When looking for ferns, it is easy to have a specific kind of search imagine in your head. Your mind's eye is tuned into the long, lacy look of dissected fronds but there are ferns out there that will challenge you to break that mold. I have had the wonderful privilege of meeting some of these fern species this year, but there is one species in particular that has really stuck out.
Meet the American hart's tongue fern, Asplenium scolopendrium var. americanum. The hart's tongue, as you can see, is absolutely striking. Its long, slender, uncut fronds form a disheveled rosette and the sori running along the underside make each frond look like a big, green centipede. Asplenium scolopendrium itself is a wide ranging species of fern, growing on limestone outcroppings throughout Europe but populations in North America are rather sparse and disjunct. In fact, the U.S. Fish and Wildlife Service has listed it as a threatened species. There are some morphological distinctions between the European and North American populations but the major difference is in their number of chromosomes. European hart's tongues are diploid whereas North America's are tetraploid. Because of these differences, botanists consider them distinct varieties.
Why the American variety is so rare is not fully understood, but human activities have not helped matters. Mining, logging, and development have wiped out many historic populations of these ferns. Their habitat specificity mixed with their already low numbers make for little to no range expansion for most populations. They seem to grow in close association with dolomitic limestone, which is high in magnesium.
They also seem to rely on a specific mix of bryophyte communities, low light levels, moisture, and snow pack in order to persist. Spores that land on significant bryophyte patches seem to germinate better. Young ferns seem to perform better in mixed light levels, especially near canopy gaps. It has also been shown that snow pack is directly correlated to the vigor of each population. In years with below average snow pack, the plants seem to have trouble retaining enough moisture to survive.
This is such an incredible species of fern. To lose it would mean a serious loss for our planet. There is a good effort being put forth to protect, study, grow, and form a deeper understanding with the American hart's tongue fern. The more we learn about this species, the better we can understand what it is going to take to ensure that it persists far into the future.
Photo Credit: James Johnson (http://imgur.com/a/J1Ez5)
Further Reading:
http://www.fws.gov/northeast/nyfo/es/amhtfrecovplan.pdf
http://www.bioone.org/doi/abs/10.3159/TORREY-D-11-00054.1…
http://www.fs.fed.us/
http://www.centerforplantconservation.org/