Cystopteris fragilis is a species of fern known by the common names brittle bladder-fern and common fragile fern. It can be found worldwide, generally in shady, moist areas. The leaves are up to 30 or 40 centimeters long and are borne on fleshy petioles. Each leaf is divided into many pairs of leaflets, each of which is subdivided into lobed segments. The underside of the leaf has many rounded sori containing the sporangia.