Get ready! I’m about to attempt to convince you that MOSSES ARE AMAZING! We tend to look past these ancient, tiny plants on trees, rocks or bare soil or we try to thwart them on roofs or walls. But really, once you spend a few minutes learning about these little plants, well, maybe you’ll be as fascinated as I am!

It all started with a “moss walk” that my friend Aaron Carroll and I took at Waterloo Recreation Area with Dr. Jeremy Hartsock, a professor at Michigan State University. We followed a shady path on a May morning, through a moist forest dissected by a wandering creek, then arrived at a very large bog. What a place! Native woodland flowers were blooming, with great patches of Trillium and blooming shrubs of High Bush Blueberry everywhere. And the forest floor was rich with over twenty different species of moss.

We were each given a magnifying loupe to look closely at the stems and leaves of these miniature plants and we couldn’t believe the variety. And along the way, Dr. Hartsock kept explaining the history and lives of mosses.

Aaron and I got so intrigued by the mosses themselves that we neglected to take any photos of the forest and bog! Our apologies. But at least I can share with you what we learned from Dr. Hartsock and from an award-winning book that he recommended, Gathering Moss: A Natural and Cultural History of Mosses, by Robin Wall Kimmerer.

We thank Dr. Hartsock for his generous willingness to verify our moss species and to answer other questions that arose as we developed this blog. And my thanks to Aaron Carroll for providing his amazing closeup photos and even a video of some wildlife within in a moss, as well as sharing my enthusiasm for learning about these ancient, intriguing plants. And a last thanks to Dr. Ben VanderWeide who patiently helped me understand the complexities of moss reproduction!

Note: According to Professor Kimmerer: “…mosses don’t usually have common names for no one has bothered with them. They have only scientific names, conferred with legalistic formality according to the protocol set by Carolus Linnaeus, the great plant taxonomist. Even his own name, Carl Linne, the name his Swedish mother had given him, was Latinized in the interest of science.” So have fun with these tongue-twisting names! Also, even though mosses live across the face of the earth, in all kinds of habitats, I will be concentrating on woodland mosses which appear in our parks here in southeast Michigan.

Mosses Inhabit Their Own Strange World Even While Sharing Ours!

Mosses breathed out some of the first oxygen on earth. Algae may have kick-started life on earth by photosynthesizing with sunlight, carbon dioxide and water in ancient seas. But mosses were the first to do it on land. That was about 350- 400 million years ago. The byproduct of their photosynthesis, of course, is oxygen which made all of us humans and many other earth creatures possible! As Wikipedia defines it, “Most photosynthetic organisms … are able to synthesize food directly from carbon dioxide and water using energy from light.” But the way these ancient mosses assemble those three ingredients for photosynthesis – sunlight, water and carbon – is quite different from other plants.

Mosses and Sunlight

Mosses make a plus out of being tiny, shaded plants. Kimmerer explains, “One consequence of being small is that competing for sunlight is simply not possible – the trees will always win. So mosses are usually limited to life in the shade, and they flourish there. The type of chlorophyll in their leaves differs from their sun-loving counterparts, and is fine-tuned to absorb the wavelengths of light that filter through the forest canopy.”

Mosses and Water

Mosses, the most primitive of plants, can’t conduct water from the soil to the leaves. They don’t have roots, for example; they just use small hair-like rhizoids to cling to surfaces. They don’t have vascular systems that can conduct water up from the soil to the leaves like other plants do.

So mosses specialize in preserving the precious water in the air around them, mists from waterfalls, the rain dripping through the forest canopy or the water flowing to and through them as it’s funneled down the bark of a tree. Moss leaves curl to hold or channel water. Their surfaces are dense with tiny leaves which have minute bumps and ridges creating tiny pockets of water. Here’s a photo taken by my friend Aaron through a microscope of the surface of a leaf of Plagiomnium cuspidatum.

Being small also keeps many mosses closer to the ground where the air touches the earth, creating what is called the “boundary layer.” The air which we breathe several feet up from the ground is turbulent as it encounters friction with taller plants and creatures like us walkers! But it slows down as it nears the ground and sometimes is completely still. Sun and water, trapped near the ground in still air, produce humidity that can be absorbed through the moss leaves, the very moisture that mosses require for photosynthesis, growth and reproduction. Kimmerer writes, “Even when the temperature is below freezing, the mosses on a sunlit rock may be bathed in liquid water.” And you can see in the photo below that the moss is green and thriving on a snowy rock on a January day at Bear Creek Nature Park.

When mosses do dry out or even experience long droughts, they revive shortly after water returns. Their cells store enzymes for cell repair. Mosses are tough little survivors!

