Dryopteris expansa is a medium to large fern with blades up to 90 cm long and 30 cm wide. The blades are 3-pinnate-pinnatifid (at least at the base), slightly broader above the base and the basal pinnules are longer than the adjacent pinnules. The lower (basioscopic) basal pinnule is much longer than the upper (acroscopic) basal pinnule, often 2-3 times as long.

D. expansa is found in the east across Newfoundland, Quebec and Ontario, exending into northern Minnesota, Wisconsin and Michigan. It is also found in the extreme western states, north through western Canada to Alaska. It is listed as a "special concern" species in Wisconsin where it is restricted to the northern counties.