Category: Environment/Sustainability Page 1 of 14

On a bright Sunday afternoon in April, I did something I had never done before. I went for a walk in the woods specifically to look for mosses. No, that’s not strictly true — we were looking for bryophytes. I learned, among other things, that not everything I had always called moss was really moss at all. (The word bryophyte comes from ancient Greek components and literally means “moss plant.”)

The walk was organized by Wild Ones, an undergraduate nature club I’m involved with. Biology Professor Jonathan Shaw, Ph.D., and Blanka Aguero, data and collections manager in the Duke University Herbarium, volunteered to teach a group of undergraduates about mosses and other bryophytes on the Al Buehler Trail adjacent to the Duke golf course.

Bryophytes (which include mosses, liverworts, and hornworts) represent one of several large groups of terrestrial plants. Other groups include angiosperms (flowering plants), gymnosperms (cone-producing plants like conifers and ginkgos), pteridophytes (vascular, spore-producing plants including ferns and horsetails), and lycophytes (an ancient group with about 1200 surviving members). According to Shaw, bryophytes are “the second biggest group after the flowering plants, but the flowering plants are an order of magnitude more diverse.” Aguero says that North Carolina has 462 moss species, 211 liverworts, and 7 hornworts.

Unlike the other terrestrial plant groups, bryophytes are nonvascular, meaning they lack the water transport tissues that other plants use. Without vascular tissue and without lignin for support, bryophytes can’t grow very big because they have no way to efficiently move water from their base to the rest of the plant. Instead, they grow close to the ground and absorb water directly from the environment into their cells.

Despite their preference for damp habitats, bryophytes can live for a long time without water. Some plants (like cacti) survive droughts by storing water, but bryophytes have a different strategy. They go into a state of dormancy, or suspended animation, and simply wait. Then, when it next rains, “they go hog-wild, photosynthesizing again in minutes,” Shaw says.

So if bryophytes don’t rely on constant moisture to survive, why do they like it so wet? Water, as it turns out, isn’t just important for hydration. Bryophytes rely on it to reproduce as well.

“Mosses are the amphibia of the plant communities,” Shaw says. Just as many amphibians can live on land but must return to the water to reproduce, bryophyte sperm has to “swim” to an egg cell to fertilize it. Therefore, they need water in order to reproduce, but they don’t need much. It could be mist from a splashing waterfall or a puddle in the woods or rainwater trickling down a tree. It could even be dew.

The day was warm and sunny, but the ground was dotted with puddles from recent storms. Armed with small hand lenses, we set off down the trail, stopping periodically to scrutinize tree bark, fallen logs, and thick patches of moss on the forest floor.

You need not travel far to find bryophytes. Mosses and their cousins colonize all sorts of hidden nooks: damp logs, trailside divots, tree bark, riverbanks, forgotten corners of backyards. Compared to seed-producing plants, bryophytes tend to have larger geographic ranges, perhaps in part because spores disperse more easily and because bryophytes can survive dry spells. Shaw estimates that about 75% of the moss species found in North Carolina are also found in Europe, and some of them are found in Asia as well.

We learned that most mosses have a midrib in the middle of each leaf, whereas liverworts have no midrib.

“A liverwort,” Shaw explains helpfully, “is like a moss, but it’s a liverwort.”

Liverworts are relatively flat in comparison to mosses because their leaves are in two parallel rows, whereas mosses tend to have a more spiral shape, with leaves emerging from all sides of the stem. The flat appearance of liverworts explains why they are sometimes called scale mosses. Another feature to consider if you’re trying to distinguish mosses and liverworts is the presence of lobed leaves, or leaves with protuberances off the main leaf (think of maple or oak leaves, for example). Some liverworts (but not all) have lobed leaves, but no mosses do.

Aguero and Shaw both point out that the features we use to visually distinguish bryophytes aren’t necessarily the same features that officially set mosses and liverworts apart. The main difference between mosses and liverworts involves differences between their sporophytes.

“It’s not true that if you’ve seen one moss, you’ve seen them all,” Shaw says. They’re small, yes, but they are not all the same.

