Tennessee's Rarest Plant: Hart's-tongue Fern
**If you have ever wondered why “The Sinkhole” here in Marion County is closed for visitation, perhaps this will give you some insight on why some caves are closed.
Sept. 13, 1897
My Dear Madam,
The plant I want to know of is...hart's tongue fern...This fern is found only here in Central New York; two places in Canada; in Mexico somewhere; and "near South Pittsburgh, TN."...I attend Syracuse University, and this is my last year there. I am very anxious to get together a good deal of material on this fern, and shall anxiously await a reply from you...
Very sincerely yours,
Will R. Maxon
The author of this letter, who would later become curator of the U.S. National Herbarium and president of the American Fern Society, was writing Mrs. Joseph Lodge of South Pittsburg, Tennessee, about what might today be the rarest of Tennessee's plants. Our single known population of hart's-tongue fern (Asplenium scolopendrium var. americanum (Fern.) Kartesz & Gandhi) inhabits a sinkhole on the side of the Cumberland Plateau in Marion County.
First discovered in 1878 when the territory was being prospected for coal, the population decreased from approximately 200 plants to "only a few left" in 1925. In 1929, fearing the loss of the waning population, interested parties sprinkled spores from plants in Ontario, Canada, into the sinkhole. It is not known if succeeding plants were derived from the introduced spores or from the original stock.
Hart's-tongue's spotty distribution, as noted in the letter, is the result of its particular environmental requirements: constant low temperatures; plenty of shade and moisture; and rich, limestone-based soil. A boreal plant, it was forced southward during the ice ages, and our relict population has clung on in this deep sinkhole, as well as in two similar sites in Alabama.
George Ramseur, Director emeritus of the Sewanee Herbarium, began visiting the sinkhole in 1963 and has continued to chart the progress of the population. Since he began making his observations, there have been environmental changes due to trees dying or falling and altering the amount of light reaching the sinkhole floor. The nature of the sinkhole allows only a few hours per day of direct sunlight. The number of plants has fluctuated widely, with a maximum of 16 plants. In 1993, he found only one small plant, and for several years he did not see more than one plant on any visit. All of these plants were very small, with fronds less than two inches long, and none had reached maturity to a state of spore production.
In 1996, a visit by staff members of the Tennessee Nature Conservancy located two plants in the sinkhole's moss-and liverwort-covered ledges and sticky clay soil. In 1999, those plants had disappeared, and two different plants were located by a member of the National Speleological Society. These two plants appear to be in good condition. One has five or more leaves up to about four inches in length and the other has five leaves up to nearly two inches long. Tennessee's rarest plant is still here. It is, however, in need of protection.
