Cystopteris is a taxonomically difficult genus at the species level. Especially troublesome is the worldwide and polymorphic species Cystopteris fragilis sensu lato. To maintain it as a single species with several varieties (as is done here) would be easiest (and least controversial). This approach, however, may not accurately reflect true evolutionary history[].

Common Name: Brittle Bladder Fern

General Information

Cystopteris fragilis is a deciduous fern with creeping stems; it forms a slowly spreading clump usually around 15 - 25cm tall and 20cm or more wide.
The plant is sometimes harvested from the wild for local use as a medicine or an emergency food. It is grown as an ornamental, where it can be used as a ground cover in shady places.

Known Hazards

Although we have found no reports of toxicity for this species, a number of ferns contain carcinogens so some caution is advisable[].
Many ferns also contain thiaminase, an enzyme that robs the body of its vitamin B complex. In small quantities this enzyme will do no harm to people eating an adequate diet that is rich in vitamin B, though large quantities can cause severe health problems. The enzyme is destroyed by heat or thorough drying, so cooking the plant will remove the thiaminase[].

Botanical References

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Range

A cosmopolitan species, found in most areas of the world, including Britain, but only at higher elevations in Tropics.

Habitat

Mostly on cliff faces, also in thin soil over rock; at elevations from near sea level to 4,500 metres[]. Rocky woods, shady rocks and walls, especially on basic rocks, to 1,200 metres[].

Properties

Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Deciduous Fern
Height	0.15 m
Cultivation Status	Ornamental, Wild

Cultivation Details

Cystopteris fragilis is very widely spread through the temperate zone, can be found at elevations up to 4,500 metres. A very cold-tolerant plant, when fully dormant it can withstand temperatures down to below -30°c[].
Prefers a shady position in a moist but well-drained soil, succeeding in most soil types[]. Plants can tolerate up to 4 hours direct sun per day[]. Prefers a pH between 6.5 and 7, but tolerates a range from 5.5 to 7.5[]. Plants do especially well when grown in a shaded position on old mortared walls[].
Members of this genus are rarely if ever troubled by browsing deer[].
Plants die back early in dry seasons[].
A very ornamental plant[].

Edible Uses

Root. An emergency food, it is only used when all else fails[].

Medicinal

A decoction of the roots has been used as an anthelmintic enema[].

A cold compound infusion of the plant has been used both internally and externally as a treatment for injury[].

Agroforestry Uses:

Plants can be grown as a ground cover when planted out about 15cm apart each way[].

Other Uses

None known

Propagation

Spores - best sown as soon as ripe on the surface of a humus-rich sterilized soil. Keep the compost moist, preferably by putting a plastic bag over the pot. Germinates in 1 - 3 months at 20°c[].Pot on small clumps of plantlets as soon as they are large enough to handle and keep humid until they are well established. Do not plant outside until the ferns are at least 2 years old.
Division in spring.