaf or curied lettuce (L. sativa var. crispa) cos or romaine lettuce (L. sativa var. longifolia), and stem or asparagus lettuce (L. sativa var. asparagina). There are two types of head lettuce: butterhead, and crisphead or iceberg.

California raises more lettuce than any other state; Arizona, Florida, and Texas are next in importance. See also Asterales.

Leaves of the plant Lactuca sativa; many varieties are grown commercially. A poor source of nutrients; an 80-g portion supplies 10 kcal (40 kJ).

There are hundreds of lettuce varieties grown throughout the world and, because they peak at different times of year, there's always a plenitude of this universal salad favorite. There are four general lettuce classifications-butterhead, crisphead, leaf and romaine (see individual listings), most of which comprise many varieties. When shopping for any kind of lettuce a general rule of thumb is to choose those that are crisp and free of blemishes. As with all greens, lettuce should be washed and either drained completely or blotted with a paper towel to remove any excess moisture. A salad spinner, which uses centrifugal force to remove water from leafy greens, is a real time-saver for this process. Never allow lettuce to soak, as the water tends to soften some leaves. Refrigerate washed-and-dried greens airtight in a plastic bag for 3 to 5 days, depending on the variety. All lettuce is low calorie and most of it is rich in calcium, iron and vitamins A and C. Keep in mind that the darker green leaves contain the most nutrients.

noun

Something, such as coins or printed bills, used as a medium of exchange: cash, currency, lucre, money. Informal wampum. Slang bread, cabbage, dough, gelt, green, jack, long green, mazuma, moola, scratch. Chiefly British brass. See money.

English lore seems a little confused about the lettuce. On the one hand we are assured that lettuce brings about sterility in men (Dodoens, Herball (1578), and Folkard, Plant Lore (1884), both quoted in Opie and Tatem), or that ‘o' ermuch lettuce in the garden will stop a young wife's bearing’ (N&Q 1s:7 (1853), 152). On the other hand, the Radfords and Hole assure us that lettuces ‘were also said to promote child-bearing if eaten in salads by young women, or taken in the form of decoctions made from the juice or seeds’. They quote a letter from a woman published in the Daily Mirror (26 July 1951) saying she was advised by a specialist to eat lettuce to help remedy her childlessness, and that the remedy worked.

Bibliography
The full bibliography list is available here.

• Opie and Tatem, 1989: 232
• Radford, Radford, and Hole, 1961: 217

Lettuce has been described as a "weedy Cinderella" by T. W. Whitaker (1974) and as the "queen of the salad plants" by Franklin W. Martin and Ruth M. Ruberté (1975). What is this plant that merits two such disparate descriptions? It is certainly the most commonly used salad vegetable, occurring in or under most salads. Many types exist, varying in size, form, leaf shape, color, and taste. All of these types may have evolved from a weedy form that was used in ancient Egypt as a source of cooking oil from pressed seeds, so both descriptions are probably justified.

Among the several lettuce types, most of which are consumed as raw leaves, one is used for its stem instead of its leaves. This lettuce is depicted on the walls of tombs dating back to about 2500 B.C.E., during the Middle Kingdom of ancient Egypt. Lettuce is shown as a long stem with marks indicating where leaves had been removed. At the top of the stem is a tuft of elongated leaves, bluish green in color. This lettuce may have been the one that first was eaten and may have been derived in turn from the type used for seed oil. The blue color is associated with the process in the growth of lettuce called bolting or stem formation. Leaves that form in the development of the head are green. As the process of bolting begins, the leaves become bluish green, signaling the elongation of the stem, which emerges from the interior of the head and eventually produces many small, yellow flowers that mature into small, narrow fruits. The fruits are less than four millimeters long. They look like seeds and usually go by that name.

Oilseed lettuce is a primitive, wild-looking plant that forms no head or rosette of leaves. It bolts early in its growth cycle, forming a thin stem with elongated, narrow leaves. The seeds produced on this stem are about 50 percent larger than those formed on cultivated lettuce. The seeds are pressed to express an oil used in cooking. This is an ancient custom still practiced in twenty-first century Egypt.

Evolution of Lettuce

One can speculate that somewhere in time ancient Egyptians selected, perhaps from oilseed lettuce, plants that bolted more slowly and formed a thick stem that was less bitter than the more primitive type and therefore edible. This new stem lettuce also had somewhat broader leaves. Later, perhaps many centuries later, further selection may have yielded a newer form with a still shorter stem and broader leaves that were appealing enough to eat, the romaine type. From Egypt, romaine lettuce moved around the Mediterranean Sea and to the Middle East. In these areas it was the most commonly grown lettuce in the twenty-first century. The original stem type traveled eastward, eventually reaching China. Numerous mentions of lettuce in ancient literature, beginning with Herodotus in 550 B.C.E., document its travels into Persia, Greece, Rome, and Sicily and later into France, Germany, and England. Use of descriptive names, such as crispa and purpurea, and place names, such as Cappadocian and Cyprian, indicate further proliferation into various distinctive types differing in color, size, leaf shape, and adaptation to specific environments. The various modern butterhead, leaf, and crisphead forms undoubtedly were selected and developed as lettuce spread through Europe. Lettuce reached the shores of the New World with the second voyage of Christopher Columbus in 1494. Many varieties within the different types were brought to the Western Hemisphere in subsequent years.

