American Hart's-tongue Fern

Asplenium scolopendrium var. americanum

Description

American hart's-tongue fern, Asplenium scolopendrium var. americanum, has evergreen, strap-shaped fronds, growing up to 17 in (42 cm) long. Fronds, which have lobed (auriculate) bases, arise in clusters from an underground rhizome. Petioles (leaf stalks) are covered with cinnamon-colored scales.

Habitat

This rare fern species is typically found in close association with outcrops of dolomitic limestone in soils that are high in magnesium. It requires cool temperatures, high humidity, moist soil, and the deep shade provided by a mature forest canopy or overhanging rock cliffs. In the southern portion of its range, where the climate would otherwise be too warm, it is found only in pit cave entrances, which are relatively cool and shaded.

Distribution

American hart's-tongue fern is found in small, very isolated populations in a range that extends from southern Ontario, Canada, south from the Great Lakes region to northern Alabama. This disjunct pattern of distribution implies that the fern was once more abundant under the cooler climatic conditions that prevailed at the end of the last major glaciation.

Populations of this fern are known to exist in 21 locations in the United States—two in Alabama, one in Tennessee, six in Michigan, and 12 in New York. The species also grows in southern Ontario, Canada. It is most abundant in Canada, which supports the bulk of the known world population.

The Alabama populations are situated in Jackson and Morgan counties, both located in limestone sinkholes. The Jackson County site is managed as a satellite of the Wheeler National Wildlife Refuge, but the population there had dwindled by 1990 to four (in 1979, 20 plants had been observed at that site). The Morgan County population is healthier, but its numbers saw a similar decline over the same period, dropping from some 97 plants in 1981 to only 39 plants in 1990. That population is on privately owned land.

The single Tennessee population, in Marion County, Tennessee, on land leased by The Nature Conservancy, originally supported 200 plants, but by 1980, the site supported only 17 plants, and by 1991, the plant was nearly extirpated altogether, with only one or two individuals surviving.

Four populations, comprising fewer than 500 plants, are recognized by the Michigan Natural Features Inventory in that state, all in Mackinac County. Two population sites are owned by the Michigan Nature Association and have been described as healthy and vigorous. One population falls within the Hiawatha National Forest and is managed by the Forest Service. The fourth population is on privately owned land and currently receives no protection.

The New York Natural Heritage Program identifies nine populations in that state, all within a limited area of Madison and Onondago counties. One Madison County population of about 350 plants is found within a state park, while two others, totaling fewer than 100 plants, occur on private property. Two large populations, with a combined total of more than 2,500 plants, occur within a state park in Onondago County. Four smaller populations are found on private land nearby and are considered extremely vulnerable. Several historically known populations from this county were lost in the 1930s, primarily to quarrying.

Several vigorous and healthy Canadian populations are found in Bruce County, Ontario, while the four neighboring counties (Peel, Halton, Dufferin, and Simcoe) support smaller, peripheral colonies. Although abundant in Ontario when compared with U.S. populations, hart's-tongue fern remains an extremely rare plant in Canada.

Threats

Because of its occurrence in restricted localities in the United States and its minimal numbers, American hart's-tongue fern is threatened by any number of actions that disturb or alter its specialized habitat. Plants have been lost due to logging, quarrying, residential development, and recreational pursuits (hikers who leave trails and stumble into the habitat have accidentally trampled the plant). Canadian populations also are threatened by lumbering and quarrying, and by development of land for ski resorts or for country estates.

Insect infestations are another natural danger to the plant. A 1985 infestation of leaf miners destroyed the leaves on the trees above one of the Michigan population sites. The resulting loss of shade desiccated many of the ferns growing on the forest floor. Such insect infestations, which temporarily remove the leaves of the canopy or result in long-term damage to the trees found there, remain a potential threat to the species.

Conservation and Recovery

The 1993 recovery plan for the American hart's-tongue fern states that the recovery goal is delisting, which will be considered when there are at least 15 self-sustaining populations in the United States that are protected to such a degree that the species no longer qualifies for protection under the Endangered Species Act. The plan calls for a number of actions, including the protection of known populations; the completion of needed biological studies; and the implementation of habitat management (if needed); the protection of genetic material and the re-establishment of populations (if necessary). The plan also calls for enforcement as well as the development of educational programs and the monitoring of the recovery process. The plan projected a recovery date of 1999, assuming the availability of funds for needed recovery activities.

Contacts

U. S. Fish and Wildlife Service
Regional Office of Endangered Species
Federal Building
Ft. Snelling
Twin Cities, Minnesota 55111
http://midwest.fws.gov/

U. S. Fish and Wildlife Service
Regional Office of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
http://southeast.fws.gov/

U. S. Fish and Wildlife Service
Regional Office of Endangered Species
300 Westgate Center Dr.
Hadley, Massachusetts 01035
http://northeast.fws.gov/

References

Cinquemani, D. M., et al. 1988. "Periodic Censuses of Phyllitis scolopendrium var. americana in Central New York State." American Fern Journal 78(2):37-43.

Lellinger, D. B. 1985. A Field Manual of the Ferns and Fern-Allies of the United States and Canada. Smithsonian Institution Press, Washington, D.C.

U.S. Fish and Wildlife Service. 1993. "American Hart's-tongue Fern Recovery Plan." U.S. Fish and Wildlife Service. Washington, D.C.