Cystopteris tenuis
Cystopteris tennesseensis
cystoptère ténue, Mackay's brittle fern, Mackay's fragile fern, upland brittle bladderfern
Tennessee bladder 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 short, heavily beset with old petiole bases, hairs absent;
scales usually tan to light brown, lanceolate, radial walls tan to brown, thin, luminae tan.
monomorphic, clustered at stem apex, to 40 cm, nearly all bearing sori.
monomorphic, crowded near stem apex, to 45 cm, nearly all bearing sori.
dark at base, mostly green to straw-colored distally, shorter than or nearly equaling blade, base sparsely scaly.
variable in color but mostly dark brown at base, gradually becoming straw-colored distally, shorter than blade, sparsely scaly at base.
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.
deltate to narrowly deltate, 2-pinnate-pinnatifid, usually widest at or near base, apex short-attenuate;
rachis and costae with occasional unicellular, gland-tipped hairs, with or without bulblets (usually misshapen);
axils of pinnae with infrequent 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 serrate;
proximal pinnae pinnatifid to pinnate-pinnatifid, ± equilateral, basiscopic pinnules not enlarged, basal basiscopic pinnules sessile to short-stalked, base truncate to obtuse;
distal pinnae ovate to oblong.
directed into teeth and notches.
directed into teeth and notches.
ovate to cup-shaped, without gland-tipped hairs.
cup-shaped, apex truncate, with scattered, unicellular, gland-tipped hairs.
spiny, usually 39–50 µm. 2n = 168.
spiny, usually 38–42 µm. 2n = 168.
Cystopteris tenuis
Cystopteris tennesseensis
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 tennesseensis, an allotetraploid species, has C. bulbifera and C. protrusa as diploid progenitors. The relative distinctiveness of these diploids suggests that identification of C. tennesseensis individuals should be straightforward. As with other members of Cystopteris, however, a series of features makes reliable recognition of this tetraploid challenging. For some characteristics (occasional unicellular, gland-tipped hairs and bulblets; short-attenuate, narrowly deltate blades), it is intermediate between its parents; for others (very short internodes and crowded leaves; occurrence on rock), it tends toward C. bulbifera. This unequal intermediacy, the multiple origins from genetically different individuals (C. H. Haufler et al. 1990), and the occurrence of sterile backcross triploids with its diploid progenitors in zones of sympatry has blurred the already subtle features distinguishing this allopolyploid. For example, some individuals of C. bulbifera may have very few glandular hairs, and some C. tennesseensis appear to lack glandular hairs entirely (R. F. Blasdell 1963). Further, sterile tetraploid hybrids (called C. × wagneri R. C. Moran) between C. tennesseensis and C. tenuis have been reported (R. C. Moran 1983) and verified through isozyme analyses (C. H. Haufler, unpubl. data). Finally, as discussed above, the recently recognized C. utahensis (C. H. Haufler and M. D. Windham 1991) is extremely similar morphologically to C. tennesseensis.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
- Local Web sites:
CalFlora, CalPhotos, 
Go Botany, 
IL Wildflowers, 
KS Wildflowers, 
MD Biodiversity, 
MI Flora, 
MN Wildflowers, 
MO Plants 
WildflowerSearch
iNaturalist (observations)
USDA Plants Database- LBJ Wildflower Center
- SEINet
- Plants of the World Online
- Encyclopedia of Life
- Wikipedia
- Google Image Search