The scientific name of lettuce is Lactuca sativa. Lactuca means 'milk forming', sativa means 'common'. It is related to over one hundred wild species of Lactuca and also to sunflower, artichoke, aster, and chrysanthemum. Among the modern types of lettuce are two crisphead forms, iceberg, which forms a large, firm head, and Batavia, which is slightly softer and smaller than iceberg and is popular in Europe. Romaine lettuce has long leaves in a loaf-shaped head. Butterhead lettuce is quite small with oily, soft textured leaves. Red and green leaf lettuces form no head and have leaves with a variety of shapes. Less commonly found are the Latin type, which looks like a small romaine, and the aforementioned stem and oilseed lettuces.

Preparing a Salad

Since lettuce is used mainly in salads, preparation methods are simple, rapid, and informal. The ubiquitous tossed salad is made of lettuce leaves cut up into various-sized pieces. To some people the use of a knife is anathema, and they tear the leaves by hand. The salad maker may use one type of lettuce alone or a mixture of two or more kinds. Depending upon the ingenuity of the salad maker and the availability of edibles, any combination of other vegetables, fruits, and even cheeses or meats can be added to the lettuce. A dressing is added, and the ingredients are mixed together. Salads are vital to many slimming diets, the effectiveness of which can be reinforced or negated by the calorie value of the chosen dressing.

In the United States head lettuce was for many years commonly cut and served as a wedge, covered with mayonnaise or another dressing, and eaten with a knife and fork. This simple salad was served less frequently by the beginning of the twenty-first century. The popular Caesar salad is made only with leaves of romaine lettuce tossed with a special dressing, including a raw egg and small pieces of anchovy. A relative newcomer to the salad scene is mesclun, a mixture of baby leaves consisting of several lettuce types and other leafy vegetables, some of which are fairly exotic. These may include arugula or rocket, actually a partially domesticated weed; a fine-leaved endive called frisée; mizuna, a small, dark green round leaf from Japan; spinach, beet tops, or chard; red chicory (radicchio); and romaine, butterhead, and red and green leaf lettuces. These leaves are cut in the field by hand, or mowed, when they are no more than ten centimeters long. In parts of the American Southwest wilted lettuce is a favorite salad made by pouring bacon fat over lettuce leaves.

Some salads consist primarily of other vegetables or fruits, such as sliced tomatoes or a scoop of cottage cheese. These are often arranged in a more formal manner than a tossed salad. Lettuce may find its way into these salads as whole or shredded leaves serving as a base for the main constituent.

Lettuce may also be used to make soup, as part of the filling for sandwiches, or as a wrap for holding cooked meat and vegetable mixes. Stem lettuce is consumed raw, like a stalk of celery, in Egypt or as a cooked vegetable in China.

The Biological Human Connection

Lettuce relates to human biology in several ways. The most obvious way is in its role as a food. Some less well-known relationships to human consumption also exist.

As a green vegetable, lettuce contains many of the same nutrients found in other green vegetables, although mostly in lesser amounts. These include vitamins, minerals, water, and fiber but essentially no protein or fat (Table 1). Lettuce is a low to moderate source of vitamins and minerals. Among the various types of lettuce, romaine and leaf varieties exceed crisphead and butter-head varieties for most of the common nutrients. This is directly related to the proportion of dark green leaves in the edible portion. The nutrient contribution of lettuce compared to other vegetables is affected by the amount consumed. For example, a study by M. A. Stevens in 1974 showed that broccoli has considerably more vitamins and minerals than lettuce but that much more lettuce was consumed than broccoli; therefore the total contribution of nutrients to the diet by lettuce was greater than that of broccoli. This relationship may have changed somewhat as consumption habits changed. Nonetheless lettuce is important for its nutrient content, which complements its usefulness as a diet food because of its high water and fiber content.

Table 1

Prevention of Cancer

Research in recent years has identified a connection between the consumption of vegetables and certain other foods and beverages and anticarcinogenic activity due to the presence of compounds known as antioxidants. These compounds inhibit the formation of carcinogenic substances in the body. Among the antioxidant compounds in lettuce are 0-beta-carotene, a precursor to Vitamin A, and anthocyanin, which gives the red color in certain lettuce varieties.

The oil pressed from large seeds of certain primitive types of lettuce contributes to a minor food use. The oil is used for cooking and is similar to other oils used for the same purpose. This practice is believed to be hundreds, perhaps thousands of years old.

Nonfood Uses of Lettuce

Turning to nonfood uses, the stems and leaves of lettuce and its wild relatives contain a milky liquid called latex. The latex contains two substances called sesquiterpene lactones, which are the active ingredients in preparations used in some western European countries as a sedative and as a sleep inducer. In folk medicine additional uses for lettuce extracts include treatment for coughs, nervousness, tension, pain, rheumatism, and even insanity. The efficacy of these treatments is not well documented, but some of these effects have been shown in mice and toads.

Another minor nonfood use is drying lettuce leaves for the production of cigarettes without tobacco. Actually leaves of a wild relative of lettuce produce a more tobacco-like appearance. These have been manufactured for use in several brands of cigarettes. Effects on health are not known.

Rarely lettuce may impact human biology in a harmful way. Green leafy vegetables are normally the standard for healthful food, providing vitamins and minerals in a fresh, tasty, and light context. Nitrogen is a vital constituent of chlorophyll, the plant substance that gives the green color and controls photosynthesis. However, green leafy vegetables, including lettuce and spinach, when grown under low light and low temperature conditions in greenhouses in the winter, may accumulate high levels of the nitrate form of nitrogen. In the body nitrate may be converted to compounds that may cause the syndrome called blue baby in infants or may be carcinogenic. Fortunately the likelihood of these consequences is remote, since nitrate accumulation in greenhouse-grown lettuce can be prevented by growing the crop with adequate heat and with supplemental light. Lettuce grown outdoors is not subject to this problem.

