Thelypteridaceae

Small to medium-sized deciduous ferns arising in a row and forming upright patches from a slender cord-like underground stem (rhizome); soft thin leaves that have a scattering of transparent needle-shaped hairs on the leaf and stem and wilt rapidly if picked; and small round spore-producing structures (sporangia) on the underside of the leaflets, nearly at the centre of the leaflet segments; Bog Fern, Marsh Fern and New York Fern.

Spore-producing structures are covered by a delicate horseshoe- or kidney-shaped membrane (indusium) that is attached at the deepest point of indentation (sinus). Leaves twice-divided, usually lack scales, margins of leaflet segments rounded. Fertile leaves arise later in the season that sterile ones. Leaf veins free, simple or forking, extending to the margins of the leaf segments. The upper part of the stem has a groove on its upper side.