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]

Photo by Jakob Fahr/iNaturalist (CC BY-NC)

The association between geology and botany has always fascinated me. The closer you look, the more you can't separate the two. Rocks and minerals influence soil characteristics, which in turn influences which plant species will grow and where, which in turn influences soil properties. Take for instance the case of kimberlite.

Kimberlite is a volcanic rock whose origin is quite intense. Kimberlite is found in the form of large vertical columns, often referred to as pipes. They are the result of some seriously explosive volcanism. Intense heat and pressure builds deep within the mantle until it explodes upward, forming a column of this igneous rock.

Over long spans of time, these pipes begin to weather and erode. This results in soil that is rich in minerals like magnesium, potassium, and phosphorous. As anyone who gardens can tell you, these are the ingredients of many fertilizers. In Africa where these sorts of pipes are well known, there is a species of plant that seems to take advantage of these conditions.

It has been coined Pandanus candelabrum and it belongs to a group of plants called the screw pines. They aren't true pines but are instead a type of angiosperm. Now, the taxonomy of the genus Pandanus is a bit shaky. Systematics within the family as a whole has largely been based on fragmentary materials such as fruits and flowers. What's more, for much of its taxonomic history, each new collection was largely regarded as a new species. You might be asking why this is important. The answer has something to do with the kimberlite P. candelabrum grows upon.

There is something other than explosive volcanic activity that makes kimberlite famous. It is mostly known for containing diamonds. In a 2015 paper, geologist Stephen E. Haggerty made this connection between P. candelabrum and kimberlite. As far as anyone can tell, the plant is a specialist on this soil type. As such, prospectors are now using the presence of this plant as a sort of litmus test for finding diamond deposits. This is why I think taxonomy becomes important.

If P. candelabrum turns out not to be a unique species but rather a variation then perhaps this discovery doesn't mean much for the genus as a whole. However, if it turns out that P. candelabrum is a truly unique species then this new-found association with diamond-rich rocks may spell disaster. Mining for diamonds is a destructive process and if every population of P. candelabrum signals the potential for diamonds, then the future of this species lies in the balance of how much our species loves clear, shiny chunks of carbon. A bit unsettling if you ask me.

Further Reading:
http://econgeol.geoscienceworld.org/content/110/4/851.full