Symbolism: Fresh, Cool, Green

The obvious symbolism associated with lettuce is three words, "fresh," "cool," and "green." "Fresh" is a word that many think of as important to health. Lettuce is eaten fresh and raw. In the gardening months many can cut it and eat it almost immediately. It is not that fresh in the store bin of course, but it is still only a few days old. Even the leaves in a packaged salad were growing in the soil shortly before they appeared on the shelf. Lettuce is never frozen or canned.

Lettuce is kept cool. After being cut in the field it is transported to a cooler, where the temperature is quickly reduced to just one degree above freezing. It is transported in refrigerated trucks to a market, where it is kept in a cooler before being placed in a refrigerated bin. Finally, it is purchased by the consumer, taken home, and placed in the refrigerator. This sequence is called the cold chain and is designed to maintain the quality of the lettuce at the time of harvest in the field as long as possible.

Finally, lettuce comes in various shades of green. Even red lettuce contains chlorophyll, which confers the green color, though it may be hidden in the red parts of the leaf. Green means vitamins. Green is a cool color. Many also associate greenness with the health of the planet and with personal health. The process of photosynthesis produces oxygen and sugar converted from carbon dioxide and water. The absorption of carbon dioxide by green plants, from lettuce to trees, helps prevent its accumulation in the air, thus mitigating the greenhouse effect and possible global warming.

The symbolism of these words is so strong that they and similar words, such as "ice," "crisp," "winter," and "spring," have been used repeatedly in various combinations in the names of lettuce varieties. Consider the names Green Ice, Iceberg, Crisp as Ice, Coolguard, Green Towers, Valverde, Valspring, and Winterset.

In ancient Egypt lettuce had sexual symbolism. After completing its vegetative development with the formation of a head or a rosette of leaves, the plant goes into its reproductive phase with the formation of an erect seed stalk bearing flowers. The amount of latex in the plant increases and is under pressure, so if the top of the flowering stalk is cut off, the latex spurts out in a manner reminiscent of ejaculation. The same tomb paintings portraying the ancient stem lettuce also picture the god Min with an erect phallus. Consumption of lettuce may therefore have been thought to increase sexual prowess.

Commercial Production and Marketing

Lettuce has become a major player in commercial production and marketing. Total production worldwide does not compare with the major cereal crops, especially rice, corn, and wheat, or with other commodities, such as sugar crops, beans, and potatoes, but among the vegetables it ranks high. In the United States it is in the top three with tomatoes and potatoes. The key word in contemporary use of lettuce is change: in use of the various types, in development of world markets, in methods of marketing, and in methods of production.

The primary markets for lettuce were, until the late twentieth century, in western Europe and North America, the consequence of its first appearance in the Mediterranean basin followed by movement into northern Europe and then to the New World. In the late twentieth century lettuce became important in Japan, China, Hong Kong, Australia, and some countries of South America and Africa. In the different regions where lettuce was consumed, one type was usually more popular than the others. In northern Europe, for example, the butterhead type predominated. Until the 1970s about 80 percent of the lettuce consumed in England was butterhead, and the other 20 percent was divided among the other major types. In the countries surrounding the Mediterranean nearly all the lettuce was romaine. Stem lettuce was the main type in Egypt and China. In the United States, until the early part of the twentieth century, no one type was strongly dominant. At that time crisphead lettuce began to increase in popularity at the expense of the other types. After the modern iceberg lettuce was developed in the 1940s, 95 percent of the production and consumption was of this type. The first modern iceberg variety was created by T. W. Whitaker of the United States Department of Agriculture and was named Great Lakes, although it was actually bred in California.

Changes in Consumption Patterns

In the late 1970s and early 1980s changes in consumption patterns began. In Britain and Scandinavia iceberg lettuce increased in popularity until it became the dominant type. Iceberg lettuce also made inroads into the butterhead and romaine domains in other western European countries. In the United States, where the iceberg type reigned supreme for most of the twentieth century, romaine, butterhead, and leaf lettuces regained popularity and comprised about one-third of the total production at the end of the twentieth century.

The construction of a home-cooked meal has become a casualty of the modern fast-paced lifestyle. People either eat out more frequently or rely on food packages that are partially processed and therefore can be prepared quickly. Salads are included in this drive for efficiency and speed. Modern supermarkets have dedicated extensive shelf space to packaged salads containing what appears to be an infinite number of combinations of leaves (lettuce, cabbage, radicchio, spinach), cut vegetables (carrots, broccoli, cauliflower), dressings, bacon bits, shredded cheeses, croutons, cut fruits, and more.

Changes have also occurred in production methods. Growing, harvesting, and marketing of lettuce is mainly on a large scale, from planting, with significant inputs of water, chemical fertilizers, and appropriate pesticides, to harvesting, cooling, and shipment to market. Production of food with organic methods has become a rapidly growing industry although it is still a small part of the production picture. Lettuce is included in this cultural change. Most of the change has been in the production of nonheading types, such as romaine and leaf lettuce, but some iceberg lettuce is grown in this way. Organic production emphasizes nonuse of chemical fertilizers and pesticides. This type of production began with small-scale growers, but has been included by growers in large-scale production systems.

Where Lettuce Is Grown

The need for coolness is a key factor in the location and magnitude of lettuce production areas. In the early twenty-first century the United States was by far the largest producer of lettuce in the world (Table 2). However, few of the fifty states produce lettuce commercially, and of the ones that do California and Arizona are responsible for over 90 percent of the production in the country. California alone accounts for over 70 percent and actually grows lettuce year-round. In the summer lettuce is produced in coastal valleys near the Pacific Ocean, particularly in the Salinas Valley, which is the most important production region in the world. In the winter lettuce is produced in the desert regions of California and Arizona. For short periods in the spring and fall lettuce is grown in the great Central Valley of California. The coolness of the season is the reason for the movement from location to location. Lettuce grows best when the daytime temperature rarely exceeds 70 to 75°F (21 to 24°C). The desert and inland areas are too hot in summer, while the coastal areas are too cold in winter. Those locations and others with similar seasonal climates in other countries, such as eastern portions of England, the Mediterranean Coast, the Negev Desert in Israel, and the southeastern portions of Australia, produce nearly all the commercially grown lettuce in the world.

