Alpine Bladder-fern vs Coastal Silver-stiletto

Cystopteris alpina compared with Acrosathe annulata

Key Differences

Alpine Bladder-fern is Near Threatened while Coastal Silver-stiletto is Least Concern.

Taxonomic Classification

Rank	Alpine Bladder-fern	Coastal Silver-stiletto
Kingdom	Plantae (Plants)	Animalia (Animals)
Phylum	Tracheophyta	Arthropoda (Arthropods)
Class	Polypodiopsida (Polypodiopsida)	Insecta (Insects)
Order	Polypodiales (Polypodiales)	Diptera (Diptera)
Family	Cystopteridaceae	Therevidae
Genus	Cystopteris	Acrosathe
Species	Cystopteris alpina	Acrosathe annulata

Conservation Status

Alpine Bladder-fern

NT — Near Threatened

Coastal Silver-stiletto

LC — Least Concern

Physical Characteristics

Attribute	Alpine Bladder-fern	Coastal Silver-stiletto
Diet	—	—
Average Lifespan	—	—
Average Length	—	—
Average Weight	—	—

Habitat & Geographic Range

Alpine Bladder-fern

Habitat

Typically found in moist, shaded forest floors and tropical canopies.

Range

Distributed across Norway and Sweden. Listed as Near Threatened, this species requires ongoing monitoring to prevent population decline.

Coastal Silver-stiletto

Habitat

Typically found in virtually all terrestrial and freshwater habitats.

Range

Distributed across Belgium, Denmark, Norway, and Sweden.

Alpine Bladder-fern

The Alpine Bladder-fern (Cystopteris alpina) is a species in the genus Cystopteris. It is currently classified as Near Threatened on the IUCN Red List. Typically found in moist, shaded forest floors and tropical canopies. Distributed across Norway and Sweden. Listed as Near Threatened, this species requires ongoing monitoring to prevent population decline.

Coastal Silver-stiletto

Coastal silver stiletto (Acrosathe annulata) is a slender robber fly in the family Therevidae, native to northwestern Europe, including the United Kingdom, France, the Netherlands, Belgium, and Scandinavia. Adults are found on coastal sand dunes and sandy heathland, where they perch on bare sand to ambush small flying insects. Stiletto flies in the family Therevidae are characterised by a slender body, long pointed abdomen, and predatory habits; adults prey on a variety of small dipterans and other flying insects during warm, sunny periods. Larvae develop in sandy soil, where they are also predatory, feeding on other invertebrate larvae. Acrosathe annulata is a habitat specialist restricted to open, sandy coastal habitats with sparse vegetation—environments that have declined substantially across northwestern Europe due to dune stabilisation, recreational disturbance, and the cessation of traditional dune management. The IUCN lists it as Least Concern, though regional conservation bodies in the United Kingdom have flagged population declines. It is considered an indicator of high-quality coastal sand dune habitats and is monitored through national invertebrate surveys.