Rhizome tufted or creeping. Fronds tufted or scattered, 1- to 4-pinnate, delicate in texture; veins pinnate or forked, ultimate venules free. Sori dorsal, globose on the free venules. Indusium membranous, convex, attached to the venule below the sorus. There are five species from temperate regions. The name is from 7 Cystopteris 499 a bladder, and 7 Cystopteris 500 a fern, referring to the form of the indusium or involucre.

1. C. fragilis. Common Bladder Fern. - A handsome tufted Fern from 6 to 12 inches high, with bright green pinnate or bipinnate fronds on short brittle stipes. Pinnules triangular or ovate; rachis slightly winged. Sori few or many on each pinnule. Throughout Britain, though rare in the south, and widely spread in both the north and south temperate regions. C. dentata and C. Dickieana are varieties of this species.

C. montana is a delicate mountain species with 3- or 4-pinnate fronds, found at a great elevation in Scotland.

Orioclea sensibilis is a hardy North American Fern with separate barren and fertile fronds. The former are about 18 inches high, simply pinnate, with long lanceolate toothed pinnae, and the shorter fertile ones are bipinnate. Indusium inferior, bursting irregularly.

Struthiopteris Germanica is an allied Fern having the fronds disposed in a tufted rosette. The barren fronds are from 2 to 3 feet high, lanceolate, bipinnate with narrow pinnules. The fertile fronds are pinnate, and appear within the barren ones, and are much shorter. A widely diffused plant. Both this and the last are very handsome and desirable for planting in damp places, on the margins of pools, or partially in water.