Finding The Lobed Spleenwort

This is the story of my first encounter with a hybrid fern back in the spring of 2016.

I love exploring geologically diverse areas. The more rock outcroppings the better. You never know what you are going to find in the numerous nooks and crannies, each with their own unique microclimate. This weekend a few of us decided to get out of town for a bit and explore southern Illinois. You can imagine my excitement then when I laid eyes on a rugged terrain filled with ridges and rock outcrops. With only a few days to botanize, I didn't waste any time. 

The woods were alive with early spring ephemerals. Trilliums, Phacelias, Claytonias, and Dicentras filled the forest with a soft pallet of colors. Along the numerous cliff faces I was finding lots of walking ferns already awaking from the mild winter. At one point I found myself following the meandering path of a small stream. Along each side were small cliffs that were carved out of the surrounding bedrock over eons. Their appearance was softened by the myriad species of lichen and moss that carpeted their surfaces. Upon this moss, small ferns and plants are able to take root. My eye kept leaving the creek bed, finding its way along the rocks, looking for anything peculiar that might catch my eye. That's when I saw it. 

Sticking out of a small hole in the rock was an interesting looking fern. At first glance I thought it was another walking fern. Something was off though. It's outline didn't look right and I had to investigate. Its fronds looked lobed. Indeed they were. This was no walking fern but I wasn't ready to jump to conclusions just yet. I pulled out my fern guide in order to confirm my suspicions. 

What I was looking at was a hybrid. Not just any hybrid either. This unique looking little plant is known scientifically as Asplenium pinnatifidum - the lobed spleenwort. I was just lucky enough to be botanizing on the far western portion of its range. Although it is far more prevalent in the Appalachian Mountains, this hybrid is by no means common. I was very lucky to have spotted it.

It is the result of a chance mix between the walking fern (Asplenium rhizophyllum) and the mountain spleenwort (Asplenium montanum). My original inclination towards walking fern wasn't far off. One interesting aspect of this particular hybrids biology is that it is an allotetraploid. Instead of getting one set of chromosomes from each parent (diploid), this little fern gets a full compliment of chromosomes from each, giving it 4 copies total. 

Because it has a lot of functional chromosomes to work with, the lobed spleenwort is fertile. As such, experts have given it the designation of a true species. It can even go on to produce subsequent hybrids. It has been reported to hybridize with other members of the genus Asplenium, however, the offspring produced from these crosses are usually sterile. 

I looked around the area to see if I could find more. In total I only saw two. That's not to say more aren't out there. There are plenty of rock ledges and cliffs that make this region so uniquely beautiful. It is likely that this hybrid fern has unknown populations growing out of reach of watchful eyes. Long may it be that way. 

Further Reading: [1] [2] [3]

Ruta-Muraria

In my opinion, the smaller a plant is, the more character it has. Wall rue (Asplenium ruta-muraria) is a wonderful demonstration of this. The genus of ferns to which it belongs, Asplenium, is rather large, containing somewhere along the lines of 700 species worldwide. 

Wall rue can be found growing both in North America and Europe. Its distribution is a reminder of the great land bridges that once connected the continents back when ocean levels were much lower than they are today. The specific epithet "ruta-muraria" roughly translates to "bitter herb of walls." Along with its common name, these seem to hint at where this tiny fern likes to grow. Indeed, at least in Europe, this is a fern of stone walls, growing among the myriad cracks and crevices where microclimates are favorable for its spores to germinate. 

In North America, however, wall rue seems to be a bit more picky. Wall rue is a calciphile meaning it can really only be found in abundance on natural limestone outcroppings. As a result, it is considered a threatened or endangered species throughout most of the continent. The aspect of its habitat I find most interesting is that the limestone it relies upon is the result of an ancient sea that covered parts of North America during the Silurian Period some 443.8–419.2 million years ago. If it were not for the solidified remains of ancient marine organisms, wall rue and many other plant lineages would not be here, at least not in the way in which we know them. 

Another interesting aspect of wall rue biology is that this little fern is helping paleontologists in Europe discover potential glacial refugia - ice free areas where plants and animals were able to survive during the height of glaciation. Refugia were likely epicenters of biodiversity, which expanded to recolonize the continents once the ice sheets receded. 

Wall rue, as well as other rock ferns in the genus Asplenium occur in two forms in nature - a diploid form with two sets of chromosomes and a polyploid form containing multiple sets of chromosomes. Polyploids arise from mutated diploids and can be found growing over a wider range than their more restricted diploid parents. By studying the relatedness of different diploid populations, researchers are able to deduce where some glacial refugia may have been located. In this way, these tiny little ferns are offering a rare but clear window into the Earth's long gone past. 

Further Reading: [1] [2] [3]

American Heart's Tongue Fern

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/