# Cystopteris
**Cystopteris** Bernh. is a genus of ferns known commonly as bladder ferns or brittle ferns, named for the bladder-like indusium, the membrane that covers the developing spore clusters. The name combines the Greek *kystos*, bladder, and *pteris*, fern, alluding to the indusium, which is inflated when young.[1](https://efloras.org/florataxon.aspx?flora_id=1&taxon_id=109134) The genus was first published in 1806 by the German botanist George Bernhardi in *Neues Journal für die Botanik*, and its native range is cosmopolitan, spanning temperate and cool habitats on every continent except [Antarctica](https://www.edgepedia.org/antarctica).[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A331105-2) • [3](https://sites.duke.edu/pryerlab/files/2017/12/cystopteridaceae_plastid_phylogeny.original.pdf)
| Key fact | Detail |
|---|---|
| Scientific name | *Cystopteris* Bernh., first published in Neues J. Bot. 1(2): 5, 26 (1806)[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A331105-2) |
| Common names | Bladder fern, bladderfern, brittle fern[1](https://efloras.org/florataxon.aspx?flora_id=1&taxon_id=109134) • [4](https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=17480) |
| Species count | 26 accepted species per Plants of the World Online; Flora of North America treats the genus as about 20 species worldwide, with 9 in North America[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A331105-2) • [1](https://efloras.org/florataxon.aspx?flora_id=1&taxon_id=109134) |
| Distribution | Cosmopolitan native range; introduced into the Chatham Islands[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A331105-2) |
| Ploidy pattern | Temperate species occur at tetraploid to octoploid ploidy levels; extant diploid species are concentrated in North America[1](https://efloras.org/florataxon.aspx?flora_id=1&taxon_id=109134) |
| Closest relatives | Sister genus *Acystopteris*; the two together are sister to *Gymnocarpium*[3](https://sites.duke.edu/pryerlab/files/2017/12/cystopteridaceae_plastid_phylogeny.original.pdf) |
| Evolutionary age | The family Cystopteridaceae last shared a common ancestor with other extant fern lineages approximately 100 million years ago[3](https://sites.duke.edu/pryerlab/files/2017/12/cystopteridaceae_plastid_phylogeny.original.pdf) |
## Description and name
Bladder ferns are small to medium rock- and forest-dwelling ferns of temperate climates. The generic name refers to the shape of the indusia, the thin membranes covering the sori, which resemble bladders.[1](https://efloras.org/florataxon.aspx?flora_id=1&taxon_id=109134) • [5](https://www.cuke.com/pdf-2015/tass-flora-VOL%20ONE%203%2031%202022.pdf) The fronds are delicate and brittle, a trait reflected in the common name brittle fern and in the specific epithet of the type species, *Cystopteris fragilis*, the fragile fern.[4](https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=17480)
## Classification
The family placement of *Cystopteris* has shifted with molecular evidence. Molecular phylogenies showed that *Cystopteris*, *Gymnocarpium*, and *Acystopteris* form a lineage distinct from both the dryopteroid ferns ([Dryopteridaceae](https://www.edgepedia.org/dryopteridaceae)) and the athyrioid ferns ([Athyriaceae](https://www.edgepedia.org/athyriaceae)), leading to the resurrection of the family Cystopteridaceae for these three genera.[3](https://sites.duke.edu/pryerlab/files/2017/12/cystopteridaceae_plastid_phylogeny.original.pdf) The Integrated Taxonomic Information System follows this placement, listing *Cystopteris* in Cystopteridaceae within the order [Polypodiales](https://www.edgepedia.org/polypodiales).[4](https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=17480) Plants of the World Online, by contrast, currently places the genus in Aspleniaceae.[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A331105-2)
