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Mostly perennial (always in Australia); primary stems erect, rooting at the base only and then usually spreading by creeping sobols, or creeping and semiprostrate, rooting in the axils of the branch dichotomies; branches often compound, often forming a pseudopinnate, complanate 'frond'-like arrangement on which the strobili form at the branch tips and mature simultaneously. Leaves dimorphic, at least on the secondary branches, in 4 distinct rows, those of the 2 upper (dorsal or median) rows being distinctly smaller than those on the lower (ventral) lateral rows; median leaves appressed and directed along the axis; lateral leaves in 1 plane, ±squarely inserted. Sporophylls uniform and tetrastichous.
Perennial rhizome creeping and much-branched, or secondary branches erect and shrubby, rooting at the branch axils. Leaves as in subg. Stachygynandrum. Strobili complanate; sporophylls dimorphic, arranged as in sterile leaves or resupinate with those on the ventral side smaller than those on the dorsal side of the shoot, with a wing-like structure on the adaxial side of the lamina partly covering the sporangium.
Annual plants, with a usually simple erect rhizome, or perennial with more compound erect stems, either solitary and arising from a fleshy underground solenostelic rhizome, or several and tufted from a compact aerial rootstock. Leaves monomorphic, decussate at least below, arranged in opposite pairs; each pair at right-angles to the pair on either side of it; sporophylls tetrastichous.
Plants mat-forming, creeping, erect, or pendent-epiphytic. Stems slender. Lvs numerous, c. 0.5-10 mm long, 1-veined, either all similar and spirally arranged, or dimorphic and 4-ranked with lower patent and upper appressed, pointing forwards. Strobili terminal, usually quadrangular, occasionally cylindric. Megasporangia basal, > apical microsporangia. Spores trilete.
Morphological characters and geographic distribution are the same as those of the family.
Terrestrial evergreen herbs superficially resembling mosses. 500, cosmop.
Description as for family.
