One of the two classes which collectively make up the division Magnoliophyta (Angiospermae), the flowering plants. The Liliopsida, often known as Monocotyledoneae, or monocotyledons, embrace 5 subclasses (Alismatidae, Commelinidae, Arecidae, Zingiberidae, and Liliidae), 18 orders, 61 families, and about 55,000 species.