The gleaming white magic of a winter wonderland enticed me outside after breakfast. With our first snow on the ground, the air tasted fresher, the brisk cold nipped my cheeks awake, and the world felt new.
Above me stretched a lacework of light and shadow against the widening blue. All around me, the thin layer of sticky snow created lush patterns on the forest floor. Pebbles in the driveway, twigs on the ground, and ferns leaning over became works of modern art under their crust of white. Christmas tree-sized balsam firs hugged their snow-laden branches close. In the understory, mini trees did the same.
Only those mini trees aren’t really trees, at least not anymore. You might know them as ground pine, princess pine, or club moss. If you’re botanical, you might even know them by their genus Lycopodium (Greek for little wolf foot). None of those names are entirely accurate, though. These definitely aren’t pines, or mosses (or wolves!), and new DNA studies have made the scientific classification more complicated, too.
Lycopodiums are beautiful and amazing, though, and harken back to the Devonian and Carboniferous Periods more than 300 million years ago. At that time, North America was part of the supercontinent Pangea, and the eastern United States was positioned near the equator. Beautiful plants, gigantic insects, and strange forests covered the land. Increased precipitation, carbon dioxide, and oxygen created a very different world than we know today.
The tropical climate produced extensive swamps dominated by tree-like or “arborescent” lycopsids that diverged from a common ancestor of our present-day clubmosses. These were some of the first plants to grow secondary tissue (wood), which was needed to support their impressive heights of 50 meters (164 feet). That is taller than the tallest white pines currently growing in Minnesota or Wisconsin.
What’s crazy is that they couldn’t increase their girth along with their height. Each tree had to begin its life by growing its trunk as wide as it would ever be. The thick stump grew upward into a pole of the same diameter. Leaves – also known as microphylls because they only have a single vein down the center – grew along the trunk. With only the single vein, though, they had no way to transport the sugars produced by photosynthesis. As the tree gained height, the lower leaves fell off (creating a distinctive pattern on the trunk, and earning them the nickname “scale trees”), and the lower trunk essentially became dead tissue. At some predetermined height, the tree branched a certain number of times, reproduced, and died.
With such a “quick and cheap” lifestyle, the arborescent lycopsids both grew and died rapidly. This allowed them to dominate habitats following short-term disturbances (like frequent fires), and leave behind a tremendous amount of woody debris in those tropical swamps. If you tried to imagine such a swamp today, you’d probably envision a mucky forest full of rotting logs. Back then, however, fungi hadn’t yet developed a good way to decompose wood – especially the tough, brown lignin in wood, and charcoal – so tree trunks would have lain around for years.
Charcoal? In a soggy swamp? There is evidence that the high oxygen levels in the Carboniferous Period atmosphere allowed large-scale firestorms to sweep across the globe. The charcoal and other organic matter left in the swamps was eventually buried and turned into coal.
The unique conditions present during the Carboniferous Period may never be repeated on Earth. As carbon in the air became locked up in coal deposits, in the explosion of land plants, and in limestone beds under the ocean, the conditions no longer supported giant lycopsids. They shrank into diminutive quillworts, while their cousins became the clubmoss we know today. Complex plants with seeds, extensive vascular systems, and trunks that could grow out as well as up succeeded instead.
The branches of this new forest closed in over my head as I appreciated the beauty of our current non-tropical weather. Tiny, snow-capped lycopods dotted the understory landscape—their diminutive size hiding an immense history and adding to the magic of the forest. Nature is surprisingly old and always new.
Lycopodiums (also known as club moss), dominated tropical forests 300 million years ago. Today, they are tiny, understory plants beneath a new era of trees. Photo by Emily Stone.