Cystopteris laurentiana |
Cystopteris fragilis |
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cystoptère laurentienne, Laurentian bladder fern, Laurentian fragile fern, St. Lawrence bladderfern |
bladder fern, brittle bladderfern, brittle fern, cystoptère fragile, fragile brittle fern, fragile fern |
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Stems | creeping, not cordlike, internodes very short, less than 5 mm, heavily beset with old petiole bases, hairs absent; scales uniformly brown to ± clathrate, radial walls brown, luminae clear. |
creeping, not cordlike, internodes short, beset with old petiole bases, hairs absent; scales tan to light brown, lanceolate, radial walls thin, luminae tan. |
Leaves | monomorphic, clustered at stem apex, to 45 cm, nearly all bearing sori. |
monomorphic, clustered at stem apex, to 40 cm, nearly all bearing sori. |
Petiole | usually dark at base, grading to straw-colored distally, shorter than blade, sparsely scaly at base. |
dark at base, mostly green to straw-colored distally, shorter than or nearly equaling blade, base sparsely scaly. |
Blade | ovate to narrowly ovate, 2-pinnate to 2-pinnate-pinnatifid, widest above base, apex short-attenuate; rachis and costae usually sparsely invested with unicellular, gland-tipped hairs, occasionally with misshapen bulblets; axils of pinnae with occasional multicellular, gland-tipped hairs. |
lanceolate to narrowly elliptic, 1(–2)-pinnate-pinnatifid, widest at or just below middle, apex acute; rachis and costae lacking gland-tipped hairs or bulblets; axils of pinnae lacking multicellular, gland-tipped hairs. |
Pinnae | typically perpendicular to rachis, not curving toward blade apex, margins serrate; proximal pinnae pinnate-pinnatifid to pinnatifid, ± equilateral, basiscopic pinnules not enlarged, basal basiscopic pinnules sessile to short-stalked, base truncate to obtuse; distal pinnae ovate to oblong. |
usually perpendicular to rachis, not curving toward blade apex, margins serrate to sharply dentate; proximal pinnae pinnatifid to pinnate-pinnatifid, ± equilateral, basiscopic pinnules not enlarged; basal basiscopic pinnules sessile, base truncate to obtuse, distal pinnae deltate to ovate. |
Veins | directed into teeth and notches. |
directed mostly into teeth. |
Indusia | cup-shaped, apex truncate, typically sparsely invested with unicellular, gland-tipped hairs. |
ovate to lanceolate, without gland-tipped hairs. |
Spores | spiny, usually 49–60 µm. 2n = 252. |
spiny or verrucate, usually 39–60 µm. 2n = 168, 252. |
Cystopteris laurentiana |
Cystopteris fragilis |
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Phenology | Sporulating summer–fall. | Sporulating summer–fall. |
Habitat | Cracks and ledges on cliffs, often on calcareous substrates | Mostly on cliff faces, also in thin soil over rock |
Elevation | 0–1000 m (0–3300 ft) | 0–4500 m (0–14800 ft) |
Distribution |
CT; IA; IL; MA; MI; MN; PA; VT; WI; NB; NF; NS; ON; QC
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AK; CA; CO; CT; IA; ID; IL; IN; KS; MA; ME; MI; MN; MT; ND; NE; NH; NM; NV; NY; OH; OR; PA; SD; TX; UT; VT; WA; WI; WY; AB; BC; MB; NB; NF; NS; NT; ON; PE; QC; SK; YT; SPM; Greenland; worldwide
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Discussion | Cystopteris laurentiana is a sexual allohexaploid species with C. bulbifera as the diploid parent and C. fragilis as the tetraploid. Cystopteris laurentiana was previously thought to be common only in the Great Lakes region (R. F. Blasdell 1963); it is now known to occur frequently in the Driftless Area of the Midwest. Because C. laurentiana can be difficult to distinguish from C. fragilis, specimens with ovate leaves having unusually large spores and growing on moist cliffs should be checked carefully for occasional glandular hairs, the distinguishing feature of C. laurentiana. Sterile pentaploid hybrids between C. laurentiana and C. fragilis have been discovered where the two species are sympatric. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Cystopteris fragilis is most often confused with C. tenuis in the east and C. reevesiana in the southwest. Habitat and geography, as well as the morphologic features discussed in the key, usually serve to separate these taxa. For instance, C. fragilis is more likely to be found on cliffs whereas the other species prefer boulders and soil (C. fragilis occurs at higher elevations and/or latitudes than the other species). These distinctions can be confounded when C. fragilis forms hybrids with sympatric species. Sterile pentaploid plants have been discovered where C. fragilis overlaps with C. laurentiana, tetraploid hybrids are likely where C. fragilis occurs with C. tenuis, and triploids may form where C. fragilis is found with C. reevesiana. Even after segregating relatively distinct elements such as Cystopteris protrusa, C. reevesiana, and C. tenuis, and identifying sterile hybrids, C. fragilis still remains a polymorphic and complex taxon that probably contains a number of natural, cryptic evolutionary units. For example, morphologically distinct hexaploid cytotypes have been reported (C. H. Haufler and M. D. Windham 1991). These occur as isolated and 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. The presence of verrucate spores (as opposed to the normal spiny spores) has been used to circumscribe Cystopteris dickieana. Although genetic analyses have not been undertaken, we think the verrucate spore is probably a recessive feature controlled by one or 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. Perhaps in this region the genetic combinations specifying verrucate spores have been fixed. Following R. F. Blasdell (1963), C. dickieana is also considered here to be conspecific with C. fragilis because (1) early stages in the development of spiny spores can appear verrucate (A. C. Jermy and L. Harper 1971), (2) the hexaploid cytotypes discussed above always have verrucate spores, regardless of their parentage, (3) individuals with verrucate spores can be found in populations that are otherwise uniformly spiny-spored, and (4) individuals and populations that have verrucate spores are not otherwise (morphologically, ecologically, or genetically) distinct from those that have spiny spores. Especially in the western portion of its North American range (British Columbia, Washington, Montana, Idaho, Oregon, California), Cystopteris fragilis appears to be developing morphologically and ecologically distinctive variants. Hybrid individuals with aborted spores have been discovered, and plants from these areas increasingly tend to grow on both soil and rock and to have slightly different morphologies on the two substrates. These variants intergrade, however, and are not sufficiently distinct to warrant species status. This polymorphic polyploid is probably actively speciating at the tetraploid level, perhaps through gene silencing (C. R. Werth and M. D. Windham 1991). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 2. | FNA vol. 2. |
Parent taxa | Dryopteridaceae > Cystopteris | Dryopteridaceae > Cystopteris |
Sibling taxa | ||
Synonyms | C. fragilis var. laurentiana | Polypodium fragile, C. dickieana, C. fragilis subsp. dickieana |
Name authority | (Weatherby) Blasdell: Mem. Torrey Bot. Club 21(4): 51. (1963) | (Linnaeus) Bernhardi: Neues J. Bot. 1(2): 27, plate 2, fig. 9. (1805) |
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