Celebrating the Forked Spleenwort

What can I say, I am a total sucker for ferns with "untraditional" fronds. Whereas the tropics offer seemingly endless fern varieties, I find that there is something special about temperate ferns that, for lack of a better phrase, break the mold. I was recently introduced to such a fern. Known commonly as the forked spleenwort, Asplenium septentrionale looks more like a clump of grass than it does a fern.

A closer inspection, however, would reveal that it is indeed a Pteridophyte. It grows on rocky outcrops, including stone walls, throughout the northern hemisphere. Here in North America, it is predominantly found in the Rocky Mountains. It is a small fern that often forms dense clusters in cracks and crevices. Its stems are long, narrow, and grass-like, ending in a flattened leaf blade that often forks at the tip. In typical fractal fashion, these leaf blades fork again at the tips, forming minute pinnae.

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The forked spleenwort has gone through considerable taxonomic revisions since it was first described by Linnaeus in 1753. Originally it was named Acrostichum septentrionale, but was then moved into Asplenium a few decades later. Renewed interest in this species during the mid 20th century saw the forked spleenwort moved to the genus Chamaefilix followed by Tarachia, though these did not gain much scientific credence. As such, it has remained an Asplenium ever since.

Its taxonomic story does not end there, however, as genetic tests soon revealed that a much more subtle and nuanced revision was worth considering. It was discovered that the forked spleenwort existed in two genetically distinct types, a diploid (having two sets of chromosomes) and a tetraploid (having four sets of chromosomes). Researchers found that each group had its own distinct distribution with the diploids centered in southwest Asia and the tetraploids being circumboreal.

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It was clear that a subspecies division was worth considering. Further investigations in the early 2000's revealed the presence of sterile triploid individuals that are believed to be hybrids of the two mentioned above. What's more, the forked spleenwort has been found to hybridize with other members of its genus. It is believed that the more isolated populations owe their existence in part to the isolation of their preferred substrate - these ferns do best on acidic substrates where competition is low - and decent longevity. It has been speculated that genetic differences can be maintained when "mutant" individuals become established and persist undisturbed for long periods of time.  

Regardless of its taxonomic status, the forked spleendwort is nonetheless a charismatic little species. A simple image search will reveal just how pleasant this species is in situ. Even better, its beauty and splendor can be shared by botanical enthusiasts throughout the northern hemisphere. There is something to be said about such species.

Photo Credits: [1] [2] [3]

Further Reading: [1]

Finding The Lobed Spleenwort

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. 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]