in botany: A genus of the triandra digynia class; and, in the natural method, ranking under the 4th order, Gramina. The calyx has a double valve; the corolla has one valve, and three awns at the points. There are three species of arilidae, viz. the adscensionis, a native of the island of Ascension; the Americana, a native of Jamaica; and the plumosa, a native of America.