What I Learned on a Moss Walk

If you happen to be driving along the Blue Ridge Parkway in North Carolina and stop at the Wolf Mountain Overlook at milepost 424.8, your natural inclination will be to look at the butterflies swarming over the wildflowers that cascade down the mountainside. That's a grand view, but there's a far more interesting one behind you, though you'll have to get close to appreciate it.

Backtrack across the road to a massive wall of exposed granite and take a close look. You'll be rewarded with a floral fantasyland. Growing out of the towering granite and along its roadside edge is an example of one of the most diverse native flora in the Appalachians. Participants in a moss field trip, part of the 2018 Cullowhee Native Plant Conference, oohed and awed over at least four species of St. John's wort, including a very rare one. They were blooming alongside a long cast of characters — an undersized hydrangea somehow still flowering away; two species of bluets; two uncommon plants, grass of parnassus and tasselrue; Michaux's saxifrage; the Blue Ridge dwarf dandelion; Bowman's root; sundews, a carnivorous plant; and liverworts.

These plants were all there because of the understated star of the show: mosses — more than a dozen that created the perfect conditions for these larger plants to thrive.

How does moss grow?

"Mosses get started in little nooks and crannies in the rock where soil has collected," Ann Stoneburner told the plant enthusiasts attending the conference hosted by Western Carolina University. Stoneburner, formerly a research biologist at the University of Georgia, was leading the field trip with her husband, Robert Wyatt, professor emeritus of botany and ecology at the University of Georgia. "Mosses don't have roots," Stoneburner continued, "but are held in place by little hair-like structures called rhizoids."

Wyatt took it from there: Carbonic acid forms, breaking down the rock and deepening the pocket in which soil collects. The moss itself also produces organic material that can be incorporated into the soil and enhance its capacity to hold water. The process creates a more favorable microclimate for the establishment and survival of certain plants that sprout when a seed lands in the moss.

What makes this floral ecosystem possible is that water is constantly dripping down and through the rock. So much water, in fact, was seeping down the side of the mountain and onto the plants growing there during our visit that droplets falling from the plants created tiny splashes in pools of water by our feet, giving the illusion that it was raining. "This is called a vertical seepage bog," said Wyatt. This type of bog occurs at similar elevations on natural vertical rock faces and is pretty rare. "This part of the Appalachians is a red spruce-Fraser fir forest," he said, explaining how vertical seepage bogs are created. "The moss floor at the top of the mountain captures rain water and then slowly discharges that water, allowing it to seep down through and over the rocks."

This is the first thing I learned about mosses on our field trip: They don't always grow in damp and shady places on the forest floor. In fact, they can grow in places where the casual observer is least likely to expect to find them — in this case on bare, dripping wet rock exposed to direct sunlight and cool temperatures, especially in winter, at 5,500 feet.

During the day-long field trip, I also learned many other fascinating facts about the extraordinary group of plants called mosses. They are among the oldest and most diverse plants on the planet. The oldest fossils attributed to bryophytes — mosses, liverworts and hornworts — date to the Upper Devonian (about 350 million years before present or MYBP). Wyatt put that in perspective: "But most believe they diverged from green algae even earlier, perhaps 500 MYBP. They are also the second-most diverse group of land plants, after the angiosperms, with an estimated 15,000 mosses, 9,000 liverworts and 100 hornworts — or about 25,000 total species.They are more diverse than ferns and fern allies and greatly surpass the gymnosperms in number."

With that as a backdrop, here's a sampling of what else I learned about mosses on my trip.

What's in a name

On a moss walk, you get much more than mosses. The goal is to see mosses — and you will, plenty of them. But moss specialists and enthusiasts are interested in other plants, too. Wyatt and Stoneburner took plenty of time to point out many of the interesting plants on our hikes. Those included shrubs such as bush honeysuckle (Diervilla sessilifolia), high bush blueberry (Vaccinum corymbosum), Catawba rhododendron (Rhododendron catawbiense) and witch hobble (Viburnum lantanoides); flowering perennials such as blue bead lily (Clintonia borealis), green-headed coneflower (Rudbeckia lacinata) and Turk's-cap lily (Lilium superbum); ferns such as fancy fern (Dryopteris intermedia), Southern lady fern (Athyrium Filix-femina) and hay-scented fern (Dennstaedtia punctilobula); numerous tree species, including the two most prominent in the western North Carolina range of the Appalachian Mountains, red spruce (Picea rubens) and Fraser fir (Abies fraseri), plus numerous grasses, carexes and other plants.

Most mosses don't have common names, but some do. "Most mosses are like a separate world, even to botanists," conceded Wyatt. That's because mosses are so small and so seldom dominant in most plant communities that they tend to be ignored by most botanists, he explained.

