They may have straight or hooked tips. Spines grow in clusters out of small lumps or mounds, called areoles, on the stem. Areoles occur in regular patterns on the stem. In some species, such as the saguaro and the barrel cactus, the areoles merge to form ribs that run along the length of the stem. The ribs give the plant shade and help the stem store water.
All cactuses produce flowers.
Like the spines, flowers grow out of the areoles. The flowers may be white or a bright color, such as yellow, orange, or red. In most species, the flowers are short-lived. They bloom only a few days. Some open only at night.