Family Description: Rhizome dictyostelic, with clathrate scales. Petiole with 2 vascular strands, often fusing to form a single ×-shaped strand. Sori superficial, borne along one or both sides of the fertile veins; spores bilateral.
Family Description: Rhizomes subterranean, far-creeping. Stems grooved and regularly jointed. Leaves in whorls, united at the base into a sheath. Homosporous; cones composed of sporangiophores; sporangia borne beneath the peltate heads of the sporangiophores; spores spherical with 4 elaters, green. Prothallus green.
Family Description: Stem short, 2- or 3-lobed. Leaves in a rosette; leaf-base spathulate, with a membranous margin, with a delicate ligule on the adaxial surface at the point where the leaf narrows. Heterosporous; megaspores tetrahedral; microspores bilateral, in separate sporangia.
Family Description: Rhizome polystelic or solenostelic, with opaque scales. Leaves 2-ranked on the upper side of the rhizome and articulated to it; petiole with 1-3 major vascular strands. Sori superficial, without indusium; spores bilateral.
Family Description: Rhizome solenostelic or dictyostelic, with opaque scales. Petiole with a single U-shaped strand. Sori submarginal, forming coenosori which are borne on the veinlet connecting the vein ends, and which are covered by the scarious, deflexed leaf-margins; spores tetrahedral, opaque.
Family Description: Stems slender, branched, floating. Leaves in whorls of 3, very hairy; 2 of the leaves entire, floating, the third submerged. Heterosporous; sori at the base of the submerged leaves, stalked, surrounded by a thin-walled, hairy indusium, and consisting of either numerous microsporangia or a few megasporangia, or occasionally mixed.
Family Description: Stems erect or creeping. Leaves numerous, simple, small, 1-veined, with a ligule on the adaxial surface. Heterosporous; sporangia grouped in strobili; individual sporangia solitary at the base of the sporophylls, unilocular; spores tetrahedral.