Mosses and Carbon Dioxide

Mosses near the forest floor, down in that boundary layer, benefit from the presence of decomposers, like fungi (mushrooms), bacteria and other microorganisms. When an old log or leaf litter decomposes, the carbon dioxide released in the process is absorbed by the moss through its tiny leaves. In fact, according to Professor Kimmerer, the carbon dioxide within the boundary layer near the soil surface may be ten times the amount in the air we hikers are breathing as we walk through the forest! That partly explains why mosses can store a significant amount of carbon.

The Challenges of Producing Moss Offspring…and Yet They Succeed!

Mosses had to evolve quite a bag of tricks in order to reproduce! After all, they don’t produce seeds that can be carried off by wind, water and wildlife like flowering plants. What to do? Well, most mosses can clone, spreading genetically identical copies of themselves. Many can regenerate from just a small piece of themselves. Others produce gemmae, modified tissue that can detach from its parent and transform into an identical plant. But cloning didn’t produce the diversity of moss species we see today.

All plant species, including mosses, trees and garden flowers, go through a two stage cycle, which botanists call “the alternation of generations.” In flowering plants, most of this two stage process is going on unseen within the blossom.

In mosses, it’s right there before your eyes! The most conspicuous stage of mosses is called the gametophyte generation. When you’re looking at moss on the trees or lushly spreading in carpets on the forest floor, you are looking at whole bunch of gametophytes.

The moss/gametophyte forms stems with leaf-like appendages (which I refer to here as “leaves”) that can photosynthesize; they create the energy for the whole process. The gametophyte has only one set of chromosomes yet oddly, it can produce the two different reproductive elements required for sexual reproduction, the sperm and the egg (also known as male and female gametes).

At the tip of one moss stem, the gametophyte (the moss plant) produces a cluster of leaves that conceals the moss’s female egg-producing structure (the archegonium). It also stores enough water to keep the egg moist and to allow sperm to swim to the egg.

On a different stem, a gametophyte produces a tuft of leaves that forms the moss’s male sperm-producing structure (the antheridium). It holds a cluster of green sacs (antheridia) containing sperm.

But how does the moss sperm swim to the the egg if they’re in two different places on the moss? No bees, no butterflies, no wind are around to help them out. Well, you guessed it. Water seems to always be the go-to solution for mosses.

Many moss species use absorbed water to eject the sperm from the male structure (antheridium). “When the sperm are ready to be released, the antheridium absorbs excess water, swelling until it bursts,” says Kimmerer. Sperm shoot out and along with the sperm comes a surfactant that makes the water less viscous and easier for sperm to swim in. The sperm rarely travel more than four inches from the antheridium!

Stems of some species produce a “splash cup,” a flat disk of leaves with bright green sperm sacs arranged like little petals or sausages around the disk. We were delighted to discover some peeking out around the edges of a reddish-brown disk on this Atrichum moss after Aaron took the photo below. When hit by a falling rain drop, mature sperm splashes out a hefty 10 inches, a long distance for a moss!

However it emerges, the sperm needs a continuous film of water from rain or mist near a waterfall to wash over the moss, carrying the swimming sperm toward the eggs “like surfers on a wave,” as Kimmerer so charmingly puts it! The vast majority of these “surfers,” though, get lost in the moss leaves or dry up when the water evaporates. Only a tiny percentage of sperm find their way to an egg.

The lucky egg found by the swimming sperm grows into a sporophyte like the ones you see in the photo below. Anchored in the moss, the sporophyte grows a long stem with a capsule at the end, a stem just long enough to rise gracefully above the boundary layer where the air is beginning to move. Inside the capsule, spores form by a process called meiosis.

(Are you still with me here? Such an arduous task for moss to multiply – but it’s kept working for hundreds of millions of years, so who am I to criticize, right?)

When the spores mature, the lid of the sporophyte capsule opens and the spores are dispersed in a powder-like cloud. Spores that land in the right spot will germinate and grow into a new generation of gametophyte moss, which will eventually produce more sporophytes. The cycle is complete ! Whew! We made it!

How Important Are Mosses, Though…?

Really important! Many insects lay their eggs in mosses to protect them from predation. In my short video below taken at Lost Lake Nature Park, a female Crane Fly (genus Tipuloidea) danced above patches of moss as she laid her eggs in the soft, green moss. And as readers of this blog know, insect larvae are the essential baby food for birds, adult birds and many other creatures. They have a crucial role to play in any any food web. (Press play to watch the video.)

