Extensive fossil record dating from the Devonian. Homosporous with exosporic bisexual gametophytes. Gametophytes are free living and either photosynthetic or subterranean and dependent on a fungus for nutrition. Sporangia are borne on sporophylls. Sporophylls are either grouped in terminal aggrgations to form a strobilus or are distributed in alternating clusters with non sporangium bearing leaves.
Some species reproduce vegetatively by means of bulbils.