Cystopteris species

Bladder Ferns

Fragile Fern, Photo copyright by Earl J.S. Rook
Fragile Fern
Photo © by Earl J.S. Rook

Flora, fauna, earth, and sky...
The natural history of the northwoods


  • Cystopteris, from the Greek, kustis (cystis), "bladder" and pteris (pteris), "fern", a reference to the inflated indusia of these ferns.
  • Common name from the Greek botanical name
  • Other common names include Brittle Ferns


  • Kingdom Plantae, the Plants
    • Division Polypodiophyta, the True Ferns
      • Class Filicopsida
        • Order Polypodiales
          • Family Dryopteridaceae, the Wood Ferns
            • Genus Cystopteris, the Bladder Ferns
  • Taxonomic Serial Number: 17480
  • North Country species
  • About 20 species worldwide; 9 in North America.
  • A taxonomically difficult genus at the species level, especially the worldwide and polymorphic Cystopteris fragilis.


  • A genus of delicate, deciduous ferns of rocky woods.
  • Fronds monomorphic and deciduous
    • Petiole (leaf stalk) 1/3-3 times length of blade, base often swollen and persisting over winter.
    • Blade ovate-lanceolate to deltate, once to thrice cut, gradually reduced to a lobed tip.
    • Pinnae (primary leaflets) not articulate to axis; lowest pinnae not reduced.
  • Rootstalk creeping and scaly; stolons absent.
  • Sori round, in single row between midrib and margin on ultimate segments.
    • Indusia ovate to lanceolate, hoodlike and arching over sorus toward margin; often obscure at maturity.


  • Identifiable as Bladder Fern, not by bladders (That would be too easy, now wouldn't it?) but by thrice-cut, lacy fronds which are widest, or at least no more than semi-tapered, at the base.
  • Distinguished from one another with great difficulty.
    • Where Cystopteris species occur together, hybridization is likely.
    • Considerable overlap exists among frond shapes in Cystopteris species.
  • Field Marks
    • presence of bulblets
    • presence of hairs
    • shape of frond

Cystopteris ID for the North Country

    1. Check the suspected Cystopteris for hairs on the leaf stem and midrib. Check also for bulblets. The two characteristics go hand-in-hand. Bulblet bearing plants are hairy; hairy plants can bear bulblets though they are not always present. Confirm by looking at the overall shape of the frond. Hairy plants should have fronds which are widest at or near the base.
    2. If your specimen is hairy, with fronds widest at or near the base, you have either Bulblet Fern, Cystopteris bulbifera, or St. Lawrence Bladder Fern, Cystopteris laurentiana. Look at the hairs.
      • If the frond axis and leaflet ribs are densely covered with hairs, you most likely have Cystopteris bulbifera, Bulblet Fern. It will frequently bear bulblets and all but the earliest fronds of the season will bear sori; the young petioles will be reddish.
      • If the frond axis and leaflet ribs are only sparsely covered with hairs, you most likely have Cystopteris laurentiana, St. Lawrence Bladder Fern. It will occasionally bear bulblets (often misshapen) and nearly all leaves will bear sori; petioles will be dark brown to straw-colored or green. In our area, only recorded in Lake and Cook counties.
    3. If your specimen is neither hairy nor bulblet-bearing, with fronds widest at or just below the middle of the blade, look closely at the pinnae (leaflets).
      • If the pinnae are more or less perpendicular to the axis, and not curving toward blade tip, you have Cystopteris fragilis, Fragile Fern, our most common species. Leaflet edges will have sharp teeth.
      • If the pinnae are at an acute angle (less than 90°) to axis, and often curving toward the blade tip, you have Cystopteris tenuis, Upland Brittle Bladder Fern. Leaflet edges will be crinkled or have rounded teeth.
    4. If your specimen falls somewhere in between, remember that Cystopteris hybridizes readily, the hybrids only definitively identified by their shriveled and malformed spores.








  • By spore and vegetatively by rhizome


  • By rhizome division


  • Hardy to USDA Zone 3 (average minimum annual temperature -40ºF)
  • Some species available by mail order from specialty suppliers.



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Last Updated on 26 February, 2004