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Cornish Bladder Fern

Cystopteris diaphana

Please keep in mind that it is illegal to uproot a plant without the landowner's consent and care should be taken at all times not to damage wild plants. Wild plants should never be picked for pleasure and some plants are protected by law.
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Plant Profile

Cystopteridaceae (Bladder Fern)
Life Cycle:
Maximum Size:
40 centimetres tall
Cliffs, meadows, mountains, riverbanks, riversides, rocky places, woodland.
Ferns reproduce using spores and therefore this species does not have any flowers.
Black spores with whitish cases.
2 to 3-pinnate leaves (fronds) with toothed leaflets. Similar in appearance to Brittle Bladder Fern (Cystopteris fragilis) but the leaf veins between the teeth end in notches. The leaves are evergreen therefore are present all year round. Very rare plant, first discovered in Cornwall in the year 2000.
Other Names:
Diaphanous Bladder-fern, Diaphanous Fern, Greenish Bladder Fern.
Frequency (UK):
Rarely seen  

Similar Species

Other Information


Cystopteris diaphana, also known as the diaphanous bladder fern, is a species of fern that is native to North America, Asia, and Europe. It is a small to medium-sized fern that typically grows in rocky crevices, on cliffs, and on ledges in damp, shady environments.

The fronds of C. diaphana are triangular in shape and are typically 15-30 cm long. They are deeply lobed, with the lobes being lanceolate in shape. The stipe (the stem of the frond) is typically red-brown in color, and the rachis (the axis of the frond) is typically green. The sori (clusters of spore-producing structures) are located on the undersides of the fronds, and are protected by reflexed marginal flaps.

C. diaphana is considered to be a common and widespread species, not considered globally threatened. It has a wide distribution range and can be found in a variety of habitats, from wet meadows and moist woods, to rocky cliffs, talus slopes and alpine habitats.

It is an ornamental fern that can be used in the same way as C. fragilis and C. dickieana, it can be grown in rock gardens, hanging baskets, and as a terrarium plant. It prefers to be in moist, shaded, or partially shaded areas, also tolerates well cold.

The plant has been traditionally used in medicine and food in some cultures, due to its high content of essential minerals and vitamins.


The Cornish Bladder Fern, also known as Cystopteris diaphana, is a small, delicate fern that is native to the UK and parts of Europe. It is named after its translucent, bladder-like sacs that contain spores, which can be seen when the fern is backlit.

The Cornish Bladder Fern is a relatively small plant, usually growing to no more than 30cm in height. Its fronds are pale green and finely divided, giving them a delicate, lacy appearance. They are arranged in a rosette, which makes the fern easy to identify.

Cystopteris diaphana is a versatile plant that can grow in a range of habitats, from rocky outcrops to woodland floors. It is particularly common in the south-west of the UK, where it is often found growing on damp, shaded rocks and cliffs. It is also found in parts of Europe, including Scandinavia, Germany, and the Pyrenees.

The Cornish Bladder Fern is an important plant for wildlife. Its fronds provide shelter and nesting sites for a range of insects and small animals. The plant is also an important food source for some species of moth, including the pretty Satin Wave and the Grass Emerald.

Despite its small size and delicate appearance, the Cornish Bladder Fern is a hardy plant that can tolerate a range of conditions. It is relatively easy to grow in gardens, and makes an attractive addition to rockeries, shady borders, and woodland gardens.

However, the Cornish Bladder Fern is also at risk in some areas. It is protected under UK law, and it is illegal to uproot or disturb the plant without a licence. This is because the fern is threatened by habitat loss and degradation, particularly in areas where it is found on rocks and cliffs that are popular with climbers and walkers.

The Cornish Bladder Fern is part of the Cystopteris genus, which includes around 16 species of ferns found around the world. The genus name comes from the Greek words "kystis", meaning bladder, and "pteris", meaning fern. The specific epithet "diaphana" comes from the Greek word for transparent, referring to the translucent nature of the fern's sacs.

Like all ferns, the Cornish Bladder Fern reproduces through spores rather than seeds. These spores are produced in the bladder-like sacs on the underside of the fronds. When the spores are mature, the sacs burst open, releasing the spores into the air. If conditions are right, the spores can then germinate and grow into new ferns.

The Cornish Bladder Fern has a long history of medicinal and culinary use. In the past, the fern was used to treat a range of ailments, including coughs, fevers, and stomach problems. It was also used in food, both as a vegetable and as a flavouring for drinks such as beer and mead. However, these uses are now largely obsolete, and the fern is primarily valued for its ornamental and ecological value.

If you're interested in growing the Cornish Bladder Fern in your garden, there are a few things to keep in mind. The fern prefers a damp, shady spot with well-drained soil. It can be grown from spores or by dividing an existing plant in the spring. Once established, the fern is relatively low maintenance, requiring only occasional watering and fertilizing.

The Cornish Bladder Fern is also sometimes called the "Brittle Bladder Fern" because its fronds are relatively thin and delicate. While the fern can tolerate a range of conditions, it is particularly sensitive to pollution and other environmental stresses. This makes it an important indicator species for monitoring the health of ecosystems where it is found.

In addition to its ecological importance, the Cornish Bladder Fern has cultural significance as well. It has been featured in art and literature throughout history, from ancient Celtic legends to modern paintings and poems. The fern is also an important symbol in Cornish culture, where it is often associated with the natural beauty of the county and its rugged coastline.

The conservation status of the Cornish Bladder Fern varies depending on its location. In the UK, the fern is classified as "Near Threatened" due to habitat loss and degradation, particularly in areas where it is found on rocks and cliffs that are popular with climbers and walkers. In other parts of Europe, the fern is more common and is not considered to be at risk.

Efforts are underway to protect the Cornish Bladder Fern and its habitat in the UK. This includes the creation of protected areas and the implementation of conservation measures to reduce disturbance to the fern and its surroundings. Education and outreach efforts are also important, as many people are unaware of the fern's existence and ecological importance.

In conclusion, the Cornish Bladder Fern is a small but significant plant with a rich history and important ecological role. Whether you're a conservationist, a gardener, or simply someone who appreciates the natural world, this delicate and versatile fern is well worth learning more about and protecting.