Lettuce (Lactuca sativa) is an annual vegetable belonging to the Compositae family. Several species of wild lettuce occur in Canada, including prickly lettuce, a common weed that is a probable parent species of garden lettuce. Native to Asia Minor, lettuce was introduced to Haiti by Christopher Columbus. Of the four major varieties, head lettuce, which is firm and keeps well, is the most widely grown. The other varieties include small, tender-headed Bibb lettuce, long-headed Romaine lettuce and high-quality leaf lettuce. Lettuce thrives in cool climates and is well suited to Canada's organic soils. Being frost resistant, it is usually sown in early spring. Less firm varieties are often grown in greenhouses in autumn. Slugs, aphids and leaf rot are its principal pests. Lettuce provides average food value (head lettuce being the least nutritious) and because of its freshness is a basic salad ingredient. Nearly 70 000 t of leaf lettuce and head lettuce are produced annually in Canada.