Fern, any of several nonflowering vascular plants that possess true roots, stems, and complex leaves and that reproduce by spores.
Ferns are extremely diverse in habitat, form, and reproductive methods. In size alone they range from minute filmy plants only 2 to 3 mm (0.08 to 0.12 inch) tall to huge tree ferns 10 to 25 metres (30 to 80 feet) in height. Some are twining vines; others float on the surface of ponds. The majority of ferns inhabit warm, damp areas of the Earth.