Caryopsis

Caryopsis (from the Greek caruon, a nut; opsis, resemblance) is the characteristic fruit of the grasses. It is composed of two, or more rarely, of three, carpels united into a one-chambered superior ovary containing one seed, which so completely fills it that the coats of the seed are adherent to the walls of the ovary. The whole of the grain, or small dry fruit, is often miscalled a "seed." It differs from the achene (q.v.) in being syncarpous, and from the cypsela (q.v.) and nut (q.v.) in being superior. The deep groove, frequent down one side of the caryopsis, marks the union of the two carpels. Nardus, and some other grasses, are exceptional, in having a monocarpellary fruit, which is consequently an achene.