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Spreading Woodfern (Dryopteris expansa)

Life history

Species overview

Spreading Woodfern (Dryopteris expansa), a Wisconsin Special Concern plant, is found in cool coniferous (balsam-fir, white cedar, hemlock) to mixed forests, sometimes in cold canyons. The optimal identification period for this species is late May through late September.

Synonyms: Aspidium spinulosum var. americanum, Dryopteris assimilis, D. dilatata, D. dilatata ssp. Americana, D. spinulosa var. americana, D. spinulosa var. dilatata, Nephrodium expansum, Thelypteris spinulosa var. americana


  • Distinguishing characteristics: Stipe base scales pale brown, usually with a distinctly darkened, broad central strip or basal area; lower portion of basal pinnules 2 to 3 times longer than the upper portion of the basal pinnules; indusia eglandular.
  • Flower characteristics:
  • Fruit characteristics: Sori round, protected by a reniform indusium, appear in a single series on each side of segment midrib.
  • Leaf characteristics: Lanceolate to ovate-lanceolate, 20 to 60 cm long, 15 to 30 cm wide, broadest above the base, acute-acuminate at the base and apex, 3-pinnate-pinnatifid at the base, 2-pinnate-pinnatifid above the base; pinnae and the pinnules nearly equilateral, except the basal pinnae expanded; basal basiscopic pinnules (downward pointing, or lower portion of basal pinnules) 2 to 3 times longer than the basal acroscopic ones (upward pointing, or upper portion of the basal pinnules); pinnule segments and lobes spinulose, the laminae eglandular or slightly glandular.


  • Blooming phenology:
  • Fruiting phenology: late summer
  • Optimum time to identify: The optimal identification period for this species is late May through late September


  • Growth form: Fern
  • Vegetative reproduction: Rhizomatous
  • Life cycle: Perennial
  • Comments: Associated Species: Abies balsamea, Thuja occidentalis, Tsuga canadensis, Acer rubrum, A. saccharum, A. spicatum, Betula alleghaniensis, Polystichum braunii, Dryopteris cathusiana, D. intermedia.

State status

Status and Natural Heritage Inventory documented occurrences in Wisconsin

The table below provides information about the protected status - state and federal - and the rank (S and G Ranks) for Spreading Woodfern (Dryopteris expansa). See the Working List Key for more information about abbreviations. Counties shaded blue have documented occurrences for this species in the Wisconsin Natural Heritage Inventory database. The map is provided as a general reference of where this species has been found to date and is not meant as a range map.

Documented locations of Dryopteris expansa in the Natural Heritage Inventory Database as of July 2015.

Summary Information
State StatusSC
Federal Status in Wisconsinnone
State RankS2
Global RankG5
Tracked by NHIY

Habitats and landscapes

The Natural Heritage Inventory has developed scores indicating the degree to which each of Wisconsin's rare plant species is associated with a particular natural community or ecological landscape. This information is similar to that found in the Wildlife Action Plan for animals. As this is a work in progress, we welcome your suggestions and feedback.

General habitat information

  • Habitat description: Found in cool coniferous (balsam-fir, white cedar, hemlock) to mixed forests, sometimes in cold canyons.
  • Soils: Moist, often rocky soils.

Natural communities

This table lists the natural communities that are associated with Spreading Woodfern. Scores for natural community associations are: "significant" association (score=3), "moderate association" (score=2) or the species can be present but is only weakly associated with the community (score=1).

Ecological landscapes

This table lists the ecological landscape association scores for Spreading Woodfern. The scores (3=High, 2=Moderate, 1=Low, 0=None) also correspond to the map.

Map of the Ecological Landscapes of Wisconsin.

Species guidance

The Endangered Resources Program has developed avoidance measures and management guidelines for plants on the Natural Heritage Working List. These are a work in progress, and we welcome your suggestions and feedback. Sources used in developing this information can be found here.

Avoidance measures

These are specific actions designed to avoid "take" (mortality) of this species.

  • Avoid cool, moist, rocky areas in forests where this species has been reported.
  • Avoid direct disturbance to sensitive microsites such as seeps, cliffs, and moss-covered boulders.
  • Avoid broadcast spraying of herbicides; use care with spot spraying.
  • Avoid known individual plant locations and conduct operations elsewhere when they are least likely to cause damage. Ideally, this would involve frozen, snow-covered ground. However, in areas of the state where frozen conditions are unreliable, very dry soils late in the growing season might be the best available alternative. Consult with a biologist, if needed.

Management guidance

Management guidelines are additional considerations that may help maintain or enhance habitat for this species

  • Although maintaining high overall forest canopy is important, silvicultural techniques which open small gaps in the canopy may be beneficial to this species.
  • Maintain structural characteristics of old growth forests such as downed logs and other coarse woody debris.


Spreading Woodfern Photo.

Photo © R.C. Moran.

Spreading Woodfern Photo.

Photo by  staff, Wisconsin DNR.

Support for Wisconsin's rare plant information has been provided by the Division of Forestry, the Endangered Resources Fund and the Wisconsin Rare Plant Preservation Fund. To donate, visit the Natural Resources Foundation of Wisconsin [exit DNR].

Last revised: Wednesday, May 05, 2021
Southwest Savanna Southern Lake Michigan Coastal Western Coulees and Ridges Southeast Glacial Plains Central Sand Hills Central Lake Michigan Coastal Central Sand Plains Northern Lake Michigan Coastal Northern Lake Michigan Coastal Northeast Sands Western Prairie North Central Forest Northern Highlands Northwest Lowlands Northwest Sands Northwest Lowlands Superior Coastal Plains Forest Transition