The outdoors is often associated with immensity. From towering mountain peaks to expansive, raging rivers, the natural world showcases life on a prodigious scale. While spending time immersed in these landscapes imbues a sense of feeling small, rarely do we set our sights on smaller scenes. Peering closely into an environment reveals an array of biodiversity as overlooked as that which lies beneath the ocean. From the densest rainforests to the sparsest deserts, one group of organisms encompasses an infinitesimal bounty of intricate wonders – the mosses.
Mosses are found in nearly every terrestrial environment on Earth, often thriving in harsh habitats where no other plants or animals can survive. They sprawl over barren rocks, dangle from moist tree branches, wedge into sidewalk cracks, and carpet acidic bogs. Mosses evolved about 400 million years ago and are some of the earliest lineages of land plants. However, their age shouldn’t suggest they are primitive beings or a first iteration of flowering plants. Mosses are defined by a unique lifestyle that has allowed them to persist through ice ages, outlast four mass extinction events, and even live for up to 19 years without a drop of water.
A Wonderous World in Miniature
Over millions of years, the mosses diversified into about 13,000 species, roughly 400 of which are found in West Virginia. “Moss is all around us, but for the most part, people are unaware of the tremendous biodiversity that exists,” says John Boback, an Appalachian environmental historian and field operations manager for Friends of Blackwater.
In dense, drippy rainforests, mosses take the form of wefts and pendants, loose structures with individual shoots that stretch out to capture every droplet of water. In moderately moist environments, mosses form into multi-layered mats, turfs, and plump cushions to optimize the balance between acquiring and retaining water. In arid habitats, mosses grow in small, tightly woven cushions or thin mats plastered against the environment to maximize water storage between rains. Mosses also adjust their growth forms, expanding when water is abundant and contracting when it is not.
Mosses are so well-suited to absorb and store water that their forms are mimicked by many flowering plants. The iconic pendant form of Spanish moss that delicately drapes over tree branches in the Pacific Northwest is actually part of the bromeliad family. In alpine environments, the small cushion shape is adopted by numerous plant species, such as a flowering phlox called moss pink.
Rivaling the complexity in moss forms is their vast array of colors. The color palette of mosses features nearly every shade of green, from pale mint to chartreuse to deep forest green. And it encompasses hues of gold, teal, taupe, silver, white, and black. Crimson sphagnum shines among the deep greens of West Virginia’s wetlands. While stunning, the red pigments also serve as sunscreens protecting the plants from UV damage. Along with adjusting their shape, mosses change color when rain revives them from their dessicated states. “It’s a transformed environment if you look down or look on a tree trunk during a rain,” says Susan Studlar, a bryologist and retired professor from West Virginia University.
Although mosses can be found in almost every type of terrestrial environment, species vary extensively in their habitat preferences. For instance, some prefer to grow on sandstone boulders, while others seek out limestone, which is more alkaline. Copper moss thrives in environments with high levels of copper, even though heavy metals are toxic to nearly all forms of life. While most mosses have it made in the shade, some like it hot. Take the silvergreen bryum moss, which can be found smushed into inhospitable sidewalk cracks across the state.
Forest floors carpeted in dense green mats may appear as just one colossal species upon a cursory glance, but trees provide exceptional microhabitats for a rich variety of mosses. For instance, some moss species only grow at the bases of trees, while others grow further up the trunk. There’s also the knothole moss that, as the name suggests, only grows in tree knotholes. “There’s a tremendous amount of diversity out there,” says Robert Klips, associate professor emeritus at The Ohio State University. “All I have to do is look closely.”
Moss is the Boss
The biodiversity of mosses reflects their adaptions to three fundamental needs of plant life: water, sunlight, and nutrients. “They’re superbly adapted for living close to the ground,” says Studlar. One of the most notable features of mosses is their remarkable ability to rapidly uptake and hold water. For example, sphagnum moss can absorb 20-30 times its dry weight in water. Let’s say there was a lady named Sphagnum. If she weighed 150 pounds, she could absorb 360-540 gallons of water.
The spongey nature of mosses is a product of their extremely thin tissues, which are directly exposed to the environment. As part of the bryophyte taxa along with liverworts and hornworts, mosses typically have leaves only one-cell thick. Most bryophytes don’t have internal plumbing systems or roots to distribute water throughout the plant or absorb nutrients. Instead, they primarily acquire water and nutrients from the air.
Thin tissues allow mosses to begin taking up water within seconds or minutes during a rainstorm, but they also lose water and minerals just as quickly when it dries out. In all but the wettest of environments, a single shoot of a moss doesn’t have a high chance of survival because the opportunity to store water inside leaves is minimal. To hold water, moss shoots group together in colonies. “Their secret to retaining water for a few hours or a few days after a rain is that they can store water between plants, between leaves, and between the leaf and the stem,” says Studlar. A few highly specialized mosses can store water within large, dead cells in their leaves, such as sphagnum and the white cushion moss.
“This plant has the ability, given enough time, to shape entire ecosystems.”
