Gymnocarpium robertianum

Northern Oak Fern

Northern Oak Fern
Photo Courtesy Wisconsin State Herbarium
and Michael R. Penskar

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

Name:

• Gymnocarpium, from the Greek, gumnos (gymnos), "naked", and karpos (karpos), "fruit"; a reference to the lack of indusia
• robertianum, from the Latin, "of Robert", a reference to Robert II ("the Pious"), king of France from 996 to1031.
• Common name from its range relative to the other Oak Ferns.
• Other common names include Limestone Fern, Limestone Oak Fern, Scented Oak Fern, Gymnocarpe de Robert, Polypode du Calcaire (Fr), Kalkbräken (Swe), Kalktelg (Nor), Kalk-Egebregne (Dan), Kalkki-Imarre (Fin), Ruprechtsfarn, Storchschnabelfarn (Ger), Mirigyes Tölgyespáfrány (Hun), Cienistki (Zachylki) Roberta (Pol)

Taxonomy:

• Kingdom Plantae, the Plants
  • Division Polypodiophyta, the True Ferns
    • Class Filicopsida
      • Order Polypodiales
        • Family Dryopteridaceae
          • Genus Gymnocarpium, the Oak Ferns
• Taxonomic Serial Number: 17581
• Also known as Dryopteris robertiana, Gymnocarpium dryopteris var. pumilum, Gymnocarpium jessoense, Phegopteris robertianum, Polypodium robertianum, Thelypteris robertiana

Description:

• A small and uncommon limestone loving northern fern
• Fronds usually 4"-20" long, growing parallel to the ground
  • Petiole (leaf stalk) 2"-13" long, with numerous glandular hairs.
  • Blade broadly triangular, 2"-7½" long, twice to thrice cut, usually firm and robust; surfaces moderately to densely glandular. Clearly composed of three lobes or leaflets, with that in the center being significantly larger than the two on either side.
• Roots adventitious (fibrous)

Identification:

• Identifiable as an Oak Fern by its small size, delicate form, and three lobed frond
• Distinguished from common Oak Fern (Gymnocarpium dryopteris) by its dominant central leaflet or lobe and its glandular frond surfaces. The three lobes of the Oak Fern are roughly equal in size and its fronds smooth.
• Distinguished from the closely related Asian Oak Fern (Gymnocarpium jessoense) by the lower pair of leaflets more-or-less perpendicular to the frond axis, and their downward pointing subleaflets more-or-less perpendicular to the central rib of the leaflet. The lower pair of leaflets and their downward pointing subleaflets curve strongly toward the tip of the frond and leaflet respectively on the Asian Oak Fern.
• Northern Oak Fern has been found in St. Louis and Lake Counties in our area but not Cook.
• Field Marks
  • small size
  • triangular, three-part frond
  • large central leaflet
  • presence or absence of glands on surface of frond
  • orientation of leaflets to axis of frond
  • orientation of subleaflets to midrib of leaflet

Distribution:

• Manitoba to Newfoundland, south to Minnesota, Iowa, Wisconsin, and Michigan.
• Also Europe and the Caucasus Mountains of Asia.

Habitat:

• Limestone and shale ledges and rock slopes across northern North America.
• Calcareous substrates; limestone pavement, outcrops, and cliffs; cedar swamps.

Fire:

Associates:

History:

Uses:

Reproduction:

• By spore; vegetatively by rhizome

Propagation:

• By rhizome division

Cultivation:

• Hardy to USDA Zone 2 (average minimum annual temperature -50ºF)
• Cultural Requirements
• Shade to part sun
• Average garden soil; does well on limestone
• Good for naturalizing the woodland shade garden
• Said to be easy to grow
• Rarely offered and difficult to obtain commercially.

Links:

• Den Virtuella Floran, Naturhistoriska riksmuseet, Stockholm

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