Moss, Small Wonder Beneath Our Feet

Moss in Every Nook and Cranny

I’ve been fascinated by moss for as long as I can remember. As a young child, I loved touching these soft, natural green carpets in the woods behind our home. For me, there’s something magical about this tiny non-vascular plant that seems to hug so many varied surfaces near the ground, including rocks, fallen logs, shady patches of soil, tree bark, streambeds, and damp crevices on the forest floor. Surprisingly, mosses are found all over the world in almost every climate and ecosystem, from tropical forests to the Rocky Mountains and Eastern woodlands of the United States, to alpine and polar regions, and even in arid deserts. Indeed, mosses inhabit places where most other plants cannot possibly survive.

Remarkably resilient, these primitive beauties, the first plants adapted to life on land, have been around for 450 million years. With more than 15,000 different types of moss, these miniature specimens have demonstrated exceptional survivability and adaptability over time. How appropriate that George Schenk calls moss “nature’s chosen ones” in his informative book titled Moss Gardening.

 

 

What is moss? What structures keep it alive?

Mosses are classified as Bryophyta, along with liverworts and hornworts. Like other green plants, Bryophytes need sunlight, water, carbon dioxide, and minerals to make their own food through the process of photosynthesis. However, certain distinctive botanical characteristics make this group of shade-loving plants rather unique. Instead of a root system, mosses have hair-like filaments called rhizoids that enable astonishingly strong attachment to various surfaces. That makes it possible for moss to cling to boulders and other substrates, defying gravity and growing in every direction.

The simple structure of mosses, which lack cellulose to support woody cell walls, does not have a vascular system for transporting water and nutrients. As a result, mosses rely on capillary action and osmosis to gather moisture from their surroundings. In her book, Gathering Moss, Robin Wall Kimmerer refers to mosses as masters of minimalism who “engineer the movement of water by harnessing the attraction of water to surfaces — without expending any energy of their own.” How clever is that!

Bryophytes such as mosses are poikilohydric, which means that the water content of the plant changes along with the water content of its environment. Mosses tend to live in porous, tightly-packed colonies, which increases their capacity for water collection and retention. And, it’s not unusual for several different varieties of moss to live harmoniously in these colonies.

Moss leaves are small and thin (single cell thickness) and have no cuticle, a waxy substance that covers the leaves of most other green plants. This structure allows moss leaves to absorb water from mist, dew, and rain rather quickly and become saturated to sustain life.

Moss growth occurs only when moss is wet, but even after losing over 95% of its water content, it can still survive. During those dry times, moss is actually in a dormant phase. Moss plants can remain dormant for a few weeks, months, or even years, depending on the species. Despite looking misshapen and desiccated, moss will generally be revived whenever moisture becomes available. Quite amazing!

Mosses have several other adaptations that enhance their survival in adverse conditions. Due to biochemical substances that protect plants from stress, called internal phenolic compounds, mosses are able to enter a period of dormancy in order to live through subfreezing temperatures and excessive heat. These compounds also make mosses taste awful, which gives them protection from insects and other animals that might otherwise dine on them. In addition, phenolic compounds provide robust protection for mosses against diseases. These impressive strategies help provide robust protection for mosses against desiccation, predation, and disease.

Moss Reproduction 

Unlike familiar flowering plants, mosses do not reproduce with seeds. Instead, mosses have three different methods for reproduction: with spores (sexual reproduction in two stages), with fragments that clone themselves (asexual reproduction), and with gemmae (vegetative reproduction, also asexual).

For sexual reproduction, the process of spore dispersal begins with gametophytes, tiny moss plants that may be either male or female. Male gametophytes produce sperm cells, and female gametophytes produce egg cells, each with only one set of chromosomes. The microscopic male organ, called the antheridium, releases sperm cells that must swim over the wet surface of moss, searching for the microscopic female organ that encases the egg, called the archegonium. As you might imagine, during dry times this method of reproduction may not be successful.

