Cos lettuce

Also know as Romaine .Cos lettuce is a variety of lettuce which grows in a long head of sturdy leaves with a firm rib down the center. It is so called because it is said to have originated on the Greek island of Cos (Kos). Unlike most lettuces, it is tolerant of heat. It is a cultivar of the common lettuce (Lactuca sativa) and is distinguished by an elongated head; dark green, long, narrow, crisp, stiff leaves and a coarse texture, with a distinctive rib almost to the tip of the leaf.The thick ribs, especially on the older outer leaves, should have a milky fluid which gives the romaine the typically fine-bitter herb taste. In commercial terms, romaine is the second most important type of lettuce, iceberg lettuce being the first. The interior leaves are paler in color, and more delicate in flavor. There is also a milder tasting variety with red tipped leaves and, a sweet romaine, which is even sweeter than regular romaine.