A large family, widely distributed, chiefly tropical; ours are perennial herbs, with milky, bitter juice; leaves toothless, usually opposite, without stipules; flowers perfect, parts in fives; corolla united; stamens on the corolla, as many as its lobes, alternate with them, ovary superior, in two parts, united by a single or two-parted style, developing into two pods; seeds often tufted with hairs. The Greek name alludes to the superstition that these plants are poisonous to dogs.

There are many kinds of Apocynum, with branching stems, tough fibrous bark, and small, white or pink flowers, in clusters; calyx with pointed teeth, its tube adhering to the ovaries by means of a thickish, five-lobed disk; corolla bell-shaped, five-lobed, with five, small, triangular appendages, inside the tube, opposite the lobes; stamens with short, broad filaments and arrow-shaped anthers, slightly adhering to the blunt, obscurely two-lobed stigma; pod slender, cylindrical; seeds numerous, small, feathery.