·noun A genus of simple ascidians, which formerly included most of the known species. It is sometimes used as a name for the Ascidioidea, or for all the Tunicata.
II. Ascidium ·noun A pitcher-shaped, or flask-shaped, organ or appendage of a plant, as the leaves of the pitcher plant, or the little bladderlike traps of the bladderwort (Utricularia).