(δια, "twice," and ἄλυτος, "a brother"), the 17th class in the sexual system, comprehending those plants which bear hermaphrodite flowers with two sets of united stamens; but this circumstance must not be absolutely depended on. They are the papilionaceae of Tournefort, the irregulares tetrapetalii of Rivinus, and the leguminosae of Ray. See Botany Index.