Based on recent cladistic evidence, Cystopteridaceae should be construed as a separate family due to its basal position, sister to all other polypodioid ferns. This clade includes only the genera Acystopteris, Cystopteris

Cystopteris

Cystopteris is a genus of ferns. These are known generally as bladderferns or fragile ferns. They are found in temperate areas worldwide. This is a very diverse genus and within a species individuals can look quite different, especially in harsh environments where they experience stress and remain...

and Gymnocarpium

Gymnocarpium

Gymnocarpium is a small genus of ferns once placed with various other groups, including the dryopteroid ferns and the athyrioid ferns. Cladistic analysis has demonstrated that Gymnocarpium and Cystopteris form a natural but relatively primitive clade that is basal to the asplenoid, thelypterioid,...

. Woodsia

Woodsia

Woodsia is a genus of ferns in the family Woodsiaceae. It includes the following species :*Woodsia alpina S. F. Gray*Woodsia appalachiana T. M. C. Taylor*Woodsia cochisensis Windham...

is a more advanced species.

The ferns in this family generally have thin laminae, and small, round, naked sori

Sorus

A sorus is a cluster of sporangia .In fungi and lichens, the sorus is surrounded by an external layer. In some red algae it may take the form of a depression into the thallus....

.