Table 2

Lettuce is grown in home gardens worldwide. In warm climates lettuce growing is usually restricted to the spring and fall, when temperatures are more moderate than in summer or winter. Lettuce grows fast and is easy to grow, especially leaf lettuces, which are the ones most commonly found in the backyard garden.

Bibliography

Cao, G., E. Sofic, and R. L. Prior. "Antioxidant Capacity of Tea and Common Vegetables." Journal of Agricultural and Food Chemistry 44 (1996): 3426–3431.

Gonzalez-Lima, F., A. Veledon, and W. L. Stiehil. "Depressant Pharmacological Effects of a Component Isolated from Lettuce, Lactuca sativa L." International Journal of Crude Drug Research 24 (1986): 154–166.

Harlan, J. "Lettuce and the Sycomore: Sex and Romance in Ancient Egypt." Economic Botany 40 (1986): 4–15.

Martin, Franklin W., and Ruth M. Ruberté. Edible Leaves of theTropics. Mayagüez, Puerto Rico: Agency for International Development, Department of State, and Department of Agriculture–Agricultural Research Service, 1975.

Reinink, K., and R. Groenwold. "The Inheritance of Nitrate Content in Lettuce (Lactuca sativa L.)." Euphytica 36 (1987): 733–744.

Rubatzky, Vincent E., and Mas Yamaguchi. World Vegetables:Principles, Production, and Nutritive Values. 2d ed. New York: Chapman and Hall, 1997.

Ryder, E. J. Lettuce, Endive, and Chicory. New York: CABI, 1999.

Said, S. A., H. A. El Kashef, M. M. El Mayar, and O. Salama. "Phytochemical and Pharmacological Studies in Lactuca sativa Seed Oil." Fitoterapia 67 (1996): 215–219.

Stevens, M. A. "Varietal Influence on Nutritional Value." In Nutritional Qualities of Fresh Fruits and Vegetables, edited by Philip I. White and Nancy Selvey. Mount Kisco, N.Y.: Futura, 1974.

Sturtevant, E. Lewis. Sturtevant's Edible Plants of the World, edited by U. P. Hedrick. New York: Dover, 1972.

Whitaker, T. W. "Lettuce: Evolution of a Weedy Cinderella." Hortscience 9 (1974): 512–514.

—Edward J. Ryder

n.

An herb of the genus Lactuca, "Wherewith," says that pious gastronome, Hengist Pelly, "God has been pleased to reward the good and punish the wicked. For by his inner light the righteous man has discerned a manner of compounding for it a dressing to the appetency whereof a multitude of gustible condiments conspire, being reconciled and ameliorated with profusion of oil, the entire comestible making glad the heart of the godly and causing his face to shine. But the person of spiritual unworth is successfully tempted to the Adversary to eat of lettuce with destitution of oil, mustard, egg, salt and garlic, and with a rascal bath of vinegar polluted with sugar. Wherefore the person of spiritual unworth suffers an intestinal pang of strange complexity and raises the song."

LearnThatWord.com is a free vocabulary and spelling program where you only pay for results!

Lettuce is a slang word for money. Depending on the dreamer's association with this symbol, the dream may indicate fruitfulness or financial matters.

• Money, Currency, and Denominations - lettuce: Slang. paper currency, greenbacks

Lettuce
Iceberg lettuce field
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Asterids
Order:	Asterales
Family:	Asteraceae
Genus:	Lactuca
Species:	L. sativa
Binomial name
Lactuca sativa L.
Synonyms[1][2]
Lactuca scariola var. sativa (Moris) L. scariola var. integrata (Gren. and Godr.) L. scariola var. integrifolia (G.Beck)

Lettuce (Lactuca sativa) is a temperate annual or biennial plant of the aster or sunflower family Asteraceae. It is most often grown as a leaf vegetable, but also sometimes for its stem and seeds. Lettuce was first cultivated by the Egyptians, who turned it from a weed whose seeds were used to make oil into a plant grown for its leaves. It then spread to the Greeks and Romans, who gave it the name "lactuca", from which the modern "lettuce" ultimately derives. By 50 AD, multiple types were described, and it appeared often in medieval writings, including several herbals. The 16th through 18th century saw the development of many varieties in Europe, and by the mid-18th century varieties were being described that can still be found in gardens in the 21st century. 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.

Generally grown as a hardy annual, lettuce is easily cultivated, although it requires relatively low temperatures to prevent it from quickly flowering. It can be plagued with 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 Lactuca genus, and although this trait can be a problem to home gardeners attempting to save seeds, biologists have used it to broaden the gene pool of cultivated lettuce varieties. World production of lettuce and chicory for calendar year 2010 stood at 23,620,000 metric tons (23,250,000 long tons; 26,040,000 short tons), with over half coming from China.

Lettuce is most often used for salads, although it is also seen in other kinds of food, such as soups, sandwiches and wraps. One type is grown for its stems, which are eaten either raw or cooked. Lettuce is a good source of vitamin A and potassium, as well as minor source for several other vitamins and nutrients. Despite its beneficial properties, lettuce has often been targeted as the cause for bacterial, viral and parasitic outbreaks in humans, including E. coli and Salmonella. In addition to its main use as a leafy green, it has also gathered religious and medicinal significance over centuries of human consumption.

