A cool-season annual, Lactuca sativa, of Asian origin and belonging to the tribe Cichorium of the Compositae family. Lettuce is grown for its succulent leaves, which are eaten raw as a salad. Four varieties of this leading salad crop are head lettuce (L. sativa var. capitata; see illus.), leaf or curled lettuce (L. sativa var. longifolia), and stem or asparagus lettuce (L. sativa var. asparagina). There are two types of head lettuce: butterhead, and crisphead or iceberg.