Plants perennial, terrestrial, on rock, or often epiphytic, erect, arching, or occasionally pendent. Stems long- to short-creeping, branched or not, bearing scales and few to numerous roots, usually dictyostelic. Leaves monomorphic to dimorphic, circinate in bud. Petiole usually articulate at base [rarely nonarticulate, as in Loxogramme ], lacking scales or sometimes scaly, with usually 3 vascular bundles. Blade petiole, rachis, costae, and sometimes blade tissue usually bearing hairs (these often septate and with reddish crosswalls) and/or scales. Sori borne abaxially on veins, round to oblong, occasionally elongate, rarely marginal, rarely covering surface; paraphyses present or absent; sporangia with stalk of 2 or 3 rows of cells; indusia absent. Spores usually transparent or yellowish (rarely greenish), all 1 kind, bilateral, monolete [rarely trilete, as in some Loxogramme], surface most often smooth, tuberculate, verrucose, or granulate, occasionally spiny, 64 per sporangium (spores globose and 32 per sporangium in apogamous spp.). Gametophytes green, aboveground, cordate or elliptic, glabrous or sometimes glandular; archegonia and antheridia borne on lower surface, antheridia 3-celled.

Genera ca. 40, species perhaps 500 (7 genera, 25 species in the flora): worldwide, especially tropics and subtropics.

Phymatosorus scolopendria (Burman f.) Pichi-Sermolli, native to the Old World, is a rare escape in southern Florida. Genera in this family are variously circumscribed, and the New World species historically were placed in the single genus Polypodium . Many of the segregates recognized here are still placed in Polypodium in recent floristic accounts. Limits of genera in both Old World and New World are controversial and are currently under study by several workers.

(Key to genera of Polypodiaceae)

Plants perennial, mostly small, on rock or commonly epiphytic [rarely terrestrial]. Stems long- to short-creeping or suberect, usually unbranched, bearing scales [rarely scales absent], solenostelic (having phloem on both sides of xylem) to dictyostelic (having complex nets of xylem). Leaves erect, arching, or pendent, monomorphic [rarely with specialized fertile areas], less than 50 cm [rarely longer], usually scaleless throughout. Petioles often dark-colored and wiry, commonly terete, usually less than 2 mm diam., articulate or not articulate, with 1 or 2 vascular strands. Blades simple and entire to commonly pinnatifid or 1-pinnate, rarely 2-pinnate or more divided, glabrous or commonly bearing hairs, especially on petioles and rachises; hairs tan to dark reddish brown [or transparent], unicellular to multicellular; rachises often dark-colored, not grooved adaxially. Veins free [to anastomosing in simple patterns]; hydathodes present or absent, sometimes obscured by lime dots adaxially. Sori abaxial on veins, round to oblong [occasionally elongate]; paraphyses present or absent, these glandular or hairlike; sporangia with stalk of 1 row of cells; indusia absent. Spores greenish, tetrahedral-globose, trilete, surface commonly papillate. Gametophytes greenish, borne aboveground, ribbon-shaped, sometimes bearing multicellular gemmae. Circumscription of genera is unsettled and in some cases arbitrarily based on blade dissection. Generic limits need redefinition and are the subject of current study. The family description above encompasses the worldwide variation. Relationships of the family have generally been thought to be with the Polypodiaceae with which the family is sometimes combined, but that is open to question. Most species are epiphytic, and many occur in cloud forests at middle and high elevations.