Osmundaceae is the only fern family of the order Osmundales; an order in the class Polypodiopsida 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.
Ferns of this family form heavy rootstocks with thick mats of wiry roots. Many species form short trunks; in the case of the genus Todea, they are sometimes considered as tree ferns because of the trunk, although it is relatively short.
Recent research on this family has significantly changed our understanding of the relationships of its species. The most striking finding is that O. cinnamomeum, despite its apparent similarity to Osmunda claytoniana, is actually the most anciently-derived species of the family, and so is a sister clade to the clade that comprises Osmunda, Todea, and Leptopteris (Jud et al. 2008), (Metzgar et al. 2008).