Gymnocarpium species

Oak Ferns

Oak Fern
West Fern Lake, BWCAW, 1994
Photo courtesy Lowell Anderson

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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.
• Other common names include gymnocarpe (Qué)

Taxonomy:

• Kingdom Plantae, the Plants
  • Division Polypodiophyta, the True Ferns
    • Class Filicopsida
      • Order Polypodiales
        • Family Dryopteridaceae
          • Genus Gymnocarpium, the Oak Ferns
• Taxonomic Serial Number: 17578
• 8 species worldwide, in temperate North America and Eurasia; 5 in North America.
• North Country species
  • dryopteris, Oak Fern
  • jessoense, Asian Oak Fern
  • robertianum, Northern Oak Fern

Description:

• A group of small, delicate ferns of forest floor and rocky places.
• Fronds monomorphic and deciduous.
  • Petiole (leaf stalk) about 1½-3 times length of blade, base not swollen.
  • Blade broadly triangular or ovate, twice to thrice-cut, reduced to partially cut tip.
  • Pinnae (primary leaflets) three, with lowest pair longest and stalked.
  • Pinnules (secondary leaflets) on basiscopic (downward pointing) side of leaflet longer than those on acroscopic (upward pointing) side.
• Rootstalk long-creeping, stolons absent.
• Sori more-or-less round, in a single row between midrib and leaf edge.
  • Indusia absent
  • Spores brownish

Identification:

• Identifiable as an Oak Fern (Gymnocarpium species) by its small size, delicate form, and three lobed frond.
• Field Marks
  • presence or absence of glands on surface of frond
  • orientation of leaflets to axis of frond
  • orientation of subleaflets to midrib of leaflet

Gymnocarpium ID for the North Country

• Examine both surfaces of the frond for tiny glands.
  • If the frond is essentially smooth you have our common Oak Fern (Gymnocarpium dryopteris).
  • If the upper surface of the frond is smooth, but the lower surface is glandular, you have Asian Oak Fern (Gymnocarpium jessoense). The lower pair of leaflets will curve strongly toward the tip of the frond, and their downward pointing subleaflets will curve toward the tip of the leaflet. Asian Oak Fern, despite its name a Minnesota native, has been found in Cook and Lake Counties in our area but not St. Louis.
  • If the frond is glandular on the upper as well as the lower surface, you have Northern Oak Fern (Gymnocarpium robertianum). The lower pair of leaflets will be more-or-less perpendicular to the frond axis, and their downward pointing subleaflets more-or-less perpendicular to the central rib of the leaflet. Northern Oak Fern has been found in St. Louis and Lake Counties in our area but not Cook.

Distribution:

Habitat:

Fire:

Associates:

History:

Uses:

Reproduction:

• By spore and vegetatively by rhizome

Propagation:

• By rhizome division

Cultivation:

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

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