Cystopteris fragilis is a small fern, with fronds to 40 cm long, but often about half that size. In some earlier treatments Cystopteris fragilis was interpreted in a broader sense to include C. laurentiana, C. tennesseensis, C. protrusas and C. tenuis as varieties. See steps 60-64 in the key to distinguish the species, or refer to the Flora of North America, vol. 2 for a more thorough treatment of this difficult group of species.

Cystopteris fragilis is broadly distributed across northern North America, south to California, New Mexico, northern Illinois, New York and Connecticut. In Wisconsin it is known from scattered locations, with the greatest incidence in Door County and near Lake Superior. It prefers rocks as a substrate.