A class comprising seed plants that produce an embryo with a single cotyledon and parallel-veined leaves. It includes the grasses; lilies; palms; and orchids. It is divided into four subclasses or superorders: Alismatidae; Arecidae; Commelinidae; and Liliidae.

Liliopsida is the botanical name for a class. Publication of the name is credited to Scopoli (in 1760): see author citation (botany). This name is formed by replacing the termination -aceae in the name Liliaceae by the termination -opsida (Art 16 of the ICBN).