Rare Species Guide

  Synonyms

Woodsia scopulina

  Basis for Listing

As its common name implies, this fern is common in the Rocky Mountains of North America with several isolated populations scattered in mountainous or rocky habitats across other parts of the continent. This includes a few populations isolated in the Border Lakes region of Minnesota and Ontario.

In Minnesota, Woodsia scopulina ssp. laurentiana is primarily limited to the Rove Slate Formation at the eastern end of the Border Lakes region in Cook County. This area has landscape features not found elsewhere in Minnesota. There are several series of steep, east-west oriented valleys created by the preferential erosion of exposed slate that occurs between successive layers of harder diabase. The diabase-capped ridges between the valleys slope gently to the south but have precipitous northern faces rising 60-140 m (197- 460 ft.) above deep, cold lakes. These north-facing cliffs provide the habitat of W. scopulina ssp. laurentiana. Much of this area is now protected in the Boundary Waters Canoe Area Wilderness. In 2008, a new population was also found on a steep, north-facing cliff in the adjacent Vegetable Lakes Till Plain.

Woodsia scopulina ssp. laurentiana was discovered in the Rove Slate region in 1929 (Butters and Abbe 1953). Exploration in the 1930s and 1940s documented about 19 different sites. Frederick Butters and Ernst Abbe first visited many of these sites during their study of the flora of Cook County. They described the species as extremely localized-very abundant on some cliffs, rare on others, and absent from many. Nine of the early collection sites have been relocated since 1980 and 6 others were searched unsuccessfully; botanists have not revisited 4 sites. Seven additional W. scopulina ssp. laurentiana sites have recently been documented bringing the current total to 16 (plus 4 possible). The recent additions are the result of several years of intense and highly directed searches. It is not likely that many more sites will be found outside the species' known distribution area. Woodsia scopulina ssp. laurentiana was listed as a threatened species in Minnesota in 1984.

  Description

Woodsia scopulina ssp. laurentiana looks very similar to other members of the genus and requires close examination for positive identification. Sori (clusters of sporangia) are round and the indusium (flap or covering associated with the sorus) is borne beneath it. After spores are released, the indusium can be seen under a microscope as a few narrow, irregular segments of tissue. The stipe (leaf stalk) is not jointed so old remnant stipes vary in length and lack the thickened ends where a joint might have been (as in some other species in the genus). A distinctive feature of the leaf blade, at least on the underside, is the combined presence of minutely stalked glands and white hairs.

  Habitat

The bedrock in the Rove Formation where Minnesota populations of W. scopulina ssp. laurentiana occur is diabase and slate in a Precambrian terrain. It was previously thought that W. scopulina ssp. laurentiana preferred calcareous microhabitats in the slate formation, but they have also been found on the diabase. Plants invariably occur in cool, moist and shaded conditions, often on north-facing cliffs. They frequently occur on lower portions of a cliff face in vertical and horizontal cracks, and small ledges and chutes just above the talus slope. Plant associates include many common ferns such as Cystopteris fragilis (fragile fern), Dryopteris fragrans (fragrant fern), Polypodium virginianum (common polypody), W. ilvensis (rusty woodsia), and in a few cases, the rare fern, Asplenium trichomanes ssp. trichomanes (maidenhair spleenwort) (Gerdes 2001).

  Biology / Life History

Woodsia scopulina ssp. laurentiana is a perennial, herbaceous fern that grows in small clumps. The leaves turn brown in the fall but the bases of the stems remain attached to the rhizomes for a year or more. This condition is called marcescent.

The best time to search for W. scopulina ssp. laurentiana is from late June to early August, although this is somewhat dependent on exposure and aspect.

  Conservation / Management

This western species has a very limited amount of suitable cliff habitat in the Lake Superior region. Currently known populations are within the boundaries of the Superior National Forest. Even if these sites are protected from development, there is concern for W. scopulina ssp. laurentiana because the populations are concentrated in such a small geographic area. The cool, moist conditions they seem to require could be altered by global climate change or by forest management activities that alter the canopy, increase the risk of fire, introduce non-native species, or affect local run-off and erosion events. Also, cliffs are attractive to people for various reasons and cliff species are subject to injury, especially by recreational exploration of cliff bases, slopes, talus, and cliff tops. The fragile, highly unstable, fine talus zone at the base of cliff faces, especially sedimentary cliffs such as the Rove, is most vulnerable. Cliff top rims and edges are also highly vulnerable to trampling and trail development. It is very common to have trails established along the cliff rims in the Boundary Waters Canoe Area Wilderness Rove and cliffs elsewhere.

  Conservation Efforts in Minnesota

A systematic search of the primary habitat occupied by W. scopulina ssp. laurentiana in Minnesota has been nearly completed. As of 2008, only a small area in Cook County remains to be searched. New searches for this species are just beginning to occur in other portions of the Border Lakes subsection, but based on known information, the likelihood of finding many new populations is believed to be low. The survey work completed to date is a great contribution to conservation, giving land managers a sound basis for establishing protection plans.

  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.

Watson, P. J., and M. Vazquez. 1981. Comparative ecology of Woodsia scopulina sporophytes and gametophytes. American Fern Journal 71(1):3-9.