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Lettuce (plant)

December 30, 2012 by  

Lettuce (plant), Lettuce (Lactuca sativa) is an annual plant of the aster or sunflower family Asteraceae. It is most often grown as a leaf vegetable, but sometimes for its stem and seeds. Lettuce was first cultivated by the ancient Egyptians who turned it from a weed, whose seeds were used to produce oil, into a plant grown for its leaves. Lettuce spread to the Greeks and Romans, the latter of whom gave it the name “lactuca”, from which the English “lettuce” is ultimately derived.

By 50 AD, multiple types were described, and lettuce appeared often in medieval writings, including several herbals. The 16th through 18th centuries saw the development of many varieties in Europe, and by the mid-18th century cultivars were described that can still be found in gardens. Europe and North America originally dominated the market for lettuce, but by the late 1900s the consumption of lettuce had spread throughout the world.
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 6 to 12 inches (15 to 30 cm). 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.

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. The ovaries form compressed, obovate (teardrop-shaped) dry fruits that do not open at maturity, measuring 3 to 4 mm long. The fruits have 5-7 ribs on each side and are tipped by two rows of small white hairs. The pappus remains at the top of each fruit as a dispersal structure. Each fruit contains one seed, which can be white, yellow, gray or brown depending on the variety of lettuce.

The domestication of lettuce over the centuries has resulted in several changes through selective breeding: delayed bolting, larger seeds, larger leaves and heads, better taste and texture, a lower latex content, and different leaf shapes and colors. Work in these areas continues through the present day. Scientific research into the genetic modification of lettuce is ongoing, with over 85 field trials taking place between 1992 and 2005 in the European Union and United States to test modifications allowing greater herbicide tolerance, greater resistance to insects and fungi and slower bolting patterns. However, genetically modified lettuce is not currently used in commercial agriculture.

Lettuce is the only member of the Lactuca genus to be grown commercially. The Food and Agriculture Organization of the United Nations (FAO) reports that world production of lettuce and chicory (the two plants being combined by the FAO for reporting purposes) for calendar year 2010 was 23,622,366 metric tons (23,249,287 long tons; 26,039,201 short tons). This came primarily from China (53 percent), the US (17 percent) and India (4 percent). 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. Stem lettuce was first developed in China, and remains primarily cultivated in that country.

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 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. In the first years of the 21st century, bagged salad products began to hold a growing portion of the lettuce market, especially in the US. Processed from what was previously waste lettuce not considered acceptable for the fresh market, these products are packaged in a manner that makes them last longer than standard head lettuce after harvest. As of 2007, 70 percent of the lettuce production in the US came from California; in that country it ranks third in produce consumption behind tomatoes and oranges.

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