Club Moss, Ancient Heritage
What is club moss? I’ve never really asked this question until recently. I’ve seen them frequently in my walks in the woods but ignored them. After all, they are spore-producing vascular plants, and I was on a seed-collection mission when I’m out in the field. Well, spores act like seeds, but their reproductive system is quite different from that of seed-bearing plants. For one thing, you would need tons of spores to germinate just a few in the wild. Even if a club moss germinates, it will have to go through two generations of its life cycle in order to become a sexually mature plant. In some cases, that will take more than a decade! The most common spore-producing plants are mosses, liverworts, and ferns. So, except for some fern species, I ignored these “lower” plants in my walks.
That was until I sort of discovered lichens. Ever since I learned a little about lichens, I realized that I have overlooked the pioneering roles these ancient, “lower” plants, (such as mosses, hornworts and liverworts), have played as the first true land plants. The land was inhospitable to life before 500 million years ago. According to earth scientists, plants first appeared on land about 460 million years ago. They were bryophytes (a group of plants consisting of mosses, hornworts, and liverworts) who successfully established themselves on dry land. Until then, it was just green algae floating along the coastal edges.
I may not use spores to germinate these primitive plants, but I became curious about mosses, and to some extent liverworts, that I see everywhere while looking at lichens. Lichens are often found in the company of mosses. The bryophytes have kept their ancient ways of living and are still playing a vital role by colonizing and thereby helping other plants to establish themselves in otherwise inhospitable plots. I keep finding intriguing-looking sphagnum mosses and other kinds of mosses, but it is a challenge to identify these tiny and seemingly identical-looking creatures without a microscope. As lazy as I am, I soon got discouraged with the idea of learning more about mosses and liverworts. (I have never actually spotted a single honewort in all of my walks.)
That’s when club mosses popped into view. They are not actually mosses, of course. But they are still one of the earliest land plants, coming soon after the bryophytes. For me, it helped that they are most definitely macro. Besides, there seems to be only four different species of club moss existing in our region anyway, as far as I am able to tell. (I learned that world-wide, there are about 1,000 species of club mosses.) Club mosses are inconspicuous in our local forests, but they can readily be found, in small quantities, if you look. You will find them as both small or large clusters, thanks to their creeping roots. All of them are connected by these running roots.
My real fascination to club moss, however, has little to do with its morphology or its ecology. It has everything to do with its ancient heritage. It is hard to visualize vast rainforests that covered most of the land about 300 million years ago. That’s even way before dinosaurs appeared! (Dinosaurs had to wait for another 100 million years or so before they become the rulers of the land.) It is even harder to imagine that the Lycopodiopsida, the class of club mosses, were rulers of those forests. They weren’t as small as they are right now. Their height then reached to 100 feet. We call this the coal-bearing period: Carboniferous.
According to scientists, the Carboniferous Period (360 to 300 million years ago) generally had a more uniform, tropical, and humid climate, rich in carbon dioxide. Basically, there were no varying seasons, much like modern day tropical forests. These conditions proved favorable for the first terrestrial vascular plants. They didn’t have to depend on algae to photosynthesize. These were our very first real forests. The vast swamp forests were dominated by clubmoss trees, giant ferns and tree-like horsetails, along with giant invertebrate animals, like gigantic millipedes and dragonflies.
Eventually, fast forward to the future, the forests collapsed. Scientists speculated that the collapse was due to climate change. Glaciers that appeared near the South Pole spread. It got cooler and drier. As the climate changed, the first forests were buried under the soil, and due to the heat and pressure, were turned into coals. (It’s interesting to note that during this time there were no lignin-eating fungi. These did not appear until much later, and thus dead trees didn’t decay; instead they accumulated deep in the soil). They became a rich supply of coal that fueled the success of our modern civilization.
I am looking at the remnants of ancient forests. After several hundred million years, they are still with us. They are now only a few feet tall, perennial, evergreen, and still spore-producing. Unlike bryophytes (that group of plants consisting of mosses, hornworts, and liverworts), the club moss possessed vascular tissue. They had developed real roots and lignin (the structural backbone of woody plants) and primitive yet real leaves that had chlorophyll, a key component in the process of photosynthesis.
Yet, club mosses, along with bryophytes, seem to have been arrested in some evolutionary transition. They have this rather primitive set of life cycles or phases. The life cycle of the club moss has a sexual phase (the gematophyte) and a spore-producing phase (the sporophyte). If a single spore out of thousands germinates successfully, it produces a pre-sexual body called the prothallus. They are mostly underground. They stay underground up to 7 years and take up to 15 years to mature. Because they are underground, they cannot receive solar radiation and therefore are not photosynthetic; they cannot produce their own food. They rely on mycorrhizal fungi for their nutrition.
After 15 years or so, the antheridia (the male gamete) swims to another part of the same prothallus to meet an archegonium (the female gamete) to consummate the sexual act. You can just imagine. From this, the sporophyte phase of the club moss begins. Unlike the gametophyte, the club moss’s sporophytes are photosynthetic. What we see is only this sporophyte phase of the club moss.
In our region, I found four different species of club moss. Their generic names have gone through many changes; the species names less so. The common names mostly reflect the form of the plant (“ground cedar”). The common name (“club moss”) describes the club-like appendages at the tip of the stalk that holds the spores. Here are my four:
Diphasiastrum digitatum (Common Running Cedar or Common Running Pine)
Diphasiastrum tristachyum (Ground Cedar or Running Cedar)
Dendrolycopodium obscurum (Common Ground Pine)
Huperzia lucidular (Shining Moss)
Being arrested on an evolutionary path or not, club moss is a survivor. Perhaps its survival tool is keeping a less-prominent stature. You are far less vulnerable if your size is small and your ecological footprint is tiny. Minimal influence in return for minimal harm, so to speak.
While nobody pays much attention to them, club mosses have been quietly living their lives, witnessing the world for over 300 million years. They have withstood all the great and small changes that the Earth has gone through. They witnessed the major movements of the Earth’s crust: from one supercontinent (Pangaea) and just one ocean to numerous continents and oceans. They saw the rise and fall of the dinosaurs and the rise of the mammals. They have also seen several dramatic climate shifts and the extinctions of life forms that followed.
It is generally known that humanity, loosely defined, started 6 million years ago. The Homo genus, (including our own species, Homo sapiens), started about 2 to 4 million years ago, according to some reckonings. Like club mosses and dinosaurs in other times, Homo sapiens have become the rulers of the Earth today. But at this point, at the onset of anthropogenic climate change, I cannot help but wonder if Homo sapiens will follow a fate similar to club mosses and dinosaurs: damaged but able to adapt to profound change. Club mosses have reduced their physical size, and dinosaurs evolved into birds. These are winning transformations.
If our species survives long term, what would that look like? What kind of self-transformation would be required to survive? Do we have that in us? Are we willing to change? Could we last 300 million years, as has the lowly club moss?
Written by Lisa Bright.