A subclass of the class Magnoliopsida (dicotyledons) in the division Magnoliophyta (Angiospermae), the flowering plants. The subclass consists of 8 orders, 39 families, and more than 12,000 species. The Magnoliidae are the most primitive subclass of flowering plants, being essentially coextensive with what has often been called the Ranalian complex. In general, they have a well-developed perianth, which may or may not be numerous, centripetal stamens, and they are apocarpous. Their ovules are bitegmic and crassinucellate, and their seeds usually have a small embryo and copious endosperm. All of these characters are subject to exception, however, and there is no one character or easy set of characters by which the group can be formally defined.

Various other putatively primitive characters, such as vesselless xylem, laminar stamens, laminar placentation, and the presence of more than two cotyledons, are largely or wholly restricted to this subclass, but are not standard features.