Stems compact to creeping, erect to horizontal, with few to many persistent petiole bases of unequal lengths; scales often uniformly brown but at least some bicolored with dark central stripe and pale brown margins, narrowly lanceolate. Leaves 8--60 × 2.5--12 cm. Petiole light brown or straw-colored when mature, occasionally darker at very base, not articulate above base, relatively brittle and easily shattered. Blade lanceolate to ovate, 2-pinnate to 2-pinnate-pinnatifid proximally, moderately glandular, rarely somewhat viscid; many glandular hairs with thick stalks and distinctly bulbous tips; rachis with glandular hairs and scattered, often hairlike scales. Pinnae ovate-deltate to elliptic, 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, lacking nonglandular hairs or scales. Pinnules dentate, sometimes deeply lobed; margins nonlustrous, thin, with occasional glands, lacking cilia or translucent projections. Vein tips usually enlarged to form whitish hydathodes visible adaxially. Indusia of relatively broad, nonfilamentous segments, these multiseriate throughout, composed of ± isodiametric cells, entire or glandular along distal edge, concealed by or slightly surpassing mature sporangia. Spores averaging 35--47 µm. Woodsia obtusa comprises two cytotypes that are treated here as subspecies because they show subtle morphologic and ecological distinctions and tend to have different distributions. Tetraploid populations (subsp. obtusa ) are found throughout the eastern flora, commonly occurring on limestone. The diploid (subsp. occidentalis ) is found near the western edge of the species range, usually on sandstone and granitic substrates. Isozyme studies suggest that subsp. obtusa may have been derived from subsp. occidentalis through autopolyploidy (M. D. Windham 1993). The westernmost collections of Woodsia obtusa (all subsp. occidentalis ) come from the Wichita Mountains of Oklahoma and the Edwards Plateau of Texas. Reports of this species from the trans-Pecos region of western Texas are apparently based on misidentifications.
Rhizome-scales few, lance-linear, 2-3.5 נ0.3-0.6 mm, attenuate, sparingly glandular-fimbriate, with a dark central stripe when mature; lvs few, 25-55 cm; petiole stramineous, not articulate, sparingly glandular-hairy and scaly when young; blade lanceolate, 3.5-10 cm wide, slightly narrowed below, bipinnate-pinnatifid, the rachis glandular-hairy and sparingly scaly; pinnae 13-18 pairs, rather remote, subsessile, ovate or lance-ovate, sparsely glandular-hairy on the costae, costules, and veins; pinnules 6-13 pairs, oblong, rounded, deeply pinnatifid with 4-6 pairs of rounded, crenate segments; indusial segments 4-6, several cells wide, glandular-margined, incurved and covering the sporangia when young; 2n=152-156. Shady ledges and loose talus-slopes, mostly in circumneutral soil; Me. to Minn. and e. Nebr., s. to Fla. and Tex.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.