By absorbing water and nutrients directly from the air through their leaves, moss absorb pollutants. Growing on bare rock, they can capture organic material like dead leaves, dust, fallen insects, etc., which later enrich the soil. They create a living mat on bare soil which prevents erosion from water or wind. Many birds, chipmunks, flying squirrels and other creatures line their nests with moss cushions to protect their eggs. Flowers, ferns and even tree seedlings often get their start when a fertilized seed or spore falls into a patch of moss and is nurtured by the moisture and protection of moss. Here’s a small sample of the plants that I’ve seen rising from moss over the years:

Some research has shown that the density of mycorrhizae, the thread-like web of fungi that nourish tree roots, increases when under a layer of moss. And Sphagnum moss (genus Sphagnum) is famous for storing carbon. By accumulating in layers year after year and decaying slowing in an oxygen-poor environment, it creates large depths of peat below the surface of a bog. On our moss walk, Dr. Hartsock assembled the bouquet below to show the walk participants the color variety and amazing structure of sphagnum. We were told to only remove tiny amounts of any moss that we wanted to identify with our magnifying loupes. Mosses grow slowly and mining them for “peat moss” soil amendments or potting soil, for example, can affect the health of the whole bog ecosystem.

A Closer Look at Three Common Mosses

My friend Aaron carefully used magnifying extensions to his camera lens to get even closer to three mosses than we could with the loupe. Watch how these mosses become more complex and detailed in the three slideshows below. Each begins with a shot to show the moss’s location at Bear Creek Nature Park and then goes from 1x to 3x to 10x magnification with sometimes a leaf closeup as well. It’s pretty cool. The identifications were kindly verified by Dr. Hartsock after seeing Aaron’s photos. He was as impressed with them as I was!

Atrichum genus, but what species? Maybe angustatum

Dr. Hartsock told us that identifying a specific species within the genus Atrichum is not always possible in the field. The differences between them can only really be verified in cross-section under a powerful microscope. His strong guess is that the species in Aaron’s photos is Atrichum angustatum, but it could be one of two other species, A. altecristatum or A. crispulum. So here’s the first short slideshow.

Plagiomnium cuspidatum Slideshow

Plagiomnium cuspidatum has two forms, trailing vines with leaves neatly in two rows and stems with capsules standing upright.

Thuidium delicatulum Slideshow

Thuidium delicatulum grows on damp, shady forest soil, rotting logs and rocks. It looks like miniature ferns until you get really close. You can almost sing that moss’ name!

“Taking a Walk” Through A Minuscule Moss Forest

I’m fascinated by the world in which mosses abide, so foreign, so strange. Imagine! The still or slowly moving air that surrounds them in the boundary layer – warm, humid, dense with carbon dioxide – is so radically different from ours up here in moving air with lots of sunlight, wind and oxygen! And it exists right at our feet or on a nearby tree, or between the cracks in the sidewalk!

Kimmerer describes what she can see in the tiny forests of a moss when looking through a stereomicroscope which can show more three-dimensional images. I’ll let her words describe what’s moving down there – predators, prey, and all – through a comparison she makes between a visit to a Ecuadorian tropical rainforest and a tiny moss forest :

“…A good stereomicroscope…lets you go wandering at will through a living moss turf, like bushwhacking through a jungle. Tiny needle in hand, like a machete to make a path …I’ve spent hours lost in threading my way between the stems, bending low beneath a branch and turning over leaves to see what’s underneath…While the height of the moss mat is approximately three thousand times smaller than that of the rain forest, they nonetheless exhibit the same kind of structure, the same kind of function…One gram of moss from the forest floor, a piece about the size of a muffin, would harbor 150,000 protozoa, 132,000 tardigrades, 3000 springtails, 800 rotifers, 500 nematodes, 400 mites and 200 fly larvae.” She describes the sights. “The interior of a moss clump can be heavily colonized by algae, making it look like a moss-draped rain forest in miniature. Golden disks of single-celled algae rest among the moss leaves.” “Predaceous larvae lie like snakes in the branches.” She describes the microscopic “water bear” or tardigrade (phylum Tardigrada) as it wanders in its moss forest, “Nosing through the foliage, trundling along on eight stumpy legs, the water bear bears a remarkable likeness to a tiny polar bear.”

Aaron and I would love to see a water bear that “clings by long black claws to the moss stems.” Tardigrades can desiccate along with moss, shrink, be blown about like bits of dust, and then revive as soon as they are touched by water. Wow!

But imagine my surprise when Aaron did manage to get a 10 second video through the microscope (!) of a creature within moss! He took a sample of moss from a tree in his yard and got some of the water from it under the microscope. And behold, what appears to be a rotifer (phylum Rotifera), a microscopic, multicellular animal motoring about with two coronas of cilia on its head! The whirling hair-like cilia draw water into the rotifer’s mouth where it sifts out the food and chews it with tiny jaws! I can’t verify it genus, species or even its phylum, really, but I did find a University of California Berkeley website with a photo of a rotifer very much like Aaron’s and Kimmerer tells us that over 800 of them can be in a gram of moss – so I’m happy with our first sighting! (Click on the video to see those coronas spinning!0

Aaron and I still hope that we’ll someday have a more powerful stereoscopic telescope with which we can take a walk through the moss with a needle, like Kimmerer. But for now, I’m just content to know that this amazing habitat exists in my world, a habitat I never seriously noticed until now. I hope I’ve shared some of my surprise and delight with you, too.