AMBROSIA: A genus of the pentandria order, belonging to the monœcia class of plants; and, in the natural method, ranking under the 49th order, Compositæ-nucamentaceæ. The characters are:—The MALE flowers are compound: The common calyx is a single-leaf'd perianthium, the length of the florets: The compound corolla is uniform, tubular, flat, and hemispherical; the proper is monopetalous, funnel-shaped, and quinquefid: The stamina consist of five very small filaments: the antheræ are erect, parallel, and pointed: The pistillum has a filiform style, the length of the stamina; the stigma orbicular and membranous: The receptaculum is naked.—FEMALE flowers below the male ones, on the same plant, doubled: The calyx is a single-leaf'd perianthium, entire (with the belly quinque-dentated), one-flowered, and persistent: There is no corolla: The pistillum has an ovate germen in the bottom of the calyx; a filiform style, the length of the calyx; and two long bristly stigmata: The pericarpium is an ovate unilocular nut: The seed is single and roundish. Of this genus five species are enumerated; but having no properties worthy of notice, we omit any farther account of them.