Within the family, a plastid phylogeny covering most recognized species found all three sampled genera robustly monophyletic, with *Cystopteris* strongly supported as sister to *Acystopteris* and the pair together sister to *Gymnocarpium*.[3](https://sites.duke.edu/pryerlab/files/2017/12/cystopteridaceae_plastid_phylogeny.original.pdf) The genus itself contains four deeply diverged lineages: the *C. montana* clade, the *sudetica* clade, the *bulbifera* clade, and the *C. fragilis* complex, with *C. montana* sister to the rest of the genus.[3](https://sites.duke.edu/pryerlab/files/2017/12/cystopteridaceae_plastid_phylogeny.original.pdf) • [6](https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.14111)
The genus has absorbed former segregates. The monotypic Chinese genus *Cystoathyrium*, known from a single species in western Sichuan, was reported to be nested within *Cystopteris* as sister to the North American *C. bulbifera* clade with strong support, and *Cystoathyrium* is now listed as a heterotypic synonym of *Cystopteris*.[7](https://onlinelibrary.wiley.com/doi/10.1111/jse.12141) • [2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A331105-2) Other synonyms include *Cyclopteris* Gray, *Cystea* Sm., *Filicula* Ség., *Filix* Adans., and *Rhizomatopteris* A.P.Khokhr.[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A331105-2)
## Hybridization and the C. fragilis complex
Past and present hybridization makes the genus difficult to identify, and species boundaries within it remain actively studied.[8](https://gobotany.nativeplanttrust.org/dkey/cystopteris/) Hybridization and allopolyploidy involving *Cystopteris bulbifera*, the bulblet fern, and other North American species have generated several species; *C. bulbifera* may hybridize with *C. tenuis* to form *C. × illinoensis*.[9](https://efloras.org/florataxon.aspx?flora_id=1&taxon_id=200003866) Hybrids between *C. bulbifera* and members of the *C. fragilis* sensu lato clade include *C. laurentiana*, and the oldest species name for that group of hybrid taxa is *C. tennesseensis*.[10](https://sites.duke.edu/pryerlab/files/2022/07/WindhamPryer.JBRIT_.2022.Cystopteris.pdf)
The *C. fragilis* complex is the largest challenge in the genus. Cytogenetic, geographic, spore-type, and plastid haplotype data have revealed cryptic patterns of species diversity within this cosmopolitan group, which includes species such as *C. alpina*, *C. diaphana*, *C. douglasii*, *C. tasmanica*, and *C. tenuis* alongside *C. fragilis* itself.[11](https://academic.oup.com/botlinnean/article/199/3/728/6510911) A nuclear phylogeny of the family confirmed that rampant allopolyploidy has shaped its evolution.[7](https://onlinelibrary.wiley.com/doi/10.1111/jse.12141)
## Distribution and ecology
The genus is native on every continent except Antarctica, occurring from the Arctic to southern South America and from oceanic islands such as Hawai'i, the [Kerguelen Islands](https://www.edgepedia.org/kerguelen-islands), and [South Georgia](https://www.edgepedia.org/south-georgia) to continental interiors across Eurasia, Africa, and the Americas.[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A331105-2) • [3](https://sites.duke.edu/pryerlab/files/2017/12/cystopteridaceae_plastid_phylogeny.original.pdf) *Cystopteris fragilis* sensu lato is perhaps the most widely distributed fern in the world, ranging from the high arctic to [Tierra del Fuego](https://www.edgepedia.org/tierra-del-fuego) in the Americas, blanketing most of Eurasia, and occurring in eastern and southern Africa, eastern Australia, New Zealand, Hawai'i, and many isolated rocky oceanic islands.[3](https://sites.duke.edu/pryerlab/files/2017/12/cystopteridaceae_plastid_phylogeny.original.pdf)
Species grow mainly in temperate climates, often in rocky habitats, and the family is ubiquitous in rocky habitats across the northern hemisphere.[1](https://efloras.org/florataxon.aspx?flora_id=1&taxon_id=109134) • [3](https://sites.duke.edu/pryerlab/files/2017/12/cystopteridaceae_plastid_phylogeny.original.pdf) Fossil spores of *Cystopteris dickieana* type were present in Britain in the Late Weichselian, about 15,000 radiocarbon years before present, indicating a long post-glacial history in the region.[12](https://besjournals.onlinelibrary.wiley.com/doi/10.1111/j.1365-2745.2012.01985.x)