Contents 1 Taxonomy and etymology 2 Description 3 History 4 Cultivation 4.1 Cultivars 4.2 Cultivation problems 5 Production 6 Culinary use 7 Nutrition and health 7.1 Food-borne illness 7.2 Medicinal lore 8 References 9 Cited literature 10 External links

Taxonomy and etymology

L. sativa seeds

Lactuca sativa is a member of the Lactuca (lettuce) genus and the Asteraceae (sunflower or aster) family.^[3] The species was first described in 1753 by Carl Linnaeus in the second volume of his Species Plantarum.^[4] Synonyms for L. sativa include Lactuca scariola var. sativa,^[1] L. scariola var. integrata and L. scariola var. integrifolia.^[5] 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.^[6] Lettuce is closely related to several Lactuca species from southwest Asia, with the closest relationship being to L. serriola, an aggressive weed found in much of the world.^[7]

The Romans referred to lettuce as lactuca (lac meaning milk in Latin), which is now used as the genus name, due to the white substance exuded by cut stems.^[8] This word has become the genus name, while sativa (meaning "common") was added to create the species name.^[9] The current word "lettuce", originally from Middle English, came from the Old French letues or laitues, which derived from the Roman name.^[10] The name for cos lettuce came from the earliest European seeds of the type coming from the Greek island of Cos, a center of lettuce farming in the Byzantine period, while the name romaine came from its use in the Roman papal gardens.^[11]

Description

Mature lettuce flower and fruits

Lettuce's native range spreads between the Mediterranean and Siberia, although it has since been transported to almost all areas of the world. Plants generally have a height and spread of 6 to 12 inches (15 to 30 cm).^[12] The leaves are colorful, ranging mainly through the green and red color spectrums, with some variegated varieties.^[13] There are also a few varieties with yellow, gold or blue-teal leaves.^[14] They have a wide range of shapes and textures, from the dense heads of iceberg lettuce to the notched, scalloped, frilly or ruffly leaves of leaf lettuces.^[13] Lettuce plants have a root system that includes a main taproot and smaller secondary roots. Some varieties, especially those found in the US 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.^[14]

Depending on the variety and time of year, lettuce generally lives 65–130 days from planting to harvesting. Because lettuce that flowers (called "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.^[15] Once plants move past the eating stage, they develop flower stalks up to 3 feet (0.9 m) high with small yellow blossoms.^[16] Lettuce flowers are composed of multiple florets, each containing a ligulate petal and reproductive system. This system includes fused anthers that form a tube surrounding a bipartite stigma-containing style. As the anthers shed pollen, the style elongates to allow the stigmas, now coated with pollen, to emerge from the tube.^[14] The flowers 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. 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; these include slower bolting, larger seeds, larger leaves and heads, better taste and texture, a lower latex content, and different leaf shapes and colors. Work in several of these areas continues through the present day.^[17] Scientific research into the genetic modification of lettuce is ongoing, with over 85 field trials in progress 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 the commercial agriculture setting.^[18]

History

Lettuce developed from a weedy plant found in Egypt, first used for the production of oil from its seeds. This plant was probably selectively bred by the ancient Egyptians into a plant grown for its edible leaves,^[19] with evidence of its cultivation appearing as early as 2680 BC.^[8] 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."^[20] Its use in religious ceremonies resulted in many images being created in tombs and wall paintings. The variety under cultivation by the Egyptians appears to have been about 30 inches (76 cm) 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 these may have been ancestors of today's lettuces.^[8]

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

Lettuce appears in many medieval writings, especially with regards to its use 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.^[11] Lettuce was first brought to the Americas from Europe by Christopher Columbus in the late 15th century.^[21][22] 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 still found in gardens today.^[23]

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 United States, of changing the name of a variety 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 showed there to be somewhere 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.^[24] 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 more closely resembles tobacco.^[25]

Cultivation

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.^[23] 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 8 to 14 inches (20 to 36 cm) 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.^[16]

A transplanted bed of lettuce in a greenhouse

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 75 °F (24 °C); cool temperatures prompt better performance, with 60 to 65 °F (16 to 18 °C) being preferred and as low as 45 °F (7 °C) being tolerated. Plants in hot areas that are provided partial shade during the hottest part of the day will bolt more slowly. Temperatures above 80 °F (27 °C) will generally result in poor or non-existent germination of lettuce seeds.^[26] After harvest, lettuce lasts the longest when kept at 32 °F (0 °C) 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.^[27]

Lettuce varieties will cross with each other, making spacing of 5 to 20 feet (1.5 to 6.1 m) between varieties necessary to prevent contamination of varieties 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.^[16] 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.^[28] Seeds keep best when stored in cool conditions, and, unless stored cryogenically, remain viable the longest when stored at −4 °F (−20 °C); 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.^[29]

Cultivars

A selection of lettuce cultivars

There are several types of lettuce, but three (leaf, head and cos or romaine) are the most common.^[26] There are seven main cultivar groups of lettuce, each including many varieties:

• Leaf – Also known as looseleaf, cutting or bunching lettuce,^[30] this type has loosely bunched leaves and is the most widely planted. It is used mainly for salads.^[27]
• Romaine/Cos – Used mainly for salads and sandwiches, this type forms long, upright heads.^[27] This is the most often used lettuce in Caesar salads.^[21]
• Crisphead – Better known as the "iceberg" lettuce, the most popular lettuce in the United States, this type is very heat-sensitive and was originally adapted for growth in the northern US. It ships well, but is low in flavor and nutritional content, being composed of even more water than other lettuce types.^[27]
• Butterhead – Also known as Boston or Bibb lettuce,^[30] this type is a head lettuce with a loose arrangement of leaves, known for its sweet flavor and tender texture.^[27]
• 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.^[30]
• 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.^[27]
• 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.^[31]