As with any living being, there are trade-offs resulting from their biology. Mosses can survive for long periods of time in between rains by shutting down metabolically, but rapidly rehydrating wreaks havoc on their cells, forcing them to make quick repairs. Because mosses can only grow for a few hours or days after a rain, their growth is quite limited. Most mosses are less than four inches tall, and even the tallest moss, Dawsonia superba, reaches just 20 inches in height.
A Little Help from my Fens
Although small in size, mosses play powerful roles in natural ecosystems. They help prevent flash floods and soil erosion because of their ability to store immense amounts of water. Mosses are also used as ecological indicators due to thin tissues rendering them vulnerable to soil and air pollution. Scientists recently discovered the leaves of a wild moss species shrink, curl, and turn yellow within ten seconds of exposure to sulfur dioxide in the air.
In the wet forests of Appalachia and the Pacific Northwest, moss-covered logs create ideal habitats for hemlock and spruce seedlings to establish. On the forest floor, a tree seedling might be shaded out or buried beneath the leaf litter, “but if it’s elevated on a moss mat of just the right thickness, then it can raise the next generation of trees,” says Studlar.
On an even smaller scale, mosses provide a home for a vast array of microorganisms, including rotifers, tardigrades, nematodes, and microbes. For instance, blue-green bacteria living inside mosses that grow on limestone convert nitrogen from the air into a plant-usable form, enriching the soil for other species to establish and grow. Some scientists think the antibiotic compound sphagnol in sphagnum is produced by a microbe living inside the moss. Sphagnum has been used for thousands of years to treat wounds due to its antibiotic and absorbent properties, including during World War I.
But perhaps the most drastic ecological impact of mosses can be found among the peat—partially decayed vegetation or organic matter mainly comprised of sphagnum moss. Peatlands, a type of wetland, are one of the most valuable ecosystems on Earth. They cover just three per cent of the global land surface, but hold 25 per cent of the world’s carbon, which is more than all other vegetation types combined.
“Sphagnum moss has the ability to completely transform wetlands,” says Sarah Deacon, a biologist at American Public University. When sphagnum moss moves into a wetland, it slowly acidifies the soil and water, changing the wetland from a rich fen, which has a neutral pH and is fed by groundwater and precipitation, to a poor fen, which is more toxic. Because plants are sensitive to pH, rich and poor fens host different compositions of plant species. As the sphagnum continues to decay, it creates a thick mat that eventually isolates the plants from groundwater, marking the transition from a poor fen to a bog. This slow transition is a form of ecological succession, where the composition of a plant community naturally changes over time. “It’s amazing that this tiny plant has the ability, given enough time, to shape entire ecosystems,” says Deacon.
In West Virginia’s wetlands, hummocks of mounded sphagnum undulate atop peat layers, isolated from the groundwater. Blueberry shrubs and other mosses grow atop these hummocks, where conditions are a bit drier than down below. In autumn, these wetlands glow with the white of cottongrass and deep-red cranberries, an alluring contrast to the lime and kelly greens.
Even in winter, when it seems as though all forms of life are dormant, the lively mosses relish in the moisture of snow. In spring, they shoot up stalks of spores that give rise to the next generation, continuing their ubiquitous presence throughout wetlands, forests, and deserts. Whether we notice or not, across every season and in every terrestrial environment on Earth, the mosses are always quietly and beautifully shaping everything around them.
Nikki Forrester is senior editor and designer of Highland Outdoors. She loves hanging out with her fens!
Feature photo: Common haircap moss. Photo by Mark Anderson
Identifying mosses
The multitude of moss characteristics are captured by their peculiar common names. Among the 260 moss species in Studlar’s Annotated Checklist of the Hornworts, Liverworts, and Mosses of West Virginia are the elfin hat moss, heartleaf apron moss, prickly beard moss, Siberian mousetail moss, and common bug-on-a-stick moss. “They must have the kids make up the common names because they’re kind of goofy,” says Klips. Unlike mammals and birds, the common names of mosses aren’t standardized, making it challenging to identify them along with their small stature.
“There’s this mystery about mosses,” says Klips, “A lot of botanists say they don’t know how to identify mosses, but it’s just because they’re small.” Botanists often compare leaves or bark characteristics of trees to identify them, but telling moss species apart often requires a look through a hand lens or under a microscope. To identify bryophytes, botanists look at traits like the shape of a leaf or whether the leaf has tiny teeth, rolled edges, or a midrib. Earlier this year, Boback purchased a compound microscope and a two-volume set of books on the mosses of eastern North America, which contains diagrams of cells in moss leaves. By looking at moss leaves at 100x magnification, Boback can tell whether the cells are square, circular, or squiggly. “That can really help ID those moss species,” he says.
Mosses also preserve their characteristics much longer than flowering plants, which usually wither and turn brown once they’re collected. Klips, noting how moss identification is good for procrastinators, showed me a moss specimen that was collected in 1936. “You spritz it with a little water and it’s as good as new,” he says, “They still have that charm.”
The close inspection and attentive detail required to identify mosses opens a new world of shapes, textures, colors, and interactions on a microscopic scale. As Boback says, “when you get a hand lens or a dissecting microscope and start looking at all the little leaves, you see the tremendous beauty there.”