We looked at one particularly lush patch of moss in the Bryoandersonia genus, named after a Duke professor. If you’re trying to identify trees, Shaw says, you might start with features like whether the leaves are broad or narrow and whether the tree is shrubby or not. With mosses, on the other hand, one of the first questions to ask is whether it’s pleurocarpous or acrocarpous. Pleurocarpous mosses, such as the Bryoandersonia we looked at, tend to have highly branching stems and grow in sprawling patches. The stems of acrocarpous mosses, meanwhile, have little or no branching and grow mostly vertically, often forming tight clumps.

After learning about patches of Frullania liverworts on trees from Aguero, we examined a large clump of liverworts growing beside a stream. Unlike the other liverworts we’d seen, this was a type of thallose liverwort, set apart from so-called leafy liverworts by the presence of thallus (a ribbon-like structure) instead of leaves. We also had the chance to smell it. Interestingly, liverworts also have a distinctive smell, sharp and earthy. The scent can be so strong that you might sometimes smell liverworts before you see them.

According to Shaw, the term liverwort dates back to when botany and herbal medicine were considered largely the same. The so-called Doctrine of Signatures is the long-held idea that plants’ physical features reveal their medicinal uses. Thallose liverworts were thought to resemble livers and were used to treat ailments of the liver, hence the name. Similarly, the walnut looks rather like a brain and was used to treat mental illness, while the Dutchman’s breeches flower (the white flowers are said to resemble pants) was used for sexually transmitted diseases.

Aguero says that some liverworts do contain chemicals with antimicrobial properties, but she advises people not to eat liverworts.

Near the end of our walk, we found something we’d been keeping an eye out for but hadn’t yet seen: moss sporophytes. Bryophytes have a unique life cycle. Most of the time when we see a plant or an animal, it is diploid, meaning each cell contains two full sets of chromosomes (one from each parent). Every human cell, for instance, contains 46 chromosomes—with the exception of female egg and male sperm cells, which contain only 23. Cells that have only one set of chromosomes (like human egg and sperm cells) are called haploid. Plants undergo alternation of generations, meaning that one phase in their life cycle is haploid and one is diploid. In the case of most plants, the dominant and most conspicuous part of the life cycle is the diploid phase, but bryophytes are different. The fuzzy green carpets of moss we see are made of haploid cells, while the diploid phase is short-lived and only appears during reproduction. In mosses, the diploid phase (also known as the sporophyte) resembles thin filaments emerging from the haploid bed of moss. These sporophytes release spores (the spores are haploid) that grow into the next generation of moss.

“I wish we could be like the moss spores and let the wind carry us,” said Kavya Menke, one of the undergraduates on the walk. “Cheaper than Uber.”

Occasionally, I paused my own bryophyte observations to watch others watching bryophytes. I found myself wondering if people are similarly bemused when they see me standing in a swamp with binoculars or crouching down on the way to class to move an earthworm off the sidewalk. I am accustomed to the world of birding, and looking for creatures like dragonflies, snakes, and salamanders feels natural to me as well. But this was a delightful opportunity to enter a world in which I had little to no experience: the shady, damp world of the bryophytes.

If you make a habit of going on walks with birders, you may spend a lot of time waking up before dawn, craning your neck upward, and straining to hear the alleged differences between a dozen kinds of short chirps. If you go out looking for snakes, you might spend a warm afternoon flipping over sun-warmed boards and scanning rocks and other basking spots. Searching for salamanders will likely involve scrutinizing wet soil, leaf litter, and ponds in early spring, possibly on a dark and rainy night. But searching for bryophytes is an experience all its own.

For one thing, you can go at any time of day and be equally successful, seeing as bryophytes neither crawl nor slither nor fly. You can also feel free to move as slowly as you wish. Aguero compares bryologists to lichenologists: “Moss people and lichen people work together frequently,” she says. “We walk similarly slowly.”

You could walk the same trail a hundred times and see it a hundred different ways. You could focus on birds or earthworms or snakes, wildflowers or changing leaves, clouds or trees or rocks. The next time you are in the mood to explore a new world, consider taking a walk — either somewhere new or a path you’ve walked a hundred times before — and turning your attention to the wonderful world of the bryophytes. Pet the moss. Feel its springiness and dampness and softness. Run your fingers lightly over the thin sporophyte stalks and notice how they tickle your palm. Smell the liverworts. See the dark patches of Frullania on a tree trunk. Bryophytes are nearly everywhere. Look for them. Look at them. See them.

Post by Sophie Cox, Class of 2025