Dryopteris intermedia

Intermediate Wood Fern

Intermediate Wood Fern
Photo courtesy Wisconsin State Herbarium
and Emmet J. Judziewicz

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

Name:

• Dryopteris, from the Greek, drus (drys), "oak" and pteris (pteris), "fern", "fern of the oak wood"
• intermedia, from the Latin intermedius,"that is between, intermediate "
• Common name from
• Other common names include Evergreen Wood Fern, Fancy Wood Fern, Fancy Fern, Glandular Wood Fern, Dryoptère Intermédiaire, Dryoptère Spinuleuse (Qué)

Taxonomy:

• Kingdom Plantae, the Plants
• Division Polypodiophyta, the True Ferns
  • Class Filicopsida
    • Order Polypodiales
      • Family Dryopteridaceae, the Wood Ferns
        • Genus Dryopteris, the Wood Ferns
• Taxonomic Serial Number: 17538
• Also known as Aspidium intermedium, Aspidium spinulosum var. intermedium, Dryopteris austriaca var. intermedia, Dryopteris spinulosa var. concordiana, Dryopteris spinulosa var. intermedia, Thelypteris spinulosa var. intermedia

Description:

• A large, lacy, woodland fern.
• Fronds monomorphic, evergreen; 4"-8" × 12"-36"
  • Petiole (leaf stalk) 1/4-1/3 length of blade, scaly at least at base; scales scattered, tan.
  • Blade ovate, thrice-cut, and glandular.
  • Pinnae (primary leaflets) lanceolate-oblong and more-or-less in plane of blade; lowest pair lanceolate, and not reduced in size.
  • Pinnules (secondary leaflets) with toothed edges, teeth spiny; basal pinnules longer than adjacent pinnules, basal basiscopic pinnule (lowest downward pointing subleaflet on lowest pinnae) longer than basal acroscopic pinnule (lowest upward pointing subleaflet on lowest pinnae).
• Rootstalk green with tan scales
  • Roots black, wiry, and widely spreading; highly variable.
• Sori midway between midvein and margin of segments.
  • Indusia with minute stalked glandular hairs.

Identification:

• Identifiable as a Wood Fern by its larger size, thrice-cut fronds, and woodland habitat.
• Distinguished from the closely related and nearly identical Spinulose Woodfern (Dryopteris carthusiana) and Spreading Woodfern (Dryopteris expansa), (two species with which it once shared the common species designation of Dryopteris spinulosa), by the first downward pointing secondary leaflet (basiscopic pinnule) on the lowest primary leaflet (basal pinna) being shorter than the one next to it.
• Field Marks
  • thrice-cut, lacy fronds
  • relative lengths of pinnules (subleaflets) on lowest pair of pinnae (leaflets)

Distribution:

• Ontario to Newfoundland, south to Minnesota, Iowa, Missouri, Tennessee, Alabama, and Georgia

Habitat:

• Moist rich woods, ravines, and swamp margins.

Fire:

Associates:

• Trees: Red Maple (Acer rubrum), Paper Birch (Betula papyrifera), White pine (Pinus strobus), Bigtoothed Aspen (Populus grandidentata), Quaking Aspen (Populus tremuloides)
• Herbs: Blue Bead Lily (Clintonia borealis), Canada Mayflower (Maianthemum canadense)

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 supplier.

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