Home › Dennstaedtiaceae › Pteridium › Pteridium aquilinum (common bracken, eagle fern)

aquilinum – aquila (Latin), meaning eagle

Native range: worldwide

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Leaves:

  • large, solitary fronds
  • erect
  • deciduous
  • to 3 m. tall
  • triangular blades
  • 2–3 times pinnate
  • hairy
  • stipes:
    • stout
    • straw-colored to greenish
    • longer than the blades
  • pinna:
    • 10+ pairs
    • mostly opposite
    • the lowest pair narrowly to broadly triangular
    • upper ones progressively reduced and lance-shaped
    • ultimate segments round toothed
    • margins rolled under
  • many fronds (sometimes 75–100) clustered on a short, vertical rhizome

Pteridium aquilinum subsp pubescens 5361569

Reproduction:

  • alternation of generations
  • reproduces by spores visible April–October
  • sori:
    • marginal
    • continuous
    • covered by rolled leaf margin
    • indusium (membrane covering sori) not evident

Starr-100712-3187-Pteridium aquilinum subsp decompositum-sori-Holua Haleakala National Park-Maui (24747738190)

Other characteristics:

  • deciduous
  • fronds die back rapidly after the first fall frost
  • rhizomes:
    • spreading, much branched below ground surface
    • clothed with numerous hairs
    • can grow to 20’ long or more

Relevant info:

  • world’s most widespread fern, which may be explained in part by its many defenses

Ecology & Adaptations:

  • widely distributed throughout Washington
  • widely distributed throughout North America
  • circumboreal
  • common in moist to dry woods, open slopes and disturbed sites
  • spores dispersed by wind and water
  • adapted to dry conditions:
    • cuticular waxes seal plant surfaces against excessive water loss and are complex mixtures of very-long-chain aliphatics (carbon compounds without rings)
    • in redwood forest of northern CA, water in fog drip from canopy is absorbed through foliar uptake to stay hydrated during the rainless summer
    • mycorrhizae aid in water uptake
  • adapted to low nutrient conditions – mycorrhizae aid nutrient uptake
  • herbivore defense – fronds contain an unusually large and diverse number of chemical compounds that are toxic or deter and defend bracken against pathogens and herbivores, including carcinogens, mutagens, vitamin- decomposing enzymes, cyanide-releasing, insect- molting hormones, and tannins that interfere with digestion
  • ant-bracken mutualism:
    • nectaries containing sugars, proteins, and amino acids attract ants to fronds
    • the ants defend the bracken from generalist herbivores but not against those that specialize on bracken (sawflies, gall formers, mining insects) and avoid the impact of ants through their own chemical defenses or the location of feeding within the body of the fern