The introduction of a column on a particular species of fern got away from me and I ended up writing an entire piece about fern ecology!
This column appeared in the Recorder/Gazette on Apr 23 and the Eagle on Apr 26.
It was a morning in early April and Nature was playing tricks on us. The weather had been cold and raw for days, but then suddenly there was a break from the trend and the temperature soared into the high 60s. There was no threat of rain, but there was a blanket of high clouds shielding us from direct sunlight. It was bright without any shadows – perfect conditions for photography.
Even more interesting was the fact that I had a discrete mission for the morning. Rather than just going for a walk and seeing what there was to be seen, I was headed to a conservation area with a very specific goal in mind. I was looking for a very particular species of fern and I knew just where to go. What I wasn’t prepared for, however, is exactly what I would find.
First, a primer on ferns in general, but please understand that my space is limited and I might not be able to get to every interesting detail there is to tell. When we consider the evolution of life on Earth it is important to acknowledge that life first began in the oceans. For the longest time there was nothing but bare rock on the land as, for about a billion years, there were nothing but ancient bacteria in the salty water. Then photosynthesis evolved and the atmosphere changed. Cyanobacteria were cranking out vast amounts of oxygen for vast amounts of time and the sky turned blue, a hallmark of a “breathable” atmosphere.
Things began cooking and algae evolved, followed by the mosses, which are nonvascular plants that spread water through their bodies by simple diffusion. Mosses need to be kept damp and they require a lot of water for their reproduction. As a result, mosses are rather small plants and they cannot handle dry environments. Plants lived on land, but most of the land was still bare of life. Then there was an important development in the evolution of plants – vascularization. This was the introduction of tubes in the tissues of plants that were specifically meant to distribute water more efficiently.
Ferns were not the first plants to come up with this feature. A group of plants known as the “Cooksonia” were able to develop these structures during the geologic period known as the Silurian Period (443-419 million years ago (MYA)), but today they are extinct. It took a while for a new contender to really figure it out and that group was the ferns. The Devonian Period (419-359 MYA) is widely known as the “Age of Fishes,” but this stretch of time also played host to an event known as the “Devonian Explosion,” when plant life finally took hold of the land.
Ferns figured out how to say goodbye to the aquatic environment. With roots they could grab hold of the soil and with their vascular tissues they could pump water up into larger and larger bodies. They developed spores that could carry their reproductive cells across the land without need of liquid water, but they did maintain a remarkable reproductive cycle that involved two different sorts of organisms. Now we are going to descend into the madness of more detailed Botany, but this is something that freshmen in college can handle, so I imagine you will be able to follow along just as well.
The tall green ferns with their splendid branching fronds are organisms that are described as being “diploid.” This means that these organisms have two sets of each chromosome in their cells, which is the most common sort of state to be in. Birds, rabbits, oak trees and humans are all examples of diploid organisms. For the purposes of reproduction we generate special cells that are described as being “haploid” because they only have one copy of each chromosome, or half the normal number (which puts the ha- in haploid). In mammals these cells are called gametes and are represented by sperm cells and egg cells. When two haploid cells join (fertilization) a new diploid cell results and it grows into a new individual.
Ferns do things a little differently. The diploid ferns produce haploid cells called spores and these will blow across the landscape when conditions allow. But the strange thing about these spores is that they can grow into multicellular haploid organism. These do not resemble the large diploid plants in any way, shape, or form. About the size of a quarter and consisting of a single, flat, rounded “leaf,” these organisms only exist for reproduction. Small structures on the bottom of the leaf produce sperm and egg cells and the sperm cells do require rain to provide a thin film of water in which they can swim their way to the eggs. Once the eggs are fertilized, and a diploid zygote results, the new diploid fern will start to grow, resulting in the death of the haploid gametophyte.
And, despite the fact that I cut corners and ignored huge amounts of biology with wildly irresponsible generalizations that may have some of our more science-minded friends sputtering and spasming as they attempt to reconcile what I have written with what they actually know, I have run out of space. I am including a photo of an Iterrupted Fern (Osmunda claytoniana). A small ant and an even smaller needle from an Eastern Hemlock tree provide context for the size of the leaf blades. You can also see the linear patterns of the vascular tissues that move water throughout the plant.
Well, I am going to have to continue my story about ferns next week. I didn’t even get to the part when my expedition turned out to be a complete success, even though there was a bit of an unexpected twist at the end. What that was, and how it all unfolded, will just have to wait. Until next week, get outside and enjoy the warming days of springtime.