class Monocotyledonae n : comprising seed plants that produce an embryo with a single cotyledon and parallel-veined leaves: includes grasses and lilies and palms and orchids; divided into four subclasses or superorders: Alismatidae; Arecidae; Commelinidae; and Liliidae [syn: {Monocotyledones}, {class Monocotyledones}, {Monocotyledonae}, {Liliopsida}, {class Liliopsida}]