SMITHIA, in botany: A genus of the decandria order, belonging to the diadelphia class of plants; and in the natural method ranking under the 32d order, Papilionaceæ. The calyx is monophyllous and belabiated; the corolla winged; the legumen inclosed in the calyx, with three or four joints, and contain as many seeds, which are smooth, compressed, and kidney-shaped. There is only one species, viz. the thunna.