Perennial herbs with creeping rhizomes, bearing aerial stems at intervals. Stems all green or the fertile stems without chlorophyll, all grooved, simple or branched from near the base, with the branches resembling the stems or with whorls of slender green branches from the nodes, with a central cavity surrounded by two circles of smaller cavities, the larger, outer ones called vallecular canals. Leaves in whorls, united into sheaths above the nodes, the sheaths ending in free teeth usually of the same number as the grooves on the stem, usually not green; sheaths of branches much smaller with fewer teeth. Sporangiophores in whorls, closely aggregated to form a spike or cone, usually terminal on the main stem and occasionally also on the branches. Spores all alike, numerous in sporangia borne in groups around the under surface of the sporangiophore. Archegonia and antheridia borne on separate gametophytes, the female being larger. Gametophytes with a cushion-like base bearing green flat lobed structures arising from the under surface, with the sex organs borne on the upper surface of the cushion. Spermatozoids multiciliate.