Stems 1--2 mm diam.; scales 2--4 mm. Fertile leaves usually 10--52 cm. Petiole 5--33 cm, with numerous glandular hairs distally; scales 2--6 mm. Blade broadly deltate, 2--3-pinnate-pinnatifid, 5--19 cm, usually firm and robust, abaxial surface moderately to densely glandular, rachis densely glandular, adaxial surface moderately glandular. Pinna apex acute. Proximal pinnae 3--13 cm, ± perpendicular to rachis, basiscopic pinnules ± perpendicular to costa; basal basiscopic pinnules either sessile or stalked, pinnate-pinnatifid or pinnatifid, if sessile then with basal basiscopic pinnulet usually shorter than adjacent pinnulet; 2d basal basiscopic pinnule sometimes stalked, if sessile then with basal basiscopic pinnulet shorter than or equaling adjacent pinnulet; basal acroscopic pinnule sometimes stalked, if sessile then with basal basiscopic pinnulet shorter than or equaling adjacent pinnulet. Pinnae of 2d pair usually stalked, if sessile then with basal basiscopic pinnule usually shorter than adjacent pinnule and equaling basal acroscopic pinnule; basal acroscopic pinnule shorter than adjacent pinnule, apex often entire, rounded. Pinnae of 3d pair usually sessile with basal basiscopic pinnule shorter than adjacent pinnule and equaling basal acroscopic pinnule; basal acroscopic pinnule equaling or shorter than adjacent pinnule. Ultimate segments of proximal pinnae oblong, entire to slightly crenate, apex entire, rounded. Spores 34--39 µm. 2 n = 160.
"Much like no. 1 [Gymnocarpium dryopteris (L.) Newman] ; blade green, densely and finely glandular (as also the petiole), a little narrower, deltoid, to 14 × 16 cm; segments of the basal pinnae ovate-oblong, obtuse, sessile, the lowest basal one mostly less than a fourth as long as the main rachis; ultimate segments to 9 mm, with entire to crenate, mostly recurved margins; 2n=160 (ours). On calcareous rocks; circumboreal, s. to Pa., Mich., Io., and Ida. (G. jessoense; Dryopteris r.; Phegopteris r.)"
|Limestone oak fern, gymnocarpe de robert|