When the stamen-bearing and pistil-bearing flowers are on separate trees or plants they are classed as dioecious. Examples of this class are found in the date, box-elder, and buffalo-berry. Where the staminate and pistillate flowers are separated, but on the same tree or plant, they are classed as monoecious, such as chestnut, oak, and walnut. Polygamous plants are those having both perfect flowers and those of one sex on the same or on different individuals, such as the red maple, hackberry, and elm.