Rare Species Guide

  Synonyms

Woodsia oregana var. cathcartiana

  Basis for Listing

In Minnesota, Woodsia oregana ssp. cathcartiana (Oregon woodsia) is known to occur, or have occurred, at approximately 40 locations in 17 counties. Most of these occurrences are on bedrock outcrops in the northeastern portion of the state. There is also a concentration of records from granite bedrock exposures in the southwestern portion of the state, primarily in the Upper Minnesota Valley. There is concern for the southwestern populations because of increased rock-quarrying activities. Threats to other populations are largely unknown, though the expansion of recreational rock climbing has been suggested as a potential threat.

Until further survey work is completed for this species and threats to the populations are adequately assessed, it was deemed necessary to designate W. organa ssp. cathcartiana a species of special concern in 2013.

  Description

Woodsia oregana ssp. cathcartiana tends to grow erect or ascending, with persistent petiole bases of unequal lengths. They have brown or bicolored scales. The leaves (fronds) are 4-25 cm (2-10 in.) long and 1-4 cm (0.4-2.0 in.) wide. The petioles are not jointed. The blade is linear-lanceolate to narrowly ovate, pinnate-pinnatifid, sparsely to moderately glandular; the rachis has scattered glandular hairs and occasional hairlike scales. The pinnae are longer than wide and abruptly tapered to a rounded or broadly acute apex. The largest pinnae have 3-9 pairs of pinnules; the surfaces are glabrescent to moderately glandular. The pinnules are dentate and often shallowly lobed. The indusia are composed of narrow and usually filamentous segments.

  Habitat

In Minnesota, W. oregana ssp. cathcartiana occurs in crevices of bedrock outcrops, including cliffs and talus. In northeastern Minnesota (Border Lakes and North Shore Highlands subsections), it occurs on cliffs and talus consisting of a variety of crystalline bedrock types, including sandstone, basalt, and granite. In southwestern Minnesota, the habitat is primarily bedrock outcrops of gneiss and granite in the Minnesota Valley (Minnesota River Prairie Subsection) and Sioux quartzite in the Prairie Coteau (Inner Coteau and Coteau Moraines subsections). In the southeastern counties, it occurs on cliffs of limestone and sandstone (The Blufflands). These are typically dry and shaded or partially shaded habitats. Soil in the rock crevices is minimal and consists mostly of fine wind-blown particles, coarse rock fragments, and remnant organic material.

  Biology / Life History

As defined in The Flora of North America (Windham 1993), W. oregana is comprised of two subspecies that are chromosomally and biochemically distinct. In addition, the two taxa are nearly allopatric, with the diploid (subsp. oregana) confined to the Pacific Northwest and the tetraploid (subsp. cathcartiana) extending from the southwestern United States to eastern Canada. Isozyme studies indicate that it may be more appropriate to recognize these taxa as distinct species.

The habitat of Woodsia oregana ssp. cathcartiana tends to be xeric in nature, especially in dry and hot years. Under these conditions, the plants may become dry and shriveled before the end of their normal growing season. This condition is presumably intended to conserve moisture and does not harm the plant.

  Conservation / Management

This species is concentrated in a habitat (granite and sedimentary outcrops) that is experiencing increasing pressure from rock quarrying. There does not seem to be any way in which a bedrock exposure that supports a population of this species can be quarried without destroying the population. How often this conflict may arise and how such conflicts might be resolved are important questions that need to be addressed.

  Best Time to Search

With experience, this species can be identified by characteristics of the leaf, which is best seen in June, July, and August. In a particularly hot and dry summer, the leaves may senesce early and be brown and shriveled by August. Lacking experience with ferns, a searcher should plan to search in July, when reproductive structures are most likely to be present.

  Authors/Revisions

Welby Smith (MNDNR), 2018

(Note: all content ©MNDNR)

  References and Additional Information

Harris, F. 2009. Rock pools on the prairie: ephemeral pools on the prairie form amazing mini-ecosystems. Minnesota Conservation Volunteer 72(423):30-39.

Minnesota County Biological Survey. 2007. Native plant communities and rare species of the Minnesota River Valley counties. Division of Ecological Resources, Minnesota Department of Natural Resources, St. Paul. 153 pp.

Minnesota Department of Natural Resources. 2003. Field guide to the native plant communities of Minnesota: the Laurentian mixed forest province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 352 pp.

Minnesota Department of Natural Resources. 2005. Field guide to the native plant communities of Minnesota: the prairie parkland and tallgrass aspen parklands provinces. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 362 pp.

NatureServe. 2009. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia.

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

Windham, M. D. 1993. Woodsia. Pages 270-280 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 2. Oxford University Press, New York, New York.