Terrestrial, epilithic or epiphytic herbs, annual or perennial. Stems erect or creeping and mat forming, simple or dichotomously branched, glabrous or pubescent; roots arising basally or throughout the lenght of the stem, mainly from the branch axils. Leaves ligulate, thin, simple with an unbranched central vein,glabrous or hairy, either spirally arranged and ± similar in shape and size or dimorphic and 4-ranked, the lower (lateral leaves) patent, the upper (median leaves) appressed and pointing forwards. Sporangia dehiscent with 2 valves, borne singly in the axils of sporophylls arranged in cones.