## Notable species
- *Cystopteris bulbifera* (L.) Bernh., the bulblet fern, reproduces also by bulbils on the frond and is a diploid parent of several hybrid species.[9](https://efloras.org/florataxon.aspx?flora_id=1&taxon_id=200003866) • [13](https://wcbotanicalclub.org/wp-content/uploads/2016/05/weakleyflora_2012-sep-noimages-part1_13-125.pdf)
- *Cystopteris fragilis* (L.) Bernh., the fragile fern, the type species of the genus and center of the largest species complex.[4](https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=17480) • [11](https://academic.oup.com/botlinnean/article/199/3/728/6510911)
- *Cystopteris montana* (Lam.) Bernh. ex Desv., the mountain bladder fern, sister to the rest of the genus and distributed across temperate Eurasia and North America.[3](https://sites.duke.edu/pryerlab/files/2017/12/cystopteridaceae_plastid_phylogeny.original.pdf) • [14](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A17076650-1)
- *Cystopteris protrusa* (Weath.) Blasdell, the lowland bladder fern, sister to the rest of the *C. fragilis* complex.[6](https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.14111)
## References
1. [Cystopteris, Flora of North America, efloras.org](https://efloras.org/florataxon.aspx?flora_id=1&taxon_id=109134)
2. [Cystopteris Bernh., Plants of the World Online, Royal Botanic Gardens, Kew](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A331105-2)
3. [Rothfels, C. J., Windham, M. D., & Pryer, K. M. (2013). A Plastid Phylogeny of the Cosmopolitan Fern Family Cystopteridaceae (Polypodiopsida). Systematic Botany 38(2): 295–306](https://sites.duke.edu/pryerlab/files/2017/12/cystopteridaceae_plastid_phylogeny.original.pdf)
4. [Cystopteris, Integrated Taxonomic Information System (TSN 17480)](https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=17480)
5. [Tassajara Flora, Pteridophyta: Cystopteridaceae to Dennstaedtiaceae](https://www.cuke.com/pdf-2015/tass-flora-VOL%20ONE%203%2031%202022.pdf)
6. [Rothfels, C. J. (2017). Next-generation polyploid phylogenetics: rapid resolution of hybrid polyploid complexes using PacBio single-molecule sequencing. New Phytologist](https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.14111)
7. [Xiang, L. et al. (2015). Evolution of the eastern Asian–North American biogeographic disjunctions in ferns and lycophytes. Journal of Systematics and Evolution](https://onlinelibrary.wiley.com/doi/10.1111/jse.12141)
8. [Cystopteris: Dichotomous Key, Go Botany, Native Plant Trust](https://gobotany.nativeplanttrust.org/dkey/cystopteris/)
9. [Cystopteris bulbifera, Flora of North America, efloras.org](https://efloras.org/florataxon.aspx?flora_id=1&taxon_id=200003866)
10. [Windham, M. D. & Pryer, K. M. (2022). New nomenclatural combinations in Cystopteris. Journal of the Botanical Research Institute of Texas](https://sites.duke.edu/pryerlab/files/2022/07/WindhamPryer.JBRIT_.2022.Cystopteris.pdf)
11. [Cytogenetic, geographical, spore type and plastid haplotype data reveal cryptic patterns of species diversity in the cosmopolitan Cystopteris fragilis complex. Botanical Journal of the Linnean Society 199(3): 728](https://academic.oup.com/botlinnean/article/199/3/728/6510911)
12. [Rünk, S. et al. (2012). Biological Flora of the British Isles: Dryopteris carthusiana, D. dilatata and D. expansa. Journal of Ecology](https://besjournals.onlinelibrary.wiley.com/doi/10.1111/j.1365-2745.2012.01985.x)
13. [Weakley, A. S. (2012). Flora of the Southern and Mid-Atlantic States](https://wcbotanicalclub.org/wp-content/uploads/2016/05/weakleyflora_2012-sep-noimages-part1_13-125.pdf)
14. [Cystopteris montana (Lam.) Bernh. ex Desv., Plants of the World Online, Kew](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A17076650-1)
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*Topic: Encyclopedia › Life and health › Plants and algae › Ferns and lycophytes › Other leptosporangiate fern families › Wood and shield ferns (Dryopteridaceae) › Cystopteris, Gymnocarpium, and bladder/chain-fern allies*
*Initially written Sep 17, 2026 · Reviewed: Oct 21, 2026 · Edited: Oct 15, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*
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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license