Cystopteris tenuis
Cystopteris montana
cystoptère ténue, Mackay's brittle fern, Mackay's fragile fern, upland brittle bladderfern
cystoptère des montagnes, mountain bladder fern, mountain brittle fern
creeping, not cordlike, internodes short, beset with old petiole bases, hairs absent;
scales tan to light brown, lanceolate, radial walls thin, luminae tan.
long-creeping, cordlike, internodes 1–2(–4) cm, old petiole bases few, hairs absent;
scales usually tan to light brown, ovate-lanceolate, radial walls tan to brown, thin, luminae tan.
monomorphic, clustered at stem apex, to 40 cm, nearly all bearing sori.
monomorphic, at stem apex but not tightly clustered, to 45 cm, sori production about equal on all leaves (fairly independent of season).
dark at base, mostly green to straw-colored distally, shorter than or nearly equaling blade, base sparsely scaly.
dark brown to black at base, gradually becoming green or straw-colored distally, (1–)2–3 times length of blades, sparsely scaly throughout.
lanceolate to narrowly elliptic, 1(–2)-pinnate-pinnatifid, widest at or just below middle, apex short-attenuate;
rachis and costae lacking gland-tipped hairs or bulblets;
axils of pinnae lacking multicellular, gland-tipped hairs.
elongate-pentagonal, 3(–4)-pinnate-pinnatifid;
rachis and costae lacking gland-tipped hairs or bulblets;
axils of pinnae with occasional multicellular gland-tipped hairs.
typically at acute angle to rachis, often curving toward blade apex, margins crenulate;
proximal pinnae pinnatifid to pinnate-pinnatifid, ± equilateral, basiscopic pinnules not enlarged;
basal basiscopic pinnules sessile, base cuneate to obtuse, distal pinnae ovate to narrowly elliptic.
ascending, typically at acute angle to rachis, only proximal pinnae occasionally curving toward blade apex, margins serrate;
proximal pinnae pinnate-pinnatifid, inequilateral, basal basiscopic pinnule stalked, enlarged, base truncate to obtuse;
distal pinnae deltate to ovate.
directed into teeth and notches.
directed into notches.
ovate to cup-shaped, without gland-tipped hairs.
cup-shaped, apex truncate, hairs gland-tipped only along margin.
spiny, usually 39–50 µm. 2n = 168.
spiny, usually 37–42 µm. 2n = 168.
Cystopteris tenuis
Cystopteris montana
Long recognized as Cystopteris fragilis var. mackayi, C. tenuis was returned to species status by R. C. Moran (1983b). It is probably an allotetraploid originating from C. protrusa and an extinct diploid related to C. fragilis (C. H. Haufler 1985; C. H. Haufler and M. D. Windham 1991).
Cystopteris tenuis is common in eastern North America and less frequent at the northern and western perimeter of its range. In the center of its distribution (Minnesota, Iowa, Illinois, Wisconsin, Indiana, Ohio, Pennsylvania), the narrow, elliptic pinnae angled toward the blade apex and the rounded teeth make C. tenuis relatively distinct from C. fragilis and C. protrusa (although the early season, sterile leaves of C. protrusa often resemble those of C. tenuis). In the west and especially in the northeast, C. tenuis and C. fragilis are difficult to distinguish. For the most part, C. fragilis is confined to higher latitudes and elevations than C. tenuis, but the two species can be sympatric and occasionally form sterile tetraploid hybrids. Cystopteris protrusa and C. tenuis are infrequently sympatric, but where they are, sterile triploid hybrids can occur. Hybrids between C. tenuis and C. tennesseensis are recognized as C. × wagneri (R. C. Moran 1983). Hybridization between C. tenuis and C. bulbifera has also been reported (R. C. Moran 1982b). This hybrid, C. × illinoensis R. C. Moran, is known only from the type and needs to be studied further.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Cystopteris montana, the most distinctive of the Cystopteris in the flora, probably is allied to Asian species. Although this boreal species is restricted primarily to high latitudes, it occurs disjunctly at high elevations in Colorado, where its habitats are being threatened by development. Cystopteris montana does not hybridize with any other Cystopteris in the flora, but it has been implicated in the origin of the European allopolyploid C. alpina (Roth) Desvaux.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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