Stems erect to occasionally ascending. Leaves erect, not arching except at tip, 1--6 dm; bulblets absent. Petiole 1/10--1/6 of blade, densely scaly; scales light brown, gradually diminishing in size distally. Blade linear, often widest above middle, 1-pinnate, base narrowed. Pinnae oblong to lanceolate to falcate, proximal pinnae ± deltate, rarely overlapping, in 1 plane, 0.5--3 cm, base truncate to oblique, acroscopic auricle well developed; margins serrulate-spiny with teeth spreading; apex acute, subapical tooth hardly smaller than apical tooth; microscales dense, on abaxial surface only. Indusia entire or minutely dentate-erose. Spores dark brown. 2 n = 82. In rock crevices or at base of boulders, mostly in boreal and subalpine coniferous forests or alpine regions; 0--3200 m; Greenland; Alta., B.C., Nfld., N.S., Ont., Que., Yukon; Alaska, Ariz., Calif., Colo., Idaho, Mich., Minn., Mont., Nev., Oreg., Utah, Wash., Wis., Wyo. The hybrid between Polystichum lonchitis and P . acrostichoides (= P . × hagenahii Cody) is discussed under P . acrostichoides . The hybrid with P . braunii (= P . × meyeri Sleep & Reichstein) is discussed under P . braunii . In the Georgian Bay area of Ontario, P . lonchitis hybridizes with Dryopteris goldiana to produce the peculiar × Dryostichum singulare W. H. Wagner (W. H. Wagner Jr., F. S. Wagner et al. 1992). The spiny spores of P . lonchitis are distinctive and distinguish this from dwarfed forms of other 1-pinnate species.
Rhizome erect or ascending; lvs 2-6 dm, the petiole very short; blade rigid, lance-linear, 3-7 cm wide, pinnate, gradually narrowed below; pinnae alternate, 25-40 pairs, lanceolate (the reduced lower ones subtriangular), acuminate, sharply auricled at the upper base, scaly beneath, darker green and scaleless above; fertile pinnae like the sterile; sori in a single row on each side of the midrib; indusium lacerate; 2n=82. Cool shaded rocks and hillsides, mostly on limestone; circumboreal, s. to N.S., Que., Ont., Mich., and Calif.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.