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Romaine or cos lettuce is a variety of Greek Lettuce (Lactuca sativa L. var. longifolia) which grows in a tall head of sturdy leaves with a firm rib down the center. Unlike most lettuces, it is tolerant of heat.
Origin and etymology 
Many dictionaries trace the word cos to the name of the Greek island of Cos, from which the lettuce was presumably introduced. Other authorities trace it to the Arabic word for lettuce, خس khus ([ˈxus]).
It apparently reached the West via Rome, as in Italian it is called lattuga romana and in French laitue romaine, both meaning 'Roman lettuce', hence the name 'romaine', the common term in American English.
The thick ribs, especially on the older outer leaves, should have a milky fluid which gives the romaine the typically fine-bitter herb taste. Romaine is the usual lettuce used in Caesar salad. Romaine lettuce is commonly used in Middle Eastern cuisine.
Ritual use 
|Nutritional value per 100 g (3.5 oz)|
|Energy||72 kJ (17 kcal)|
|- Dietary fibre||2.1 g|
|Vitamin A equiv.||290 μg (36%)|
|Folate (vit. B9)||136 μg (34%)|
|Vitamin C||24 mg (29%)|
|Calcium||33 mg (3%)|
|Iron||0.97 mg (7%)|
|Phosphorus||30 mg (4%)|
|Potassium||247 mg (5%)|
|Percentages are relative to
US recommendations for adults.
Source: USDA Nutrient Database
As with other dark leafy greens, the antioxidants contained within romaine lettuce are believed to help prevent cancer. According to the 2011 edition of the Old Farmer's Almanac, the chlorophyll pigment in dark leafy greens, such as Romaine lettuce, may reduce levels of colon and liver cancer carcinogens.
- Oxford English Dictionary, First Edition, 1893, s.v. 'cos'
- "Cos lettuces are probably not named for the island of Kos but for the Arabic word for lettuce', Alan Davidson, The Oxford Companion to Food, s.v. 'lettuce'. Oxford University Press 1999. ISBN 0-19-211579-0.
- Bradshaw, Paul; Hoffman, Lawrence (August 19, 2000). "Towards a History of the Paschal Meal". Passover and Easter: Origin and History to Modern Times. University of Notre Dame Press. ISBN 9780268038595.
- American Institute for Cancer Research, "Foods That Fight Cancer: Dark Green Leafy Vegetables".
- Tooke, William. The Monarchy of France: its rise, progress, and fall, p. 634
- Kirschmann, John D. & Dunne, Lavon J. Nutrition Almanac, s.v. ISBN 0-07-034906-1.
- The dictionary definition of romaine at Wiktionary
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