Stems 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. Leaves monomorphic, crowded near stem apex, to 45 cm, nearly all bearing sori. Petiole variable in color but mostly dark brown at base, gradually becoming straw-colored distally, shorter than blade, sparsely scaly at base. Blade 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. Pinnae 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. Veins directed into teeth and notches. Indusia cup-shaped, apex truncate, with scattered, unicellular, gland-tipped hairs. Spores spiny, usually 38--42 µm. 2 n = 168. Sporulating summer--fall. Cracks and ledges on cliffs, rarely terrestrial; often on calcareous substrates or associated with man-made habitats such as rock walls or bridge abutments; 100--500 m; Ala., Ark., Ga., Ill., Ind., Iowa, Kans., Ky., Md., Mo., N.C., Ohio., Okla., Pa., Tenn., Va., W.Va., Wis. 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 .
Perennial fern 10 - 45 cm tall Leaves: clustered, stalked, green, delicate, thin, deciduous (dying back in winter), 5 - 40 cm long, widest at or near base, in outline broadly to narrowly triangular with abruptly-tapered tip, but pinnately compound. The main "midrib" (rachis) occasionally has some single-celled, gland-tipped hairs, and sometimes also some misshapen bulblets. Rhizome: short, compact but creeping, internodes short, hairless, but with tan to light brown lance-shaped scales, and covered with numerous remnant leaf stalk bases. Leaf stalks: clustered at tip of rhizome, usually dark brown at base, gradually becoming straw-colored, shorter than leaf blade, and sparsely scaly at base. Spores: 64 per sac, brownish, all of one kind, single-sectioned (monolete), usually 38 - 42 microns long, oblong or kidney-shaped, and spiny. Produced on nearly all the leaves, the spores give rise to the gametophyte (the sexual phase of the plant), which is small, green, heart-shaped, hairless or often with glands or hairs, and sits above the ground.
Similar species: Since it can occasionally have bulblets along the rachises or costae Cystopteris tennesseensis is probably most similar to C. bulbifera, but that species will have a much more dense covering of gland-tipped hairs along the rachises, costae, segment midribs, and spore-cluster coverings (indusia); the leaf blades are almost always widest at the base and have a gradually long-tapering tip; only the leaves in the summer and fall produce spore-sac clusters (sori); the leaf stalks are reddish when young; and the spores are usually smaller, only 33 - 38 microns. The other three species of Cystopteris in the Chicago Region, C. fragilis, C. protrusa and C. tenuis, differ by not having glandular hairs on any of the leaf portions, the leaf blades are elliptic to lance-shaped and usually widest at the middle or just below the middle, and the rachises and costae never have bulblets.
Habitat and ecology: Not common, in limestone canyons and along limestone cliffs.
Occurence in the Chicago region: native
Notes: This species is actually an allotetraploid species derived from hybridization between C. bulbifera and C. protrusa. In many ways it appears intermediate between both parents in general morphology. For further information one should see the Flora of North America (1993) treatment and references cited there.
Etymology: Cystopteris comes from the Greek words cystis, meaning bladder, and pteris, meaning fern. Tennesseensis means "of, or from Tennessee".