If fertilization occurs, spores that contain both X and Y chromosomes will develop. This creates sporophytes, which form setae, or stalks, that stand upright on the top of moss. Without its own internal method of transport, mosses must rely on natural forces to disperse their spores. Wind and rain are the primary means of distribution, but animal movement may assist in this process. If spores land in hospitable locations, they will grow into new moss plants, continuing the life cycle.

In fragmentation, small pieces of moss that have been torn off and displaced by water, wind, or animals can resettle in new locations and begin to grow into moss that is identical to the parent plant. For those who want to get started with moss gardening, this method, similar to cloning, is a relatively easy way to encourage moss reproduction. In vegetative reproduction, small cups filled with gemmae cells (Latin for jewels) grow on moss stems or leaves. These gemmae, also called propagules, can be dispersed with water, landing in new places. They will then develop into moss gametophytes (described above) to start the life cycle all over again. Awesome that moss reproduces in three different ways!

Opportunistic Survivors

Now that you’ve expanded your knowledge of moss, you might be wondering why it’s creeping into the dim north edges of your lawn, surrounding the shady base of trees in your yard, or filling in the dark sidewalk cracks leading to your front door. You probably haven’t cultivated that moss, and some of you aren’t so sure you want it. Reality check: Moss has a tendency to sneak into places where other plants struggle to get going, and once established, moss is quite hardy.

Before removing moss from those areas, perhaps you should reconsider. After all, moss requires no mowing and little supplemental watering, except in times of severe drought. Moss is naturally disease-resistant, and it requires no chemical treatments that end up polluting waterways and groundwater. Moss tolerates infertile soil, and it stays green all year, even during cold winters. In my mind, moss is an unsung hero that silently slips in to beautify the landscape.

Environmental Benefits

Here’s a brief introduction to the countless benefits of this year-round superpower of green delight that shows up all over the world. First of all, mosses play an important role in carbon sequestration, the process by which carbon dioxide is removed from the atmosphere and stored in solid or liquid form. With climate change posing a significant threat to the health of our planet, mosses make a notable contribution as the largest land repository for carbon storage on Earth. For example, Sphagnum peatlands sequester between 198 and 502 billion tons of carbon.

Moss, with its strong rhizoids that hold onto the soil, can be a significant factor in erosion control. When planted on hillsides where rushing water is a problem, moss will absorb some of that water and slow the rate of flow. In drainage ditches and other areas where fast-moving stormwater can be problematic, moss can reduce flash flooding and run-off as it captures sediment and decelerates the water flow.

Sphagnum mosses are particularly useful for water filtration and wastewater treatment. Moss can trap oils, detergents, dyes, and other organic matter that should be kept out of rivers and streams. Furthermore, mosses can capture toxic discharge and unhealthy pollutants from public waterways, such as mercury, copper, silver, and lead. At former mining sites, moss can help the land rebound back to better health by absorbing heavy metals and growing undeterred on barren landscapes. In areas with severe winter weather and frequent use of salt and other chemicals on impermeable roadways, moss can soak up these contaminants and continue to thrive. What an incredible survivor!

If you need further testimony that moss is not only valuable but also attractive, stroll through nearby damp forests and notice the moss clinging to rocks and climbing up tree trunks. During a recent visit to the mountains of western Maryland, I was astounded by the sight of prolific moss colonies along shady trails. A mystical world of gentle softness surrounded me as I hiked through the woods. Serenity at its best!

Types of Moss

At a basic level, there are two types of moss: clumpers (Acrocarpus species) and spreaders (Pleurocarpus species). Clumpers are ball mosses that form dense, upright, circular mounds or mats. Spores emerge from the top of their vertical stems. These mosses resemble cushions and work well when positioned between rocks or pavers. Spreaders, which grow sideways, look feathery, almost like tiny ferns. Their spores form along the stems. These carpet-style mosses work well as filler for lawns with bare spots or as replacement for turfgrass in shady areas.

Identifying mosses is rather challenging because certain important characteristics are microscopic. It’s possible to distinguish some features with a good handheld lens, but careful observation and field guide references may be necessary. For those who are eager to try cultivating moss, the following types are relatively easy to grow. Excellent close-up views of these mosses are available at this Bryophyte portal (search by the scientific name of each moss).

