POLYPODIACEAE

one of several families in the fern order Polypodiales. The family contains 30 to 50 genera (depending on the authority consulted) and more than 1,000 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, 75 species), Platycerium (staghorn ferns , 17 species), Pleopeltis (40 species), Loxogramme (40 species), Microsorium (60 species), and Pyrrosia (100 species). The dwarf polypodies (Grammitis, about 150 species; Ctenopteris, about 200 species; and 7 other genera) are sometimes included in the family Polypodiaceae, but recent opinion favours their separation into a closely related family, Grammitidaceae. 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.