Dryopteris species

The Wood Ferns

Fragrant Fern
Jap Lake, BWCAW
Photo © 2001 by Earl J.S. Rook

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"
• Common name from the preferred woodland habitat of most of the genus.
• Other common names include Shield Fern, Dryoptère (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: 17519
• North Country Species
  • carthusiana, Spinulose Wood Fern
  • cristata, Crested Wood Fern
  • expansa, Spreading Wood Fern
  • fragrans, Fragrant Fern
  • intermedia, Intermediate Wood Fern
  • marginalis, Marginal Shield Fern (TH-MN)
• Over 250 species worldwide; most in temperate Asia.

Description:

• A group of classically "fern-like" ferns, of the sort one might find at the florist shop.
• Fronds monomorphic, fertile and sterile fronds virtually identical.
  • Petiole (leaf stalk) stout and scaly; often growing in tufts.
  • Blades often leathery, dark green, much cut; occasionally evergreen. Veins free, forked, ending short of the edge of the leaflet.
  • Pinnae (primary leaflets) toothed and deeply cut.
  • Pinnules (secondary leaflets) toothed and deeply cut.
• Rootstalk coarse and scaly, creeping.
• Sori round, numerous, and attached to veins; in a single row between leaflet edge and midrib.
  • Indusia prominent and kidney-shaped.
  • Spores brownish.

Identification:

• Field Marks
  • Habitat; these are typically woodland ferns.
  • Size; these are typically large ferns
  • Dissection; these are typically lacy, thrice-cut ferns

  Dryopteris ID for the North Country

• The Wood Ferns tend, not surprisingly, to be found growing on the ground in wooded places. There are two exceptions in our area.
• If you have a small (under 10"), fragrant fern growing in rock or on a cliff, and it is not one of the typical Cliff Ferns (Woodsia spp.) or the rock-loving Common Polypody (Polypodium virginiana), then it is probably Dryopteris fragrans, Fragrant Fern. Look for the grey/brown remnants of old fronds forming conspicuous clumps at the base of the fern.
• If you have a wetland fern, with tall, narrow fronds and leaflets which are very widely spaced from one another along the leafstalk and those leaflets are twisted so as to not lie on the same plane as the frond, then you have Dryopteris cristata, Crested Shield Fern.
• If you have a classic, lacy terrestrial fern more than 10" tall, with twice or thrice cut foliage, then it is likely one of three North Country Wood Ferns. The key to distinguishing among these closely related species (once considered but a single species, Dryopteris spinulosa) is to compare the basal pinnules of basal pinnae with the adjacent pinnules. (OK, in plain English, look closely at the lowest leaflet on the frond. It will have several secondary leaflets, all on the plane of the frond itself, some pointing upward, towards the tip of the frond, and some pointing downward, towards the base of the frond.)
• Look at the first downward pointing secondary leaflet (pinnule) on the lowest primary leaflet (pinna). If that first subleaflet is shorter than the one next to it, then you have Dryopteris intermedia, Intermediate Wood Fern.
• If that first downward pointing secondary leaflet is longer than the downward pointing subleaflet next to it, then you have to look at where it is attached in relation to the upward pointing subleaflets on the same primary leaflet.
  • If that first large downward pointing subleaflet is attached at or very near to the point of attachment of the first upward pointing subleaflet, then you have Dryopteris carthusiana, Spinulose Woodfern.
  • If on the other hand, that first large downward pointing subleaflet is attached at a point much closer to the second upward pointing subleaflet than the first, you have Dryopteris expansa, Spreading Woodfern.
• Confirm your ID by looking for some of the other characteristics of these three confusing ferns:
  • Dryopteris carthusiana, Spinulose Woodfern, First basal basiscopic pinnule not much wider than 1st acroscopic pinnule on basal pinnae; blades ovate-lanceolate
  • Dryopteris expansa, Spreading Woodfern, First basal basiscopic pinnule 2 times width of 1st acroscopic pinnule on basal pinnae; blades ovate-deltate. Petiole scales tan, with dark central stripe; leaves erect to slightly arching
  • Dryopteris intermedia, Intermediate Wood Fern,
• If your speciman doesn't quite seem to fit these characteristics, consider that you may have Dryopteris marginalis, Marginal Shield Fern, classified as Threatened in Minnesota. While it has not been collected from our area, it is known from similar habitat in northwestern Wisconsin and on Isle Royale, and should not be completely unexpected in northeastern Minnesota. It is distinguished from more typical Wood Ferns (Dryopteris sp.) by its leathery texture and its characteristic sori (fruitdots), neatly arranged along the margins of the leaflets.

Distribution:

• Alaska to Newfoundland and Greenland, south to
• Also northern Europe and Asia

Habitat:

• Typically terrestrial, rarely on rock.

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 or at local nurseries.

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