Cystopteris fragilis (L.) Bernh.
Brittle fern, fragile fern, cystopté fragile.
Polypodiaceae, fern family.
Neues J. Bot. 1(2): 26, plate 2 fig. 9. 1806 [1805].
Polypodium fragile L. Sp. Pl. 2: 1091. 1753.
Cystopteris dickieana Sim
Cystopteris fragilis subsp. dickieana (Sim) Hylander
Cystopteris fragilis var. woodsioides Christ
Filix fragilis (L.) Underwood
Plants with creeping unbranched stems in loose clusters; less than 15 cm high, or more than 15 cm high; (3–)10–25 cm high. Roots red-brown, or black (or dark brown). Ground-level or under-ground stems horizontal (covered with mainly erect, old petiole bases); stoloniferous; compact; 2–20 mm wide (often a confused clump-like stem portion). Leaves mostly basal (arising along the horizontal stem); alternate; compound. Petioles 15–160(–200) mm long; glabrous (glabrescent), or scaly (with sparse scales at the base, these tan to light brown, lanceolate, 0.2–0.4 mm wide; petioles dark at the base but mostly green to straw-coloured, shorter than, or nearly equalling, the blade, without articulate petioles). Blades 10–150 mm long; 5–35(–50) mm wide (CAN 204410); herbaceous; circinate when young (narrowly elliptic or lanceolate fronds); with pinnate veins; adaxial surface glabrous. Blades abaxial surface glabrous. Leaf margins serrate. Plants reproducing by spores borne in sporangia. Sori with a distinct indusium. Indusia ovate, whitish, lanceolate scales that fall early (see image library).
Chromosome information. 2n = 168 and 252.
Distribution. Circumpolar. Arctic, or alpine. Range in the Canadian Arctic Archipelago widespread. Greenland, St. Pierre and Miquelon, Canada, United States, Eurasia. Arctic Islands: Baffin, Devon, Ellesmere, Axel Heiberg, Victoria, Somerset, Coats.
Ecology and habitat. Recorded from calcareous ridges with good drainage, rock ledges at the base of cliffs, a calcareous gravel beach, (CAN 258542), a limestone gravel beach, dry rocky slopes, (CAN 127415), alpine scree, moist rock crevices on a sunny cliff, and a moist habitat with accumulated soil, (CAN 518068).
Notes. Cystopteris fragilis occurs at higher latitudes and/or elevations than other species of Cystopteris. It is a polymorphic complex and morphologically distinct hexaploid cytotypes have been reported from disjunct populations in Ontario, Alaska, Arizona, Colorado, Montana, and Wyoming. Isozymic profiles of each of these populations indicate that the hexaploids are polyphyletic and should not be accorded species status (Haufler et al. 1993).
The presence of verrucate spores (as opposed to the normal spiny spores) has been used to circumscribe Cystopteris dickieana. It is possible that the verrucate spore is a recessive feature controlled by one, or only a few, genes. While present at low frequency in much of the range of C. fragilis, verrucate spores are particularly prominent in the Great Plains and some specimens from the Arctic have been assigned to C. dickieana, although there is no agreement on such assignments.
This polymorphic polyploid is probably actively speciating at the tetraploid level, perhaps through gene silencing (C.R. Werth and M.D. Windham 1991).
Illustrations. • Plant in habitat. Small fern plants growing on a turfy slope, under the shelter of a rock, near the sea, Nunavut, Baffin Island, Iqaluit, Apex area. July 27, 1982, J.M.Gillett 19077. • Plant in habitat. Isolated plant growing in the shelter of rocks. CMN Photo Library image S84–5601. • Plant in habitat. Plants growing among rocks at Cape Thompson, Alaska. CMN Photo Library S78–722. Photograph by Mildred and Raymond D. Wood. • Ground-level stems. Tiny high arctic plants with well developed stems covered with leaf bases that have broken at articulated joints. A, stem horizontal. B. stem tending to vertical. The specimen has produced four new leaves this growing season. Judging by the leaf bases, guestimate the age of the plant. Specimen collected Nunavut, Ellesmere Island, Lake Hazen. CAN 483324. • Leaf with young sori. A. Under surface of leaf pinnae showing each sorus covered with a whitish, scale-like indusium that falls early. B, upper surface of the leaf pinnae. The leaf veins are not very visible, but the position of the underlying sori can be seen. Specimen from Nunavut, Baffin Island, Nnettilling Lake, Burwash Bay. CAN 518068. • Leaf with old sori. A. Under surface of leaf pinnae showing sori from which the indusium has been lost, brown hairs and pale yellow brown sporangia. B. Unopened pale yellow sporangia and hairs among the sporangia. Specimen from Nunavut, Baffin Island, Iqaluit. CAN 518075. • Arctic Island Distribution.
Cite this publication as: S.G. Aiken, M.C. LeBlanc, and M.J. Dallwitz 2000 onwards. Pteridophytes of the Canadian Arctic Archipelago: Descriptions, Illustrations, Identification, and Information Retrieval.’ Version: 23rd February 2001. http://www.mun.ca/biology/delta/arcticf/’. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993, 1995, 2000) , and Aiken, Dallwitz et al. (1999) should also be cited (see References).
