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, romaine is often sold as whole heads or as "hearts" that have had the outer leaves removed and are often packaged together. Commercially sold romaine lettuce has occasionally been the subject of product warnings by both U.S. and Canadian health authorities warning that consumer supplies can become contaminated with or host pathogenic E.coli bacteria. Cattle can harbor the bacteria without ill effects, and be asymptomatic carriers of the bacterium. Lettuce becomes contaminated with the bacterium as the result of cattle manure being used to fertilize crop fields, or the proximity of cattle pastures and feedlots to water sources used to irrigate crops. Origin and etymology In North American English it is known as "romaine" lettuce and in British English the names "cos" lettuce and "romaine" lettuce are both used. 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 cos to the Arabic word for lettuce, . The first mention of cos lettuce in English dates from the late 17th century in John Evelyn's 1699 work Acetaria. A discourse of sallets. It apparently reached Western Europe via Rome, as it is called lattuga romana in Italian and in French, both meaning "Roman lettuce" – hence the name "romaine", the common term in North America. Cultural significance For 3000 years (from at least 2700 BC), lettuce was associated with the ancient Egyptian god of fertility, Min, for its resemblance to the phallus. Romaine lettuce may be used in the Passover Seder ritual feast as a type of bitter herb. It symbolises the bitterness inflicted by the Egyptians while the Israelites were slaves in Egypt. The day of 22 Germinal in the French Republican Calendar was dedicated to romaine lettuce, as "". Cuisine Romaine is a common salad green, and is the usual lettuce used in Caesar salad. Romaine lettuce is commonly used in Middle Eastern cuisine. Romaine, like other lettuces, may also be cooked. For example, it can be braised or made into soup. The thick ribs, especially on the older outer leaves, have a milky fluid that gives the romaine its typically bitter