Osmundaceae (royal fern family) is a family of ferns containing four to six extant genera and 18–25 known species. It is the only living family of the order Osmundales in the class Polypodiopsida (ferns) or in some classifications the only order in the class Osmundopsida. This is an ancient (known from the Upper Permian) and fairly isolated group that is often known as the "flowering ferns" because of the striking aspect of the ripe sporangia in Claytosmunda, Osmunda, Osmundastrum, and Plensium (subtribe Osmundinae). In these genera the sporangia are borne naked on non-laminar pinnules, while Todea and Leptopteris (subtribe Todinae) bear sporangia naked on laminar pinnules. Ferns in this family are larger than most other ferns.