Plant of the Week
American Hart’s Tongue Fern (Asplenium scolopendrium L. var. americanum (Fern.) Kartez and Gandhi)
Hart’s Tongue Fern is a rare treat for the eyes; it is so green, glossy, and large that it defies reality. The elegant, smooth, unserrated fronds are 20 to 40 cm in length and look decidedly tropical and incongruous in the northern forest they inhabit. These huge fronds are hopefully tucked safely beneath the snow during the winter as the species is evergreen and perennial.
Hart’s Tongue Fern can be found in discrete habitat within a very few shaded, moist, intensely green northern deciduous forests. An epipetric fern, it grows within small cracks in large rocks, the rock fissures usually no more than a foot above the moist soil. The white limestone it inhabits is luxuriantly covered by myriad green moss species and also supports other rare epipetric fern species such as Walking Fern (Asplenium rhizophyllum), Green Spleenwort (Asplenium trichomanes- var. racemosum), Slender Cliff Brake (Cryptogramma stelleri), and Laurentian Fragile Fern (Cystopteris laurentiana). It is a truly beautiful sight.
Habitat in Michigan and New York is within the Niagara escarpment on shaded, moist boulders and ledges. This epipetric fern requires Silurian limestone, a substrate of high magnesium content. The Niagara escarpment was formed approximately 450 million years ago by corals inhabiting a vast and tropical inland sea and slowly was transformed into a dolomitic limestone.
The distribution of Hart’s Tongue Fern is very limited and discrete. It is found in two counties within the eastern Upper Peninsula of Michigan (about 12 occurrences); a few isolated, tiny colonies in Alabama (on another karst feature: cave entrances), and in central New York, which harbors 90 percent of the United States population. In contrast, this fern is locally abundant on the Bruce Peninsula of Ontario, Canada, again on in the Niagara escarpment. Other varieties of this fern are distributed in Japan and Europe. The Hiawatha National Forest of the Eastern Region of the Forest Service is home to nine of the Michigan occurrences and is the only National Forest to harbor this species.
Hart’s Tongue is federally threatened in the United States (listed in 1993); state endangered in Alabama, Michigan, and Tennessee; threatened in New York; and Sensitive or Special Concern in Ontario.