Thelypteridaceae is a family of about 900 species of ferns.
These ferns typically have creeping rhizomes. The fronds are simply pinnate to pinnate-pinnatifid. There is either no frond dimorphism or only mild dimorphism, either open venation or very simple anastomosing. The sori are mostly reniform in shape and have indusia, except for the Phegopteris group.
Some researchers include the entire family Thelypteridaceae in the genus Thelypteris; others divide the family into as many as 30 genera. An intermediate position is to place the bulk in Thelypteris (which can then be divided into subgenera and sections corresponding to the genera of other authors) but to separate out Phegopteris and Macrothelypteris. Another choice is to divide the family into a half a dozen or so genera.
This family includes several complexes of species that are difficult to distinguish, and seem to represent a remarkable evolutionary radiation.
Recent genetic evidence shows that the family is clearly monophyletic. The same genetic studies show that the traditional genus Phegopteris is, in fact, a clearly segregate group that diverges at the very base of the family tree. In fact, this particular clade also includes the genera Pseudophegopteris and Macrothelypteris, which are here included in the larger genus Phegopteris. Similarly, Coryphopteris is included here in the genus Metathelypteris, Parathelypteris is included in Amauropelta, and a large group of genera are included in Cyclosorus.