Thelypteris palustris is a creeping, fern with a slender, pubescent rhizome. The leaves are upright, and can reach up to 1.2 m in length. The structure containing the sporangia is on the lower page of the leaf and presents irregularly dentate, glandular and deciduous appearance.

Occurs in wetlands, flooded areas, more or less dark places, such as lagoons banks, bogs, marsh willows, marshes and other wetland sites.