Cystopteris tenuis
Cystopteris reevesiana
cystoptère ténue, Mackay's brittle fern, Mackay's fragile fern, upland brittle bladderfern
Reeves' bladderfern, Southwestern 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.
creeping, not cordlike, internodes usually long, with scattered persistent petiole bases, hairs absent;
scales tan to brown, ovate to lanceolate, radial walls thin, luminae tan.
monomorphic, clustered at stem apex, to 40 cm, nearly all bearing sori.
monomorphic, clustered at stem apex, to 45 cm, bearing sori throughout year.
dark at base, mostly green to straw-colored distally, shorter than or nearly equaling blade, base sparsely scaly.
highly variable in color, from uniformly dark purple to uniformly straw-colored, but mostly dark purple at base, grading to straw-colored at junction with blade, shorter than blade, base sparsely scaly.
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.
ovate to elliptic, 2–3-pinnate, widest at or just below middle, apex short-attenuate;
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.
usually perpendicular to rachis, not curving toward blade apex, margins dentate to crenate;
proximal pinnae pinnate-pinnatifid to 2-pinnate, ± equilateral, basiscopic pinnules not enlarged;
basal basiscopic pinnules mostly short-stalked, base truncate to obtuse, distal pinnae deltate to ovate.
directed into teeth and notches.
directed into teeth and notches.
ovate to cup-shaped, without gland-tipped hairs.
cup-shaped to lanceolate, gland-tipped hairs absent.
spiny, usually 39–50 µm. 2n = 168.
spiny, usually averaging 33–41 µm. 2n = 84.
Cystopteris tenuis
Cystopteris reevesiana
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.)
The finely dissected leaves, dark petioles, creeping stems, smaller spores, and terrestrial habit distinguish Cystopteris reevesiana from C. fragilis in the southwest. On rock and at high elevations, however, C. reevesiana can have stems with short internodes and leaves that are reduced in size and dissection (resembling C. fragilis). In southern Colorado, the two species are sympatric in some areas and form triploid hybrids. Cystopteris reevesiana and C. bulbifera are the diploid progenitors of C. utahensis, which occasionally crosses with C. reevesiana to produce sterile triploid hybrids of intermediate morphology.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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