Roots not proliferous. Stems short-creeping or ascending, frequently branched; scales dark reddish brown to blackish throughout, narrowly deltate, 2--4 × 0.2--0.4 mm, margins entire to undulate or with widely spaced shallow teeth. Leaves monomorphic. Petiole reddish brown at base, green distally, lustrous, 1--5(--6) cm, 1/4--1/2(--1) times length of blade; indument of dark reddish brown to black, narrowly deltate scales grading into glandular hairs. Blade linear, 1-pinnate throughout, 2--13 × 0.6--1.2 cm, thin, glabrous or with sparse minute hairs; base slightly tapering or truncate; apex acute, not rooting. Rachis green throughout, dull, glabrous or with scattered hairs as on petioles. Pinnae in 6--21 pairs, deltate to rhombic; medial pinnae 5--6 × 4--5 mm; base obtuse and often inequilateral; distal margins crenate; apex rounded to acute. Veins free, evident. Sori 2--4 pairs per pinna, on both basiscopic and acroscopic sides. Spores 64 per sporangium. 2 n = 72. Limestone and other basic rocks; 0--4000 m; Greenland; Alta., B.C., N.B., Nfld., N.W.T., N.S., Ont., P.E.I., Que., Yukon; Alaska, Calif., Colo., Idaho, Maine, Mich., Mont., Nev., N.Y., Oreg., S.Dak., Utah, Vt., Wash., Wis., Wyo. Hybridization between Asplenium trichomanes-ramosum and A . trichomanes produces the fertile allotetraploid A . adulterinum , which occurs on Vancouver Island.
Rhizome 1 mm thick, the scales few, 3-4 mm; lvs numerous, 5-15 cm, the petiole to 4 cm, brownish at base, green distally; blade thin, not evergreen, linear-oblong, pinnate throughout, to 1.5 cm wide, acute, scarcely narrowed toward the base, the rachis green and flattened; pinnae 9-16 pairs, subopposite at base, alternate upwardly, sessile, 3-9 נ2-4 mm, obtuse, cuneate at base, bluntly toothed, not auriculate; 2n=72. Shaded limestone rocks; circumboreal, in Amer. s. to N.S., n. Vt., n. N.Y., Wis., Colo., and Wash.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.