Root is the rhizome of reeds, reed stem is the young stem of reeds. Both from the same plant, similar efficacy. But reed root is long for the thirst, reed stem is long for the clearing of lung heat, a slight focus. There is no supply of reed stem in the medicine market, so rehmannia root can be used as a substitute. It can be divided into fresh reed root and dried reed root. Fresh reed root is also known as live water reed root. It is long cylindrical or flat cylindrical, with different lengths and a diameter of about 1.5 centimeters. The surface is yellowish-white, glossy, with the apex pointed like a bamboo shoot, green or yellowish-green. All have nodes, internodes 10-17 centimeters long, nodes with residual fibrous roots and bud scars. The texture is light and tough, not easy to break. Transverse section of yellow-white, hollow, peripheral wall thickness of about 1.5 mm, can be seen arranged into a ring of fine holes, loose outer skin, can be peeled. Gas no, taste sweet.　Dried rehmannia root is compressed long cylindrical. The surface is glossy, yellowish-white, the nodes are hard, reddish-yellow, and there are longitudinal wrinkles between the nodes. The texture is light and pliable, not easy to break, no gas, taste slightly sweet. All to strip thick, yellow-white, glossy, no need to root, the quality of tender is good.