It was like being in an outdoor classroom as he and Stoneburner described almost all the mosses we saw by their scientific names, a combination of the genus and species. One group was the "feather" mosses, a set of common and widespread species in spruce-fir forests that can grow on soil, trees and even rocks and receive their name from their branching habit, which gives the appearance of a bird feather. That's a lot easier to remember than the names of the five feather mosses we saw: Hylocomium splendens, Hylocomium brevirostre, Rhytidiadelphus triquetrus, Ptilium castra-castrensis and Pleurozium schreberi.

Other mosses with common names included star moss, so-called because the leaves look like star bursts when viewed from the end of their stems; fern moss, which looks like a miniature fern; haircap moss, which gets its name from the structure covering the spore capsule, which is woolly and looks like a cap; and the palm tree moss, which has a terminal rosette of leaves, making it look like a miniature palm.

Scientific names for mosses don't have a Linnaean lineage. "The scientific names for flowering plants go back to Linnaeus in 1753," said Wyatt, adding that "Linnaeus was not an expert of non-vascular plants." Therefore, he explained, "the scientific names of mosses go back to Johann Hedwig and a publication on mosses published posthumously in 1801." At Grassy Ridge (milepost 436.8, elevation 5,250 feet), we found a moss named after Hedwig, Hedwigia ciliata. Interestingly, you find this moss, Wyatt said, growing on granite outcrops in the Piedmont, where it is always associated with Sedum pusillum, an endangered species of sedum, or stonecrop.

Don't try to remember all the scientific names you'll hear — unless you are a botany student. In the case of mosses, botanists don't have much choice as most mosses lack common names. Some of the Latin names are true tongue twisters, and you'll hear so much Latin that if you try to remember it all, by the end of the day your head may explode! Besides, field-trip leaders don't expect you to remember all the botanical names. They just want you to enjoy the walk and learn the basics.

Some plants called mosses aren't mosses. One example is reindeer moss (Cladonia rangiferina), which is a small-growing, clump-forming lichen found in great abundance in the Arctic where it's a food source for reindeer. It has worked its way down the spine of the Appalachians. Wyatt and Stoneburner have published a paper extending its range as far south as granite outcrops in Alabama and Georgia. We saw unusually large clumps of it at Waterrock Knob/Yellow Face at milepost 451.2. At 6,292 feet, this is the 16th highest mountain in the eastern United States. Another example are the club mosses, or Lycopodium, which are vascular plants related to ferns. The common name comes from the club-like shape of the sporangia (strobili). A third example is Spanish moss (Tillandsia usneoides), which not only isn't a moss, it isn't even Spanish! The long, dangling and gray epiphytic flowering plant is in the bromeliad family and can often be seen in the southern United States on cypress and oak trees from Florida to Texas.

Why mosses are so small

Mosses are in a group of plants commonly called bryophytes, which also includes liverworts and hornworts, that have no vascular tissue, which limits their size. Most of the plants that come to mind, said Wyatt, are vascular plants. This includes flowering perennials and annuals, grasses and flowering shrubs and trees, conifers, cycads and ginkgos and ferns. All these have vascular tissues that perform transport functions critical to plant growth: xylem for conducting water and phloem for conducting sugars. If you're ever on a plant walk and hear some of these words and think they sound vaguely familiar, look around at the rest of the group. Many of them are probably silently thinking the same thing you are. Now I know why my ninth-grade biology teacher said to pay attention in class — you might find this information useful some day! The largest moss in the world, Wyatt noted, is Dawsonia superba. It's found in the Blue Mountains of southeastern Australia and, while small at maturity relative to most vascular plants, it can reach heights of over two feet.

Mosses don't have predators. "Nothing much feeds on them," said Stoneburner. But, she pointed out, they serve the animal kingdom in other, less well-known ways. "They have small invertebrates that live in them, nest in them and use them for their hunting grounds," such things as water bears, slugs, crane flies and Bryobia beetles. And many species of birds line their nests with moss.

Mosses are not invasive. In fact, said Stoneburner, if you try to have a moss lawn you will constantly be fighting a battle to pull herbs and grasses out of your moss bed because their seeds settle in, sprout and the seedlings will thrive in the moss mat (just like on the rock face at Wolf Mountain). An example of that, she said, occurs in the Southern Appalachians. Mosses in some cases will cover fallen trees so extensively that the trees are called nurse logs. They get that name because the seeds of spruce, fir and birch fall onto the moss beds covering the logs, sprout in the damp environment of the moss and establish new trees. The same thing happens to a different extent in moss gardens in the landscape.

Beneficial for your garden

There are some good reasons to garden with moss. Some of those are are: to cover bare soil (Atrichum); prevent erosion (Bryoandersonia); add nutrients to the soil (Leucodon and Anomodon); provide habitats for invertebrates (Leucobryum, Dicranum and Polytrichum); and provide nesting material for birds and habitat for salamanders and frogs (Plagiomnium).