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.^[32]

Cultivation problems

See also: List of lettuce diseases

A lettuce surrounded by weeds, which have crowded it to the point of bolting

Nutrient deficiencies, including a lack of boron, phosphorus, calcium, molybdenum or copper, can cause a variety of plant problems that range from malformed plants to a lack of head growth.^[26] Many insects are attracted to lettuce, including cutworms, which cut plants 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. Mammals, including rabbits and groundhogs, also eat the plants.^[33] 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 identifying and producing varieties with larger amounts of these compounds for increased pest resistance.^[34]

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.^[33] Crowding lettuce tends to attract pests and diseases.^[16] 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.^[35] Herbicides are often used to control weeds in commercial production. However, this has led to the development of herbicide-resistant weeds, as well as generating environmental and health concerns.^[17]

Production

Lettuce is the only member of the Lactuca genus to be grown commercially.^[36] The Food and Agriculture Organization of the United Nations (FAO) reports that world production of lettuce and chicory for calendar year 2010 was 23,622,366 metric tons (23,249,287 long tons; 26,039,201 short tons), coming primarily from China (53 percent), United States (17 percent) and India (4 percent).^[37]

Top ten lettuce and chicory producers — 2010

Country	Production (tonnes)	Source
People's Republic of China	12,574,500	FAO estimate
United States	3,954,800	official figure
India	998,600	FAO estimate
Italy	843,344	official figure
Spain	809,200	official figure
Japan	537,800	official figure
Iran	402,800	FAO estimate
France	398,215	official figure
Turkey	358,096	official figure
Mexico	340,976	official figure
World	23,622,366	aggregate
Source: Food And Agricultural Organization of United Nations: Economic And Social Department: The Statistical Division

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 United States, 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.^[38] As of 2007, 70 percent of the lettuce production in the US comes from California; in that country it ranks third in produce consumption behind tomatoes and oranges.^[39]

Changes in lettuce production methods, including all of the processes from growing to sales, have become much larger in scale during the 20th century. The majority of agricultural production is done with the application of large amounts of chemicals, including fertilizers and pesticides, but large-scale organic production makes up a growing percentage of the market – a trend that began with small growers but moved to a more industrial scale. More non-heading types, mostly leaf and romaine lettuces, are also being grown.^[38]

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.^[8] 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.^[19] 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.^[9]

Nutrition and health

Lettuce (butterhead)

Nutritional value per 100 g (3.5 oz)
Energy	55 kJ (13 kcal)
Carbohydrates	2.2 g
- Dietary fibre	1.1 g
Fat	0.2 g
Protein	1.4 g
Water	96 g
Vitamin A equiv.	166 μg (21%)
Folate (vit. B9)	73 μg (18%)
Vitamin C	4 mg (5%)
Vitamin K	102 μg (97%)
Iron	1.2 mg (9%)
Potassium	238 mg (5%)
Percentages are relative to US recommendations for adults. Source: USDA Basic Report – Lettuce, butterhead

Depending on the variety, lettuce is a good source of vitamin A and potassium, with higher concentrations of vitamin A found in darker green lettuces. It also provides some dietary fiber (concentrated in the spine and ribs), carbohydrates, protein and a small amount of fat. With the exception of the iceberg type, lettuce also provides some vitamin C, calcium, iron and copper, with vitamins and minerals largely found in the leaf.^[27]

Food-borne illness

Although most food-borne pathogens can survive on stored lettuce, they tend to decline in number during the storage period. The exception to this is Listeria monocytogenes, the causative agent of listeriosis, which multiplies in storage. However, despite very high levels of the bacteria being found on ready-to-eat lettuce products, a 2008 study found no incidences of food-borne illness related to listeriosis. The researcher posited that this may be due to the product's short shelf life, indigenous microflora competing with the Listeria bacteria, or possible properties within the lettuce that cause the bacteria to be unable to cause listeriosis.^[40]

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, which have been found mainly in lettuce.^[41] 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.^[42] Salmonella bacteria, including the uncommon Salmonella braenderup type, have also caused outbreaks traced to contaminated lettuce.^[43] 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.^[41]

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^[38] and a promotor of love and childbearing in women, and the Romans likewise claimed that it increased sexual potency.^[44] In contrast, the ancient Greeks connected the plant with male impotency^[8] and served it during funerals (probably due to its role in the myth of Adonis's death), and British women in the 1800s believed it would cause infertility and sterility. Lettuce has mild narcotic properties – it was called "sleepwort" by the Anglo-Saxons due to this attribute – although the cultivated L. sativa has lower levels of the narcotic than its wild cousins.^[44] This narcotic effect is a property of two sesquiterpene lactones, located in the white liquid in the stems of lettuce, called latex.^[25]

Lettuce extracts are sometimes used in skin creams and lotions for treating sunburn and rough skin. It was once thought to be useful in relieving liver issues. Some American settlers claimed that smallpox could be prevented through the ingestion of lettuce,^[44] and an Iranian belief suggested consumption of the seeds when afflicted with typhoid.^[45] 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, although similar effects have been demonstrated in mice and toads.^[25] 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.^[46]

