Cystopteris fragilis

Fragile Fern

Fragile Fern
Photo © Earl J.S. Rook

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

Name:

• Cystopteris, from the Greek, kustis (cystis), "bladder" and pteris (pteris), "fern", a reference to the inflated indusia of these ferns.
• fragilis, from the Latin, " easily broken, brittle, fragile"
• Common name from the specific epithet.
• Other common names include Brittle Fern, Bladder Fern, Brittle Bladder Fern, Northern Fragile Fern, Cystoptéris Fragile, Cystoptère Fragile (Qué), Brittle Bladder-fern, Dickie's Bladder-fern (UK), Stenbräken (Swe), Skjørlok, Berglok (Nor), Skør Bægerbregne (Dan), Haurasloikko (Fin), Tófugras (Is), Zerbrechlicher Blasenfarn, Dickie's Blasenfarn (Ger)

Taxonomy:

• 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: 17482
• Also known as Cystopteris dickieana, Filix fragilis, Polypodium fragile

Description:

• A small, bright green, deciduous fern of rocky places, growing as asymmetrical clump.
• Fronds monomorphic, 6"-12", nearly all bearing sori.
  • Petiole (leaf stalk) slender and smooth, dark brown/black at base, becoming yellow or green above; shorter than or nearly equaling blade; base sparsely scaly.
  • Blade lanceolate to narrowly elliptic, thrice-cut and lacy, widest at or just below middle, tip pointed. Rachis and leaf ribs lack hairs or bulblets.
  • Pinnae (primary leaflets) usually perpendicular to rachis, not curving toward blade apex, margins toothed.
  • Pinnules (secondary leaflets) highly variable in dissection; veins directed mostly into teeth.
• Rootstalk creeping, not cordlike, internodes short, beset with old petiole bases, hairs absent; scales tan to light brown, lanceolate.
  • Roots black and rather heavy; numerous.
• Sori on undersides of leaflets
  • Indusia ovate to lanceolate, without hairs.
  • Spores spiny.

Identification:

• Identifiable as a Bladder Fern by thrice-cut, lacy fronds and rocky habitat.
• WARNING: Cystopteris species are distinguished from one another with great difficulty and often not a little bit of frustration. The "distinguishing" characteristics are often difficult to identify clearly and there is a fair amount of overlap. That said:
  • Distinguished from Bulblet Fern, Cystopteris bulbifera, and St. Lawrence Bladder Fern, Cystopteris laurentiana by the absence of hairs and bulblets and by fronds widest at or just below the middle of the blade.
  • Distinguished from Upland Brittle Bladder Fern, Cystopteris tenuis, by having pinnae more-or-less perpendicular to the axis, and not curving toward blade tip.
• Field Marks
  • rocky habitat
  • thrice-cut lacy fronds
  • absence of tiny hairs on rachis and indusia
  • absence of bulblets

Distribution:

• Alaska to Newfoundland, south to California, Nevada, New Mexico, Texas, Iowa, Illinois, Indiana, Ohio, Pennsylvania, New York, and New England. Also Greenland.
• Worldwide

Habitat:

• Mostly on cliff faces; also damp rocks and walls and on thin soil over rock, avoiding the most acidic rocks.
• Occurs at higher latitudes and/or elevations than other species of Cystopteris.

Fire:

Associates:

• Herbs: Columbine (Aquilegia canadensis), Wild Sarsaparilla (Aralia nudicaulis), Rattlesnake Root (Prenanthes alba)
• Ferns: Bulblet Fern (Cystopteris bulbifera), Wood Ferns (Dryopteris spp.), Common Polypody (Polypodium virginianum)

History:

Uses:

Reproduction:

• By spore and vegetatively by rhizome

Propagation:

• By rhizome division

Cultivation:

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

Links:

• Den Virtuella Floran, Naturhistoriska riksmuseet, Stockholm

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