[Wikipedia] Plant Relatives, Response to Rainfall: While semi-succulent and a desert plant, Ocotillo is more closely related to the tea plant and blueberries than to cactuses. For much of the year, the plant appears to be an arrangement of large spiny dead sticks, although closer examination reveals that the stems are partly green. With rainfall, the plant quickly becomes lush with small (2 - 4 cm), ovate leaves, which may remain for weeks or even months. (link added by Mary Ann Machi)