Lettuce (Lactuca sativa) is an easy-to-grow cool-season annual that is generally divided into four types: leaf, butterhead, and romaine (cos), and crisphead (iceberg). Leaf lettuce produces loose, open heads of ruffled leaves. Butterhead makes tight heads of soft, tender leaves. Romaine forms upright heads of firm, crisp leaves. Iceberg produces crisp, mild-flavored tight heads. All types prefer moist fertile soil & mild weather, romaine being the most tolerant of heat and the most nutritious. Lettuce is a familiar staple salad vegetable grown worldwide. It is high in vitamin A and folic acid. Direct sow in spring or autumn, or start indoors - lettuce transplants very well. Sow it thickly and eat the thinnings.