Gymnocarpium dryopteris (L.) Newman (redirected from: Thelypteris dryopteris)
Family: Thelypteridaceae
western oakfern,  more...
[Dryopteris dryopteris (L.) Britt.,  more]
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Stems 0.5--1.5 mm diam.; scales 1--4 mm. Fertile leaves usually 12--42 cm. Petiole 9--28 cm, with sparse glandular hairs distally; scales 2--6 mm. Blade broadly deltate, 2-pinnate-pinnatifid, 3--14 cm, lax and delicate, abaxial surface and rachis glabrous or with sparse glandular hairs, adaxial surface glabrous. Pinna apex entire, rounded. Proximal pinnae 2--12 cm, ± perpendicular to rachis, with basiscopic pinnules ± perpendicular to costa; basal basiscopic pinnule usually sessile, pinnatifid or rarely pinnate-pinnatifid, if sessile then with basal basiscopic pinnulet often equaling or longer than adjacent pinnulet; 2d basal basiscopic pinnule sessile, with basal basiscopic pinnulet equaling or longer than adjacent pinnulet; basal acroscopic pinnule sessile, with basal basiscopic pinnulet longer than or equaling adjacent pinnulet. Pinnae of 2d pair usually sessile with basal basiscopic pinnule longer than or equaling adjacent pinnule and about equal to basal acroscopic pinnule; basal acroscopic pinnule equaling or slightly shorter than adjacent pinnule, often with entire, rounded apex. Pinnae of 3d pair sessile with basal basiscopic pinnule equaling adjacent pinnule and equaling basal acroscopic pinnules; basal acroscopic pinnule equaling or slightly shorter than adjacent pinnule. Ultimate segments of proximal pinnae oblong, entire to crenate, apex entire, rounded. Spores 34--39 µm. 2 n = 160. Cool, coniferous and mixed woods and at base of shale talus slopes; 0--3000 m; Greenland; St. Pierre and Miquelon; Alta., B.C., Man., N.B., Nfld., N.W.T., N.S., Ont., P.E.I., Que., Sask., Yukon; Alaska, Ariz., Colo., Conn., Idaho, Iowa, Maine, Mass., Mich., Minn., Mont., N.H., N.J., N.Mex., N.Y., Ohio, Oreg., Pa., R.I., S.Dak., Vt., Wash., W.Va., Wis., Wyo.; n,c Europe; n Asia to China, Japan. Gymnocarpium dryopteris is a fertile allotetraploid species that arose following hybridization between G . appalachianum and G . disjunctum (see reticulogram). Its wide distribution over much of the north temperate zone has provided ample opportunity for secondary contact between G . dryopteris and each of its diploid parents, thereby resulting in a wide-ranging composite of abortive-spored triploid crosses ( G . disjunctum × G . dryopteris and G . appalachianum × G . dryopteris ). These relationships are shown on the diagram. Sterile triploid plants are not restricted only to areas where the range of the tetraploid overlaps with that of either diploid. Their broad distribution could be explained in part by their spores, which are of two types: malformed, black, and with very exaggerated perispores, or round with extensive netted perispores (K. M. Pryer and D. M. Britton 1983). The latter spore type is capable of germination and presumably permits the plants to reproduce apogamously. The name G . × brittonianum (Sarvela) Pryer & Haufler has been applied to the G . disjunctum × G . dryopteris hybrid formula (K. M. Pryer and C. H. Haufler 1993). The type of G . × brittonianum has aborted and round spores, and leaves that strongly resemble those of G . disjunctum . They are large, 3-pinnate-pinnatifid, and the second and third pairs of pinnae are sessile with basal basiscopic pinnules markedly longer than the basal acroscopic pinnules. Sterile triploid plants with a morphology similar to the type of G . × brittonianum are frequent. The biology of both of these cryptic hybrid taxa needs further study, which should lead to detailed morphologic descriptions and distribution maps. Gymnocarpium dryopteris also hybridizes with both G . jessoense subsp. parvulum and G . robertianum .

Perennial fern 10 - 45 cm tall Leaves: spaced, not densely clumped, stalked, yellow-green, delicate, deciduous, 3 - 14 cm long, up to 25 cm wide, broadly triangular in outline, but divided into three sections, which are further divided. The leaves are usually hairless, though they can be sparsely glandular-hairy along the underside of the main "midrib" (rachis) Rhizome: long-creeping, very slender (0.5 - 1.5 mm diameter), with 1 - 4 mm long scales. Leaf stalks: not clumped, 10 - 30 cm long, sparsely glandular-hairy in upper half, and with 2 - 6 mm long scales at base. Spores: 64 per sac, brownish, all of one kind, single-sectioned (monolete), oblong or kidney-shaped, and wrinkled. The spores give rise to the gametophyte (the sexual phase of the plant), which is small, green, heart-shaped, hairless or often with glands or hairs, and sits above the ground.

Similar species: Gymnocarpium dryopteris is probably most easily confused with species of Dryopteris and Cystopteris, but both of those genera have a specialized flap of tissue (indusium) that cover the clusters of spore sacs. Without fertile fronds, it can be very difficult to distinguish this species from other ferns, but in the Chicago Region this is about the only small, delicate, broadly triangular-leaved fern that has three, triangular, main divisions that are further pinnately divided. In general form, this species almost appears to be a miniature, more delicate version of the bracken fern, Pteridium aquilinum var. latiusculum.

Habitat and ecology: Incredibly rare, in cool, coniferous and mixed woods, usually much to the north of the Chicago Region.

Occurence in the Chicago region: native

Notes: This species has erroneously been called Dryopteris disjuncta, which really is a synonym of the Pacific Northwestern species Gymnocarpium disjunctum. The single reporting of G. dryopteris in Racine County, Wisconsin by Tryon et al. (1940) may not have a vouchered herbarium specimen associated with it. We cannot find one at the Wisconsin State Herbarium, but it is possible it was provided to a different herbarium. This species arose from hybridization of G. appalachianum and G. disjunctum. The majority of this fern's range is further north of the Chicago Region, but three Illinois counties along the Wisconsin border to the west of the Chicago Region do have populations of this fern. It is still rare in those counties, and the species is listed as Endangered in the state of Illinois.

Author: The Field Museum

Petiole 10-30 cm; blade yellow-green, scaleless, deltoid-pentagonal, to 18 נ25 cm, bipinnate-pinnatifid to tripinnate-pinnatifid, glabrous or occasionally slightly glandular especially along the rachis, pinnae several pairs, opposite, the members of the lowest pair deltoid and each nearly as long as the rest of the blade, with a petiolule to 2.5 cm long, distinctly asymmetrical, the lowest basiscopic segment evidently the largest, mostly a third as long as the main rachis or longer; ultimate segments oblong, 8-18 mm, obtuse, the margins crenate to subpinnatifid, not recurved; veins 2-6 pairs, mostly simple; 2n=160 (ours). Cool woods and talus-slopes; circumboreal, s. to Va., N.C., O., Ill., Io., and Ariz. A vegetatively reproducing hybrid with the next is G. بeterosporum W. H. Wagner.

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

©The New York Botanical Garden. All rights reserved. Used by permission.
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