Lettuce is a one- or two-year-old plant in the Asteraceae family and is fed as leaf balls or tender stems. The roots of lettuce are taproot systems with many lateral roots and well-developed fibrous roots. They are generally distributed in the soil layer 30 cm below the surface. The stem is a shortened stem. After the rosette leaves are formed, the stem includes the primary stem developed from the hypocotyl and the elongated and enlarged shoot-like stem of the flower stem. The outer skin of the stem is green, green-white, purple, purple-green, and the flesh of the stem is green, yellow-green, green-white and other colors. It varies depending on the species. The leaves are from the roots, alternate, smooth or wrinkled, green or green-purple. The flowers are in flower heads and are self-pollinated. The seeds mature 15 days after flowering. The seeds are achenes, which are small and long, gray-black or yellow-brown. When mature, there are scattered pappus on the top, which can be blown away by the wind. The weight of 1,000 seeds is 0.8 to 1.2 grams.