Rare Species Guide

  Basis for Listing

Woodsia glabella (smooth woodsia) is a small delicate fern characteristic of arctic and subarctic regions of North America and Eurasia. It occurs sporadically in a few boreal and alpine habitats as far south as the mountains of New England. There is also an isolated series of small populations along the North Shore of Lake Superior (North Shore Highlands Subsection) and the Border Lakes region (Border Lakes Subsection)   that are far removed from the main range of the species.

Woodsia glabella was discovered in Minnesota in 1929 by Frederick Butters on the Rove Formation (shale, argillite, greywacke) cliffs near Grand Portage in Cook County. It was rediscovered there in the 1930s and found at another site about 12 km (7.5 mi.) to the north. Butters and Abbe (1953) described the presence of W. glabella in that general area to be extremely local and rare. A 1947 collection along the Gooseberry River in Lake County was not relocated despite recent searches.

Over a dozen new locations of this species were discovered from 1994 to 2001 as a result of intensive, systematic searches. At the new locations, W. glabella appears to occur just as Butters and Abbe described; there are rarely many plants (10 or 20) at a given site, and they occur in just a few patches. Because the plants are so few and so localized, W. glabella could easily be eliminated at many sites by natural processes such as erosion (for example through rock slides) or by recreational activities (such as rock climbing and scrambling). Woodsia glabella was listed as a threatened species in Minnesota in 1984.

  Description

Woodsia glabella is an inconspicuous fern that can be difficult to identify unless reproductive structures are present. Sori (clusters of sporangia) are round, and the unusual indusium (usually a flap or covering associated with the sorus) is a tiny disk with slender hairs curling up from the margin. The stipe (leaf stalk) is green and jointed near the base, the joint appearing as a dark thickened ring. After fronds have fallen off, the stubs of the stipe bases are all about the same length. The only other jointed Woodsia species are W. ilvensis (rusty woodsia) and W. alpina (alpine woodsia), but they both have scaly stipes or hairy fronds. Woodsia glabella is glabrous (without hairs) and scaleless.

  Habitat

Earlier W. glabella discoveries were from habitats described as a wet calcareous slate cliff and a north-facing cliff. Recent, newly discovered sites indicate that W. glabella is not restricted to calcareous microhabitats and there is not a strong pattern of association with a particular rock type. The microhabitat in which it occurs is typically crevices in moist, north-facing cliffs (often diabase bedrock), sometimes with a slight overhanging ledge or some other feature that gives the plants a little extra protection from the wind or ice. Other plants that are found on the shady cliffs include Thuja occidentalis (northern white cedar), Betula cordifolia (heart-leaved birch), Cystopteris fragilis (fragile fern), Carex eburnea (ivory sedge), Saxifraga paniculata (encrusted saxifrage), Campanula rotundifolia (harebell), and a variety of mosses.

  Biology / Life History

Woodsia glabella is a fern that grows in clumps on shady rock ledges and cliffs. The leaves turn brown and wither in the fall, but the bases of the stems remain attached to the rhizomes. Very little else is known about the species.

  Conservation / Management

This northern species has a very limited amount of suitable cliff habitat in the Lake Superior region. The currently known W. glabella populations occur mostly on land in state ownership or land serving a conservation function, but others are on private land. Even if the sites are protected from development, however, there is concern for this species, because the populations are small and concentrated in a limited geographic area. The cool, moist conditions that it seems to require could be altered by global climate change. Certain forest management practices or other activities that increase the risk of fire or decrease the shade or cool microclimate produced by the surrounding forest could impact habitat conditions. Also, populations of W. glabella and other rare cliff species that are located on larger, taller cliffs can be subject to injury by recreationists, particularly rock climbers.

  Best Time to Search

The best time to search for Woodsia glabella is when it is fully mature, from mid-June through mid-September.

  Conservation Efforts in Minnesota

Systematic field surveys for W. glabella in northeastern Minnesota have been recently completed by the Minnesota Biological Survey. This is a great contribution to conservation, giving land managers a sound basis for establishing protection plans. However, because W. glabella is typically found in small isolated patches in rugged areas of cliffs and gorges, it is quite possible, even likely, that undiscovered populations exist even in areas already searched.

  Authors/Revisions

Welby R. Smith (MNDNR), 2021; Lynden Gerdes (MNDNR), 2008

(Note: all content ©MNDNR)

  References and Additional Information

Butters, F. K., and E. C. Abbe. 1953. A floristic study of Cook County, northeastern Minnesota. Rhodora 55:21-55.

Gerdes, L. B. 2001. A contribution to the flora of the Rove Slate Bedrock Complex Landtype Association, northern Cook County, Minnesota, U.S.A. Thesis, Michigan Technological University, Houghton. 79 pp.

Smith, W. R. 2023. Ferns and lycophytes of Minnesota: the complete guide to species identification. University of Minnesota Press, Minneapolis. 368 pp.

Tryon, Jr., R. M. 1948. Some Woodsias from the North Shore of Lake Superior. American Fern Journal 38(4):159-170.