Cultivated annual salad plant (Lactuca sativa) that produces clusters of crisp, water-filled leaves. The best-known varieties are head, or cabbage, lettuce (variety capitata); leaf, or curled, lettuce (variety crispa); cos, or romaine, lettuce (variety longifolia); and asparagus lettuce (variety asparagina). Head lettuce is further divided into butter heads and crisp heads (e.g., iceberg lettuce). In the U.S, large-scale farms grow mainly crisp-head varieties, shipping them nationwide. Small-scale, local farmers raise leaf and butter-head varieties. Lettuce is an early annual crop that grows best in cool weather and with ample water. Though usually consumed in salads, it may also be cooked.
This entry comes from Encyclopædia Britannica Concise. For the full entry on lettuce, visit Britannica.com.