Lettuce is a general heading, like cabbage, and simply refers to many types of greens used in salads. In many languages the same word is used for lettuce as is used for green salad, lettuce representing many green salad leaves, though it should really be confined to those that leak a milky substance when the lettuce is cut. These would include Cos or Romaine lettuce as well as the butterheads. By as early as 500 BC, lettuce with no formed heads, as grew then, was already popular on the tables of Romans, where it was thought to aid digestion.
.jpg)