Canad. Naturalist & Quart. J. Sci. 2: 91. 1865.
Stems compact, erect to ascending, with few-to-many persistent petiole bases of unequal lengths; scales uniformly brown or bicolored with dark central stripe and pale-brown margins, ovate to narrowly lanceolate. Leaves 9–35 × 1–8 cm. Petiole usually reddish-brown to dark purple proximally when mature, not articulate above base, relatively brittle and easily shattered. Blade lanceolate to linear-lanceolate, 2-pinnate proximally, moderately glandular, rarely somewhat viscid; most glandular-hairs with thick stalks and distinctly bulbous tips; rachis usually with abundant glandular and nonglandular hairs. Pinnae lanceolate-deltate to ovate, longer than wide, abruptly tapered to a rounded or broadly acute apex, occasionally attenuate; largest pinnae with 5–14 pairs of pinnules; abaxial and adaxial surfaces glandular and sparsely villous, with flattened, multicellular hairs concentrated along midribs. Pinnules dentate, often shallowly lobed; margins nonlustrous, thin, slightly glandular and occasionally ciliate with isolated, multicellular hairs, lacking translucent projections. Vein tips slightly (if at all) enlarged, barely visible adaxially. Indusia of filamentous or nonfilamentous segments, these multiseriate proximally, often uniseriate distally, composed of ± isodiametric cells, concealed by or slightly surpassing mature sporangia. Spores averaging 39–57 µm.
Alta., B.C., Ont., Que., Sask., Yukon, Alaska, Ariz., Ark., Calif., Colo., Idaho, Ky., Mont., N.C., Nev., Oreg., S.Dak., Tenn., Utah, Va., W.Va., Wash., Wyo., only in the flora
Woodsia scopulina shows substantial variation in leaf size, shape, and dissection, and in the abundance of multicellular hairs on the pinnae. Although much of this variation seems to be environmentally induced, recent studies (M. D. Windham 1993) have identified three chromosomal/morphologic variants that are treated here as subspecies. Diploid populations of W. scopulina are divisible into two groups, one of which (subsp. scopulina) is scattered throughout the mountainous regions of western North America while the other (subsp. appalachiana) is confined to montane habitats in the southeastern United States. These taxa seem amply distinct (T. M. C. Taylor 1947) and might be considered separate species if not for the existence of populations in the Great Lakes region and western cordillera that tend to bridge the morphologic and geographic gap between them. These intermediate populations (subsp. laurentiana) appear to be uniformly tetraploid and may have arisen through ancient hybridization between subsp. scopulina and subsp. appalachiana. In regions where subsp. laurentiana is sympatric with subsp. scopulina, the two taxa are rarely found growing together, suggesting that they differ in their ecological tolerances and/or habitat requirements.
|1||Scales of stems and petiole bases narrowly lanceolate, mostly bicolored with broad, usually continuous, dark central stripe; longest hairs on pinnae composed of 5-8 cells; indusial segments broad, not at all filamentous.||Woodsia scopulina subsp. appalachiana|
|1||Scales of stem and petiole bases ovate-lanceolate, mostly concolored or weakly bicolored with narrow, often discontinuous, dark central stripe; longest hairs on pinnae composed of 2-5 cells; indusial segments narrow, often filamentous distally.||> 2|
|2||Spores averaging 42-50 µm; stem and petiole base scales usually concolored or with a few isolated, dark, occluded cells.||Woodsia scopulina subsp. scopulina|
|2||Spores averaging 50-57 µm; at least some stem and petiole base scales with clusters of dark, occluded cells near center forming narrow, usually discontinuous stripe.||Woodsia scopulina subsp. laurentiana|
"thick" is not a number.