• Brachythecium rutabulum, or foxtail moss, is a common “spreader” moss that grows in horizontal mats. Given damp northern exposure, this moss will thrive, readily filling in bare spots where grass and other sun-loving plants won’t grow.
• Hypnum imponens, also called log moss or feather moss, is another “spreader” that grows easily on various substrates, with preference for logs and tree bases. Its individual moss plants are fern-shaped, and they do fairly well during dry periods.
• Bryum argenteum, or silver moss, is a “clumper” that grows just about everywhere, from rooftops to pavement cracks, as well as along hiking trails. It tolerates sun and requires only occasional water, so it’s a great low-maintenance choice.
• Dicranum scoparium, known as broom moss, tends to look windswept. It’s an exceptionally soft “clumper” that loves to grow on rock ledges and poor soil. This is a rich green moss that retains its color, even when partially dried out.

Gardening with Moss

Anyone dreaming of moss gardens can start by conceptualizing designs that could complement an existing landscape. Begin by asking key questions, such as:

• Where are the shady areas? Are there any spaces where moss would thrive?
• How much moisture is available? Is there a source of water nearby?
• From which directions could mossy patches be viewed?
• On or between which existing surfaces might moss be a good partner?
• Is there room for pathways that allow wandering near beds of moss?
• What other plants would be good companions for moss?

You may also want to have your soil tested because moss likes acidic soil and will do best if the pH is between 4.5 and 5.5. Sulphur or aluminum sulfate, available at agricultural supply stores, can be added to amend your soil, if needed. Be sure to consult reputable sources (see references below) to find out the recommended amounts.

Browse books or websites with photos of moss gardens to kick-start your design plans. Make draft sketches and revisit your ideas, adjusting them as you continue to dream about the natural tranquility and beauty of moss. When you have a plan and are ready to try cultivation, consider these tips from Dale Sievert, who has spent 50 years creating moss gardens in Wisconsin (see The American  Gardener citation below).

• Start small – Moss is a slow-growing plant, so it’s wise to see what happens in patches no more than one or two square feet in size before expanding. Depending on the type of moss you choose, it may take from six months to a year or two for moss to be well-established.
•  Try several places – Choose appropriate sites in your yard, place moss in those locations, and then determine where moss seems to thrive over a period of time.
• Use your own – If possible, gather bits of moss from a few spots on your property and re-plant it where you’d like to begin a mossy patch. For best results, match conditions of the original site with the new site.
• Anchor them down – Water the new patches of moss and step on them gently to anchor them in place.
•  Take good care – Observe fresh moss beds, keep them moist, and remove extraneous sticks, leaves, and other unwanted materials that land on top of the moss. A soft broom may work for this task.
• Weed carefully – Moss may be disturbed if you pull up weeds growing within it, so use two hands (one for holding moss down, and one for pulling on weeds) to carefully dislodge young weeds when they first appear.

Feel free to be creative as you consider how, when, and where eco-friendly moss might add graceful patches of wonder beneath your feet. And for those who don’t see themselves cultivating moss, consider making friends with the moss that shows up in your yard and just let it be.

Commercial Sources of Moss

Mountain Moss in Brevard, NC

Moss Acres in Honesdale, PA

Print References

Cullina, William. (2008). Native Ferns, Moss, and Grasses. New York, NY: Houghton Mifflin.

Kimmerer, Robin Wall. (2003). Gathering Moss: A Natural and Cultural History of Mosses. Corvallis, OR: OSU Press.

Martin, Annie. (2015). The Magical World of Moss Gardening. Portland, OR: Timber Press.

Schenk, George H., (1997). Moss Gardening: Including Lichens, Liverworts and Other Miniatures. Portland, OR: Timber Press.

“Moss Garden Masterpiece.” The American Gardener. (Mark Dwyer, Sept/Oct 2020, p. 18-23).

Online Resources

Bryophyte Flora of North America hosted by the Missouri Botanical Garden

Bryophyte Ecology e-book by Janice Glime at Michigan Tech

CNABH Portal Home (bryophyteportal.org) consortium of North American Bryophyte Herbaria