Fern, green, nonflowering plant of the class Filicineae having creeping or erect rhizomes (rootstocks) or an erect aerial stem and large conspicuous leaves. Ferns may have appeared on earth more than 350 million years ago. The fern as it is commonly recognized is in its asexual sporophyte stage. Spores are produced on the underside of the leaf and germinate to form the sexual gametophyte stage of the life cycle. Ferns are widely distributed throughout the world and range in height from 1 in (2.5 cm) to 65 ft (20 m).