References

1. ^ ^{a b c d} "Lactuca sativa". Kew Royal Botanical Gardens. http://www.kew.org/science-research-data/kew-in-depth/difficult-seeds/species-profiles/lactuca-sativa/index.htm. Retrieved 2012-04-02. 
2. ^ ^{a b} "Lactuca serriola L". United States Department of Agriculture. http://plants.usda.gov/java/profile?symbol=LASE. Retrieved 2012-04-02. 
3. ^ "Lactuca sativa L". Integrated Taxonomic Information System. http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=36607. Retrieved 2010-03-27. 
4. ^ "The Linnaean Plant Name Typification Project". Natural History Museum. http://www.nhm.ac.uk/research-curation/research/projects/linnaean-typification/database/detail.dsml?ID=492400&listPageURL=list.dsml%3FCSpecies%3Dsativa%26CGenus%3DLactuca. Retrieved 2012-04-02. 
5. ^ "Lactuca sativa L". United States Department of Agriculture. http://plants.usda.gov/java/profile?symbol=LASA3. Retrieved 2012-04-02. 
6. ^ Porcher, Michael H. (2005). "Sorting Lactuca Names". Multilingual Multiscript Plant Name Database. University of Melbourne. http://www.ars-grin.gov/misc/mmpnd/Lactuca.html. Retrieved 2012-04-02. 
7. ^ Zohary, Daniel; Hopf, Maria; Weiss, Ehud (2012). Domestication of Plants in the Old World: The Origin and Spread of Domesticated Plants in Southwest Asia, Europe, and the Mediterranean Basin. Oxford University Press. ISBN 0-19-954906-0. http://books.google.com/books?id=1hHSYoqY-AwC&pg=PA157#v=onepage&q&f=false. 
8. ^ ^{a b c d e} Weaver, pp. 170–172
9. ^ ^{a b} Katz and Weaver, p. 376
10. ^ Chantrell, Glynnis, ed. (2002). The Oxford Dictionary of Word Histories. Oxford University Press. p. 300. ISBN 0-19-863121-9. 
11. ^ ^{a b} Weaver, p. 172
12. ^ "Lactuca sativa". Missouri Botanical Garden. http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/plant-finder/plant-details/kc/a679/lactuca-sativa.aspx. Retrieved 2012-03-27. 
13. ^ ^{a b} Fine Cooking Magazine (2011). Fine Cooking in Season: Your Guide to Choosing and Preparing the Season's Best. Taunton Press. p. 28. ISBN 1-60085-303-X. http://books.google.com/books?id=eAyNxv2I1LoC&pg=PA28&dq=lettuce+leaf+color+range&hl=en&sa=X&ei=cMSFT6a4DoWdgwedn9nQBw&ved=0CEUQ6AEwAA#v=onepage&q=lettuce%20leaf%20color%20range&f=false. 
14. ^ ^{a b c} Ryder, J. and Waycott, Williams (1993). "New Directions in Salad Crops: New Forms, New Tools, and Old Philosophy". In Janick, J and Simon J.E. New Crops. Wiley. pp. 528–532. http://www.hort.purdue.edu/newcrop/proceedings1993/v2-528.html. 
15. ^ 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. http://ucanr.org/freepubs/docs/7216.pdf. Retrieved 2012-04-11. 
16. ^ ^{a b c d} Weaver, pp. 175–176
17. ^ ^{a b} Davey, et al., pp. 222–225
18. ^ "Lettuce". GMO Compass. http://www.gmo-compass.org/eng/database/plants/65.lettuce.html. Retrieved 2012-04-03. 
19. ^ ^{a b} Katz and Weaver, pp. 375–376
20. ^ Hart, George (2005). The Routledge Dictionary of Egyptian Gods and Goddesses (2nd ed.). Routledge. p. 95. ISBN 1-134-28424-1. http://books.google.com/books?id=Q1LAiPylZm4C&pg=PA95&lpg=PA95&dq=lettuce+in+egyptian+ritual&source=bl&ots=4itqEJFLXw&sig=5GSUfBm5sU_QcVOXMrQNtlY9S5Y&hl=en&sa=X&ei=Dw97T9OALYXyggewivGAAw&ved=0CB4Q6AEwAA#v=onepage&q=lettuce%20in%20egyptian%20ritual&f=false. 
21. ^ ^{a b} "Vegetable of the Month: Lettuce". Centers for Disease Control and Prevention. http://www.fruitsandveggiesmatter.gov/month/lettuce.html. Retrieved 2012-03-26. 
22. ^ Subbarao, Krishna V. and Koike, Steven T. (2007). "Lettuce Diseases: Ecology and Control". In Pimentel, David. Encyclopedia of Pest Management, Volume 2. CRC Press. p. 313. ISBN 1-4200-5361-2. http://books.google.com/books?id=DxrMm9lMFUAC&pg=PA313&dq=Christopher+Columbus+lettuce+new+world&hl=en&sa=X&ei=Od9wT9fwDsiviAKBn9WBDQ&ved=0CDAQ6AEwAA#v=onepage&q=Christopher%20Columbus%20lettuce%20new%20world&f=false. 
23. ^ ^{a b} Weaver, pp. 172–173
24. ^ Weaver, pp. 173–174
25. ^ ^{a b c} Katz and Weaver, p. 377
26. ^ ^{a b c} Bradley, p. 129
27. ^ ^{a b c d e f g} "Lettuce". University of Illinois Extension. http://urbanext.illinois.edu/veggies/lettuce.cfm. Retrieved 2012-03-25. 
28. ^ Koopman, Wim J.M.; Guetta, Eli; van de Wiel, Clemens C.M.; Vosman, Ben; van den Berg, Ronald G (1998). "Phylogenetic relationships among Lactuca (Asteraceae) species and related genera based on ITS-1 DNA sequences". American Journal of Botany 85 (11): 1517–1530. doi:10.2307/2446479. JSTOR 2446479. PMID 21680311. http://www.amjbot.org/cgi/content/full/85/11/1517. 
29. ^ Davey, et al., p. 241
30. ^ ^{a b c} Miles, Carol. "Winter Lettuce". Washington State University. http://vegetables.wsu.edu/winterlettuce.html. Retrieved 2012-03-26. 
31. ^ Katz and Weaver, p. 375
32. ^ Larkcom, Joy and Phillips, Roger (2003). The Organic Salad Garden. Frances Lincoln Ltd. p. 12. ISBN 0-7112-2204-5. http://books.google.com/books?id=SsQ8XBJkGG8C&pg=PA12&lpg=PA12&dq=crisphead+cabbage+lettuce&source=bl&ots=z5omQjsCMN&sig=QBlnrfme9WNR8FuDMO9ddVwNxjc&hl=en&sa=X&ei=8upwT_PKIfDViALb9dyzDA&ved=0CDsQ6AEwBA#v=onepage&q=crisphead%20cabbage%20lettuce&f=false. 
33. ^ ^{a b} Bradley, pp. 129–132
34. ^ "Developing Multi-Species Insect Resistance in Romaine Lettuce". United States Department of Agriculture. http://www.reeis.usda.gov/web/crisprojectpages/198636.html. Retrieved 2012-04-05. 
35. ^ "Lettuce: Integrated Weed Management". UC Pest Management Guidelines. University of California. August 2007. http://www.ipm.ucdavis.edu/PMG/r441700111.html. Retrieved 2012-04-03. 
36. ^ Koike, Steven T; Gladders, Peter; Paulus, Albert O. (2006). Vegetable Diseases: A Color Handbook. Gulf Professional Publishing. p. 296. ISBN 0-12-373675-7. http://books.google.com/books?id=iPgTGhaGRl4C&pg=PA296#v=onepage&q&f=false. 
37. ^ "FAO Statistics Database". Food and Agriculture Organization of the United Nations. http://faostat.fao.org/site/567/DesktopDefault.aspx?PageID=567#ancor. Retrieved 2012-03-24. 
38. ^ ^{a b c} Katz and Weaver, p. 378
39. ^ Davey, et al., p. 222
40. ^ Hanning, I.B.; Johnson, M.G.; Ricke, S.C (December 2008). "Precut prepackaged lettuce: a risk for listeriosis?". Foodborne Pathogens and Disease 5 (6): 731–46. doi:10.1089/fpd.2008.0142. PMID 18847382. 
41. ^ ^{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. April 12, 2012. http://www.fda.gov/Food/ScienceResearch/ResearchAreas/SafePracticesforFoodProcesses/ucm091265.htm. Retrieved 2012-04-19. 
42. ^ Davis, J.G. and Kendall, P. "Preventing E. coli from Garden to Plate". Colorado State University. http://www.ext.colostate.edu/pubs/foodnut/09369.html. Retrieved 2012-03-26. 
43. ^ 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. 
44. ^ ^{a b c} Watts, Donald (2007). Dictionary of Plant Lore. Academic Press. p. 226. ISBN 0-12-374086-X. http://books.google.com/books?id=WAagnZNb0cAC&pg=PA226&dq=Medicinal+uses+of+lettuce&hl=en&sa=X&ei=4xVtT8XVOKiniQKbh6zDBQ&ved=0CF8Q6AEwBw#v=onepage&q=Medicinal%20uses%20of%20lettuce&f=false. 
45. ^ 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. http://books.google.com/books?id=UcLYLpwdcm8C&pg=PA230#v=onepage&q&f=false. 
46. ^ MacFarquhar, Neil (2003-01-03). "Bashiqa Journal: A Sect Shuns Lettuce and Gives the Devil His Due". The New York Times. http://query.nytimes.com/gst/fullpage.html?res=9B00E5DF1E3FF930A35752C0A9659C8B63&sec=&spon=&pagewanted=all. Retrieved 2012-03-23. 

