The Osmundaceae (Royal Fern Family) is a family of four genera and 15-25 species. It is the only fern family of the order Osmundales an order in the class Polypodiopsida (Filicopsida, Pteridopsida, or Leptosporangiate 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 Osmunda and Osmundastrum. In these genera the sporangia are borne naked on non-laminar pinnules, while Todea and Leptopteris bear sporangia naked on laminar pinnules. Ferns in this family are larger than most other ferns.