Polypodiaceae, family (including Grammitidaceae) in the order Polypodiales, which contains 56 genera and about 1,200 species of diverse and widely distributed medium-sized and small ferns. Some earlier classification systems have recognized as many as 170 genera and 7,000 species in the family, most of which are now placed in other families. This entire larger group is still often referred to as polypodiaceous ferns, however, because all exhibit certain characteristics considered to be evolutionarily advanced—i.e., long-stalked, spore-producing structures (sporangia) characterized by the presence of an incomplete, vertically arranged band of thick-walled cells (annulus). In addition, members of the presently recognized family are mostly tropical and subtropical epiphytes (plants not rooted in soil but growing upon other plants) with a rootlike creeping stem (rhizome) covered with distinctive scales. The lower surfaces of the leaves bear round or oblong clusters of sporangia (sori) that usually lack the protective membranous covering (indusium) found in many other fern families. The genera are distinguished by numerous characteristics such as presence and type of plant hairs on stems and leaves, arrangement of sori, rhizome type, growth habit, and others. The limits of the family and many of its included genera are still in need of study.
Some of the chief genera include Polypodium (true polypodies, about 150 species), Platycerium (staghorn ferns, 17 species), Pleopeltis ( 15–50 species), Loxogramme ( 33 species), Microsorium (60 species), and Pyrrosia ( about 100 species). The genera Solanopteris (3 species) and Lecanopteris (3–4 species) are unusual in having swollen hollow stems inhabited by ants. The dwarf polypodies (Grammitis and its relatives from the former family Grammitidaceae, about 750 species) were included in Polypodiaceae following new DNA evidence.
Economically, the family is of little importance except for the few grown as ornamentals, the most popular of which are the staghorn ferns and true polypodies.