A rather large family, widely distributed, most abundant in America. Ours are herbs, often succulent, with no stipules; stems often fragile, swollen at the joints; leaves opposite, usually toothless, often unequal; flowers perfect, with no petals, but the calyx colored like a corolla, with four or five lobes or teeth, and more or less funnel-shaped; one or several flowers in a cluster with an involucre; stamens three to five, with slender filaments; style one, with a round-top stigma; the green base of the calyx drawn down around the ovary, making it appear inferior, and hardening into a nutlike fruit; seeds sometimes winged.

Quamoclidions have the odd habit of opening in the afternoon, hence the common name, Four-o'clock. The flowers usually have five stamens, and are grouped several together in a cluster, which emerges from an involucre so much resembling a calyx that it is often mistaken for one. The effect is of the flowers having clubbed together and made one calyx do for the lot. The fruit is hard, smooth, and roundish.