Discovery of New Hart's Tongue Fern Population

Hart's tongue fern.
Hart's tongue fern (Asplenium scolopendrium var. americanum) grows only on shaded moss-covered rock. Photo by Sara Huebner.

Sori on the back of the Hart's tongue fronds.
Linear sori on the back of the Hart's tongue fronds produce spores. Photo by Sara Huebner.

Mark Jaunzems pointing to Hart's Tongue Fern.
Mark Jaunzems pointing to Hart's Tongue Fern. Notice the cracks in the bedrock. Photo by Sara Huebner.

Walking fern.
Walking fern (Asplenium rhizophyllum) is an associate of Hart's tongue fern also occurring on boulders. It differs by having long tapering tips. Photo by Sara Huebner.

A new population of American Hart's tongue fern (Asplenium scolopendrium var. americanum) was recently discovered on the east side of the Hiawatha National Forest in northern Michigan. Nationally, this fern is very rare. In North America, Hart's-tongue fern is locally abundant only on the Bruce Peninsula of Ontario. Isolated colonies occur in Alabama, New York, Tennessee, and northern Michigan. Hart's tongue fern is currently known in Michigan from eastern Mackinac and Chippewa Counties only. Up until now, there were six known locations of this federally threatened fern on the Hiawatha National Forest; the last of which was discovered in 1997.

Hart's tongue fern occurs on limestone and dolomite outcroppings of the Niagara Escarpment geologic formation. The Niagara Escarpment is a unique arc-shaped landform composed of a series of ridges and outcrops extending from eastern New York, through Ontario, the Upper Peninsula of Michigan, and into Door County of eastern Wisconsin. The shaded boulders and ledges that the ferns grow on are moist and typically covered in mosses and liverworts. Often the ferns occur in crevices of the limestone bedrock, known as “grykes”. The forest type is typically rich northern hardwoods, dominated by sugar maple. Hart's tongue ferns are usually located in areas that have the greatest diversity of plant species.

Hart's-tongue fern has unusual elongate, non-toothed fronds that are shaped, as the name suggests, somewhat like a deer tongue. Fronds of Hart's tongue fern remain green throughout the winter, with new fronds produced at the start of each growing season. Hart's tongue fernreproduces only by spores. Sori (spore-bearing organs) appear as linear brown stripes along the veins on the leaf underside. The tendency for this species to occur on low boulders and crevices suggests that moist, sheltered conditions are required for sporeling establishment.

Mark Jaunzems discovered this new population in September 2007. Mark has been a seasonal botanist for the Hiawatha every summer since 1995. Every summer he has been in search of this elusive plant. This time he was trying to locate a known occurrence of walking fern (Asplenium rhizophyllum), another rare fern that grows on boulders. Walking fern differs by its much smaller fronds that have very long-tapering tips. However, before Mark got to the walking fern site, he instead stumbled on these cracks in the ground. The Hart's tongue ferns were found on a small previously unknown area of grykes, the deepest ones being three feet deep.

Forest stands containing the original six Hart's tongue fern populations have been given protection by old-growth designation under recent forest planning efforts. Routine monitoring of the sites have taken place since 1999. The new site was in a proposed timber sale area, which has since been dropped from the project. The site will be given similar protection from any future actions that may occur in the area. New discoveries such as this continue to give us improved data on habitat requirements of these rare ferns and enable us to better protect their populations.

For More Information

Sara Davis
Hiawatha National Forest
St. Ignace, Michigan
906-643-7900