Cited literature

Lettuce portal Food portal

• Bradley, Fern Marshall; Ellis, Barbara W.; Martin, Deborah L., ed. (2009). The Organic Gardener's Handbook of Natural Pest and Disease Control. Rodale, Inc. 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 3-540-36752-7. 
• Katz, Solomon H. and Weaver, William Woys (2003). Encyclopedia of Food and Culture. Volume 2. Scribner. ISBN 0-684-80565-0. 
• Weaver, Williams Woys (1997). Heirloom Vegetable Gardening: A Master Gardener's Guide to Planting, Seed Saving and Cultural History. Henry Holt and Company. ISBN 0-8050-4025-0. 

External links

• Media related to Lactuca sativa at Wikimedia Commons

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Dansk (Danish)
n. - salat, salathoved, pengeseddel

Nederlands (Dutch)
sla, kropsla

Français (French)
n. - (Bot, Culin) laitue, romaine, laitue croquante

Deutsch (German)
n. - Salat

Ελληνική (Greek)
n. - (φυτολ.) μαρούλι

Italiano (Italian)
lattuga

Português (Portuguese)
n. - alface (f) (Bot.)

Русский (Russian)
салат-латук, деньги

Español (Spanish)
n. - lechuga

Svenska (Swedish)
n. - huvudsallat, sallad, salladshuvud

中文（简体）(Chinese (Simplified))
莴苣, 苦菜类, 生菜

中文（繁體）(Chinese (Traditional))
n. - 萵苣, 苦菜類, 生菜

한국어 (Korean)
n. - 상치

日本語 (Japanese)
n. - レタス

العربيه (Arabic)
‏(الاسم) الخس نبات‏

עברית (Hebrew)
n. - ‮חסה (ירק), "ירוקים" (דולרים) (מדוברת, ארה"ב)‬

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