Lettuce, a hardy annual plant native to Europe and Asia. Lettuce has been cultivated for more than 2,000 years for its leaves, which are used as food, chiefly in salads. Lettuce grows to be three feet (90 cm) tall and has small, pale yellow flowers and light green to reddish-brown leaves. As a food, lettuce is low in calories but a good source of vitamin A and of minerals, including iron, calcium, and phosphorus. It also furnishes dietary fiber, which stimulates activity in the intestines and aids in the elimination of body wastes.
Because it is a cool-weather plant, lettuce should be planted in early spring in cool areas and in winter in warm areas. In hot weather lettuce tends to bolt, or go to seed. Among commercial vegetable crops grown in the United States lettuce is exceeded in value only by potatoes and tomatoes.
Four varieties of lettuce are cultivated, and there are innumerable types of each variety. The varieties are:
- Head Lettuce, which forms compact, rounded heads of leaves. A type of head lettuce with extremely compact heads of crisp leaves is called iceberg, or crisphead, lettuce. Another type, with looser heads of softer leaves, is called butterhead lettuce. An intermediate type is Bibb lettuce.
- Cos, or Romaine, lettuce, which grows elongated heads of leaves. Types include Parris Island and red romaine.
- Leaf Lettuce, which produces loose clusters of leaves. A common type is black-seeded Simpson.
- Asparagus Lettuce, grown for its thick stalks, which are prepared similarly to asparagus. Celtuce, probably a variety of asparagus lettuce, is grown for both its leaves and its stalks.
Lettuce is Lactuca saliva of the composite family, Compositae. Head lettuce is L. s. capitata; leaf, L. s. crispa; cos, L. s. longifolia; asparagus lettuce. L. s. angustana (or asparagina.)