Western oak fern

Polypodium dryopteris Linnaeus var. disjunctum Ruprecht, Distr. Crypt. Vasc. Ross., 52. 1845; Dryopteris disjuncta (Ruprecht) C. V. Morton; Gymnocarpium dryopteris (Linnaeus) Newman subsp. disjunctum (Ruprecht) Sarvela; G. dryopteris var. disjunctum (Ruprecht) Ching

Stems 1--3 mm diam.; scales 2--4 mm. Fertile leaves usually 20--68 cm. Petiole 12--44 cm with sparse glandular hairs distally; scales 2--6 mm. Blade broadly deltate, 3-pinnate-pinnatifid, 8--24 cm, lax and delicate, abaxial surface and rachis glabrous or with sparse glandular hairs, adaxial surface glabrous. Pinna apex acuminate. Proximal pinnae 5--18 cm, ± perpendicular to rachis, with basiscopic pinnules ± perpendicular to costa; basal basiscopic pinnule sessile, pinnate-pinnatifid (with basal pinnulets, and sometimes 2 adjacent pinnulets, separate), basal basiscopic pinnulet usually longer (sometimes equaling or shorter) than adjacent pinnulet; 2d basal basiscopic pinnule sessile with basal basiscopic pinnulet usually longer than or equaling adjacent pinnulet; basal acroscopic pinnule sessile, with basal basiscopic pinnulet usually longer than or equaling adjacent pinnulet. Pinnae of 2d pair usually sessile with basal basiscopic pinnule longer than or equaling adjacent pinnule and markedly longer than basal acroscopic pinnule; basal acroscopic pinnule distinctly shorter than adjacent pinnule or rarely absent, apex often crenulate, obtuse. Pinnae of 3d pair usually sessile with basal basiscopic pinnule longer than or equaling adjacent pinnule and longer than basal acroscopic pinnule; basal acroscopic pinnule shorter than adjacent pinnule. Ultimate segments of proximal pinnae oblong, crenate to slightly lobed, apex crenulate, acute. Spores 27--31 µm. 2 n = 80.

Shaded, rocky slopes and ravines, mixed coniferous woods, moist stream and creek banks; of conservation concern; 0--2400 m; Alta., B.C.; Alaska, Idaho, Mont., Oreg., Wash., Wyo.; Asia in ne former Soviet republics.

In addition to the west coast of North America, Gymnocarpium disjunctum is found on Sakhalin Island in southern Kamchatka, in the former Soviet republics.