Woodsia alpina (Bolton) S.F. Gray
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Basis for Listing
Although there are a number of records of Woodsia alpina (alpine woodsia) in Minnesota, they are all from three counties in the northeast corner of the state (Northern Superior Uplands Section). All but five of the locations are along the shore of Lake Superior (North Shore Highlands Subsection), where development pressures are very great and increasing every year. Of particular concern are issues related to trail and road construction, recreational rock climbing, and timber management. These issues are especially problematic, because most of the W. alpina locations contain only a few plants, and extirpations could occur as a result of even small disturbances. Woodsia alpina was listed as special concern in Minnesota in 1996. A subsequent reevaluation of its rarity and threats to its habitat resulted in its status being elevated to threatened in 2013.
Woodsia alpina is a small, leafy, rock fern. The rhizome is compact, with numerous, persistent petiole bases. The frond is typically 15 cm (6 in.) high by 2 cm (0.8 in.) wide and deciduous, with a blade/stipe ratio of 2:1 to 3:1. The stipe has a persistent base, above which it articulates at a swollen node half-way up. The stipe is brown or black when mature and has red-brown, lanceolate scales at the base. The blade is 1-pinnate-pinnatifid, narrowly lanceolate to ovate-lanceolate, broadest below the middle, herbaceous, and bright green, with long, fine, red-brown hairs. The pinnae consist of 8 to 15 pairs; the largest pinnae, with 1 to 3 pairs of pinnules; the shorter ones, merely fan-shaped. The margins are nearly entire; the veins free, simple or forked. The sori are round and located near the margin. The indusia have filamentous segments enveloping the sori.
Woodsia alpina is found in crevices and on small ledges of moist, partially shaded cliffs. The cliffs are composed of circumneutral to weakly alkaline bedrock, including basalt and diabase. They occur mostly in two settings: cool river gorges near Lake Superior and sheltered Lake Superior shorelines that are not exposed to storm waves and ice scouring. A few populations occur on cliffs located further inland as well. The main range of this species is in arctic habitats, far to the north of Lake Superior. The occurrence of this species in the Lake Superior region (including Minnesota) is considered a major disjunction from its main range (Soper and Maycock 1963).
Biology / Life History
Molecular studies indicate that W. alpina is an allotetraploid (fertile hybrid) that was derived from W. glabella (smooth woodsia) and W. ilvensis (rusty woodsia) (Windham 1993). It is a perennial, however, it is not known how long individual plants may live.
Conservation / Management
Populations of W. alpina tend to be small and are usually restricted to specific portions of cliff features that may be separated from similar features by several meters (yards) or several kilometers (miles). This makes it difficult to define populations and to delineate habitat. For this reason, it may be necessary to carefully inspect all potential habitats near known populations if any management or development is contemplated.
Best Time to Search
The best time to search for W. alpina is when spores are present, from mid-June through September.
Welby Smith, MN DNR, 2008 and 2017
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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, Michigan. 79 pp.
Lakela, O. 1965. A flora of northeastern Minnesota. University of Minnesota Press, Minneapolis, Minnesota. 541 pp.
Lellinger, D. B. 1985. A field manual of the ferns and fern-allies of the U.S. & Canada. Smithsonian Institution Press, Washington, D.C. 389 pp.
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