Mosses can be a victim of their own natural beauty. We passed so many nurse logs on the first part of the path at Waterrock Knob that the area resembled what hikers might expect to see in the Pacific Northwest. The moss doesn't root in these logs, and that sometimes results in one of the saddest things that happens in these mountains, Stoneburner said. "Poachers roll up and remove mosses from logs, or strip them from slopes to sell to boutiques where they are used to wrap baskets or various articles for sale to buyers unaware of their provenance."

Mosses have a lot of amazing characteristics. Mosses are very drought resistant and can seemingly come back from the dead. "We could leave a moss on the counter for a couple of weeks, or even put it in a special envelope, which is what they do in herbaria, wet it up, stick it under a strong light and it would start photosynthesizing again," said Stoneburner. "They are really well known for their capacity to withstand extreme desiccation and still, even after several years, resume growth."

Poikilohydric is the term for this characteristic, and it refers to plants that can't regulate water loss internally and, as a result, respond to the amount of water available in the environment at any given time. This gives them the ability to outdo even the resurrection fern by resuming maximum photosynthesis within 15 minutes of rehydration, said Wyatt.

Interestingly, mosses don't grow in saltwater environments. "For whatever reason, they simply cannot tolerate salt," said Wyatt. "There are numerous vascular plants that have a variety of means of excluding salt at the roots or excreting salt from special glands on the leaves. It may be that these adaptations require vascular tissue to be effective."

Difference between mosses and other small non-vascular plants

Observe closely on your walks and hikes and with a good field guide and practice, Stoneburner said, it will become easy to recognize differences among the major groups, or the mosses, liverworts, hornworts and lichens. She compared this to telling the differences between a flowering tree and a conifer. Once you become familiar with the groups, you'll begin to recognize common species.

Mosses have some really neat bryophyte relatives. If you're observant, you'll recognize liverworts and hornworts on your walk (we saw plenty of the former, none of the latter), and your field companions will no doubt point them out and ask about them. These denizens of the forest are just too interesting to pass by.

To the untrained eye, many mosses may look alike. To botanists and taxonomists, so-called look-a-likes can be quite different. "At higher levels of the classification, diploid sporophyte characters are important," said Wyatt. "Within a genus most species are distinguished by leaf and stem characters of the dominant haploid gametophytes. Evidence from studies employing genetic markers from DNA shows that many moss species, despite seemingly minor differences in leaf shape, margins or midribs, are more strongly differentiated than typical flowering plant species."

There is a best time to see mosses and other bryophytes. "It's in the winter in the Southeast, after the leaves have fallen from the trees," said Stoneburner. They grow a lot then, and usually they are the brightest green element in the forest. "Robert used to joke that in the summer he could study the flowering plants, and in the winter he could study the mosses because they really like the sunlight!"

"My plants were sleeping!" exclaimed Wyatt. A good place to look for mosses, he added, are the north-facing slopes of new road cuts. "A lot of people say lichens are the first to come in, but, really, it's mosses."

Mosses are very important ecologically. Sphagnum peat bogs are important as a carbon sink, harboring an estimated 550 gigatons of carbon. Sphagnum is a major reason that peat bogs are acidic. North America has 40 percent of the world's peatlands, amounting to 1,735,000 square kilometers.

How moss reproduces

Most mosses are unisexual, with separate green, leafy male and female plants, that as in animals, produce sperm and eggs. This is in contrast to most flowering plants, which are bisexual or hermaphroditic. The result of sexual reproduction that occurs in the leafy green plants is a stalk with a capsule that rises above the leafy, green plant and remains attached to it. It is in the capsule that spores are produced that are typically wind dispersed and travel great distances. Many of the boreal feather mosses seen at high elevation in the Southern Appalachians also can be found at lower elevations in Scandinavia, for example. When ripe, sphagnum moss capsules can burst with such force that some claim to hear them pop.

Mosses can also spread asexually. One way you can spread mosses is by simply tearing off some pieces and rubbing them together in your hand and then literally scattering the tiny pieces to the wind. Each little piece of the moss stem or leaf can grow into a new moss if it finds a favorable spot.

There are certain tools you should take on a moss walk. They include: a field guide (if you are on the East Coast, "Common Mosses of the Northeast and Appalachians" is an excellent choice); 10x and 20x hand lenses for seeing finer features that are difficult to see with the naked eye, such as teeth on the leaf margins, and on which identification can sometimes depend; clear plastic baggies to collect specimens; a walking stick; bottled water; bug spray; and a backpack to store various items (a fly fishing vest has many pockets and will also work, but it can get hot on a summer walk). Be aware that collecting plants is not permitted on U.S. Forest Service lands, and be sure to ask permission to collect before hiking on private property.

And, finally, I found out that one of the first things I learned about mosses turns out to be a myth. If you get lost in the woods, don't look for moss on the north side of a tree thinking it will help you find your way home. "That's a myth," chuckled Wyatt. "Don't rely on that!"

"Moss can circle a tree," said Stoneburner, adding that "if you try to find your way out of the woods by looking for moss on the north side of a tree, you just may find yourself going in circles!"