Gymnocarpium jessoense

Asian Oak Fern

Asian Oak Fern, Photo courtesy Wisconsin State Herbarium and Emmet J. Judziewicz

Asian Oak Fern
Photo courtesy Wisconsin State Herbarium
and Emmet J. Judziewicz

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


  • Gymnocarpium, from the Greek, gumnos (gymnos), "naked", and karpos (karpos), "fruit"; a reference to the lack of indusia.
  • jessoense, from the Latin, "of Jesso", a reference to Jesso or Yezo Island, the Japanese island now known as Hokkaido.
  • Common name from its Eurasian distribution.
  • Other common names include Nahanni Oak Fern, Northern Oak Fern, gymnocarpe du japon sous-espèce fréle (Qué), Idänimarre (Fin), Östbräken (Swe)


  • Kingdom Plantae, the Plants
    • Division Polypodiophyta, the True Ferns
      • Class Filicopsida
        • Order Polypodiales
          • Family Dryopteridaceae
            • Genus Gymnocarpium, the Oak Ferns
  • Taxonomic Serial Number: 524119
  • Also known as Gymnocarpium continentale, Dryopteris jessoensis, Aspidium dryopteris var. longulum, Gymnocarpium longulum, Gymnocarpium robertianum ssp. longulum
  • Our plants are classified as Gymnocarpium jessoense subspecies parvulum.
  • Hybrids between Gymnocarpium jessoense ssp. parvulum and Gymnocarpium dryopteris are usually found wherever these two species occur together, as they do in NE Minnesota. This hybrid, referred to as Gymnocarpium × intermedium is intermediate between the two parental species in leaf shape and glandularity.


  • A rare cousin of our common Oak Fern.
  • Fronds monomorphic and deciduous; 3"-15" tall
    • Petiole (leaf stalk) 2"-10", with moderately abundant glandular hairs.
    • Blade narrowly triangular to narrowly ovate, thrice-cut, 1¼"-5½", lower surface moderately glandular, upper surface smooth.
    • Rachis (axis) moderately to densely glandular.
    • Pinnae (primary leaflets) three per frond. Lower pair ¾"-3½"; strongly curved toward tip of frond.
    • Pinnules (secondary leaflets) on lower side of pinna midrib strongly curved toward tip of pinna.
  • Rootstalk 0.5mm-1.5mm in diameter.


  • Identifiable as an Oak Fern by its small size, delicate form, and three lobed frond.
  • Distinguished from common Oak Fern (Gymnocarpium dryopteris) by the glandular underside of the frond, where Oak Fern is smooth.
  • Distinguished from the closely related Northern Oak Fern (Gymnocarpium robertianum) by the smooth upperside of the frond, where the Northern Oak Fern is glandular, and by the strongly upswept lower leaflets, where those of the Northern Oak Fern are more closely perpendicular.
  • Field Marks
    • small size
    • triangular, three-part frond
    • presence or absence of glands on surface of frond
    • orientation of leaflets to axis of frond
    • orientation of subleaflets to midrib of leaflet


  • Alaska to the Northwest Territories, south to British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, Minnesota, Wisconsin, and the Upper Peninsula; Quebec and northern Maine.
  • Also Finland, northern Siberia, and Kazakhstan..


  • Cool, shale talus slopes; granitic cliffs and outcrops.






  • By spore and vegetatively by rhizome


  • By rhizome division


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



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Last Updated on 15 September, 2002