Polypodiidae is a subclass of Polypodiopsida (ferns), and of the four subclasses comprises the vast number of species. It is equivalent to the Polypodiopsida sensu stricto in the system of Smith et al. (2006).
The division of the ferns (Polypodiopsida) sensu lato into four major groups has been demonstrated using both molecular and morphological criteria. Smith et al. (2006) carried out the first higher-level pteridophyte classification published in the molecular phylogenetic era, and considered the ferns as monilophytes, with four classes, referring to this group as Polypodiopsida sensu stricto.
Later classifications renamed the group Polypodiidae, initially as a subclass of Equisetopsida sensu lato. This subclass comprises leptosporangiate ferns as opposed to the remaining three subclasses which are informally referred to as eusporangiate ferns.The following diagram shows a likely phylogenic relationship between subclass Polypodiidae and the other Equisetopsida subclasses in that system