Lettuce, (Lactuca sativa), annual leaf vegetable of the aster family (Asteraceae). Most lettuce varieties are eaten fresh and are commonly served as the base of green salads. Lettuce is generally a rich source of vitamins K and A, though the nutritional quality varies, depending on the variety.
Lettuce is a cool weather crop and is best grown in spring and fall. The seeds germinate in temperatures as low as 40 F (4 C) but its ideal germination and growing temperature is between 60 and 65 F (16 to 18 C). To grow great lettuce, find a site that offers at least six to eight hours of direct sun.