Sp. Pl. 2: 1080. 1753.
Roots not proliferous. Stems short-creeping, often branched; scales black throughout or with brown borders, lanceolate, 2–5 × 0.2–0.5 mm, margins entire to denticulate. Leaves monomorphic. Petiole reddish-brown or blackish brown throughout, lustrous, 1–4 (–7) cm, 1/6–1/4 length of blade; indument absent or of black, linear-lanceolate or filiform scales at base. Blade linear, 1-pinnate, 3–22 × 0.5–1.5 cm, thin, glabrous or sparsely pubescent; base gradually tapered; apex narrowly acute, not rooting. Rachis reddish-brown throughout, lustrous, glabrous or nearly so. Pinnae in 15–35 pairs, oblong to oval; medial pinnae 2.5–8 × 2.5–4 mm; base broadly cuneate, with or without low, rounded acroscopic auricle; margins shallowly crenate to serrate or ± entire; apex obtuse. Veins free, evident. Sori 2–4 pairs per pinna, on both basiscopic and acroscopic sides. Spores 64 per sporangium. 2n = 72, 144.
B.C., N.B., N.S., Nfld. and Labr. (Nfld.), Ont., Que., Ala., Alaska, Ariz., Ark., Calif., Colo., Conn., Del., Ga., Ill., Ind., Kans., Ky., La., Maine, Mass., Md., Mich., Minn., Mo., N.C., N.H., N.J., N.Mex., N.Y., Nebr., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Va., Vt., W.Va., Wash., Wis., Wyo., Worldwide
In North America, as in Europe, Asplenium trichomanes consists of diploid and tetraploid cytotypes, treated here as subspecies. Asplenium trichomanes subsp. trichomanes, the diploid, is found on noncalcareous rocks. In the southwestern United States it occurs at high elevations. Asplenium trichomanes subsp. quadrivalens, the tetraploid, grows on calcareous substrates and has a more northern distribution (R. C. Moran 1982). Triploid hybrids are known between the diploids and tetraploids (R. C. Moran 1982; W. H. Wagner Jr. and F. S. Wagner 1966).
Subspecies 4 (2 in the flora).