The Minimalist Genius of Moss
June 10, 2017 | Posted in: Science
“Moss is inconceivably strong. Moss eats stone; scarcely anything, in return, eats moss. Moss dines upon boulders, slowly but devastatingly, in a meal that lasts for centuries. Given enough time, a colony of moss can turn a cliff into gravel, and turn that gravel into topsoil.” Gilbert
Humans are often a hierarchically minded species. We imagine that life is one big pecking order: small and simple ones on the bottom, large and complex ones on the top, and the topper of them all, why it’s us, naturally. In this anthropocentric view, moss is certainly near the bottom. Lost to the cracks, roots of trees, shadowed rock faces, moss is the settler of shady nooks and crannies, hidden in plain sight, carpeting surfaces all around the globe, including the arctic poles. They live where no other plants seek to live, creating homes on seemingly inhospitable, soilless surfaces.
“So what is a moss? A true moss or bryophyte is the most primitive of land plants. Mosses are often described by what they lack, in comparison to the more familiar higher plants. They lack flowers, fruits, and seeds and have no roots. They have no vascular system, no xylem and phloem to conduct water internally. They are the most simple of plants, and in their simplicity, elegant. With just a few rudimentary components of stem and leaf, evolution has produced some 22,000 species of moss worldwide. Each one is a variation on a theme, a unique creation designed for success in tiny niches in virtually every ecosystem.” Robin Wall Kimmerer, Gathering Moss
Moss is labeled primitive, in the sense that it hasn’t changed much since its ancestors crawled out of the ocean to first colonize land 350 millions years ago. At that time however, mosses were on the forefront of evolution, devising a way to reproduce in an airy world rather than an aquatic one. The ocean dwelling predecessors to plants could simply release their eggs into the surrounding water. But on land, eggs had to be nestled safely within the female parts of the moss to avoid drying to a crisp. Examine any modern plant and you’ll see this same egg-preserving strategy at work, all directly stemming from the evolution of mosses.
While most other plants and animals collect and move the water in their bodies using complex plumbing, valves and glands, kidneys and vessels, mosses have molded their form to water. Water has its own laws of movement: it likes to stick to itself and it likes to stick to surfaces. The leaves of mosses grow to collect and convey the flow of water through its body without using any of its own energy. In a brilliant minimalistic approach, mosses simply grow to create paths and pools in accordance with waters’ natural movements.
Water is necessary for moss to procreate, photosynthesize, and grow. But lack of water isn’t necessarily death to a moss. Most plants need to maintain a steady amount of water to remain healthy, and they die quickly when water drops below that level. Mosses on the other hand, with their simplicity, are survivalists:
“Mosses may lose up to 98 percent of their moisture, and still survive to restore themselves when water is replenished. Even after forty years of dehydration in a musty specimen cabinet, mosses have been fully revived after a dunk in a Petri dish… All signs of life are extinguished when they are dry: no movement, no gas exchange, no metabolism… a state know as anabiosis, or lack of life. And yet, as soon as water is returned, life suddenly is renewed. Their apparent death, followed by resuscitation, suggested that life might be stopped and then re-started.” Kimmerer
Mosses die only to return to life, and they can live for a very long time. The elegant simplicity of their bodies and their ability to clone themselves allows them to cheat death itself, for a heroic chunk of time anyways. One Antarctic moss on Elephant Island has been growing for 5,500 years now, and a younger nearby moss neighbor on the island of South Georgia is 2,200 years old.
“And there, rising no more than an inch above the surface of the boulder, she saw a great and tiny forest… Here were rich, abundant valleys filled with tiny trees of braided mermaid hair and minuscule, tangled vines. Here were barely visible tributaries running through that jungle, and here was a miniature ocean in a depression in the center of the boulder, where all the water pooled… Just across this ocean… another continent of moss altogether. On this new continent, everything was different… Here, the moss grew in mountain ranges the length of Alma’s arms, in elegant, pine tree-shaped clusters of darker, more somber green… She felt herself growing breathless. This was the entire world. This was bigger than a world. This was the firmament of the universe, as seen through one of William Herschel’s mighty telescopes. This was planetary and vast…” Elizabeth Gilbert, The Signature of All Things
If you zoom into the world of moss with a magnifier you discover that these little green pads are actually a forest, dense and humid, bursting with life. “One gram of moss from the forest floor, a piece about the size of a muffin, would harbor 150,000 protozoa, 132,000 tardigrades, 3,000 springtails, 800 rotifers, 500 nematodes, 400 mites, and 200 fly larvae.” (Kimmerer). Prey and predator evolve together in these minuscule habitats just as they do in the jungles and forests we humans can walk through.
Like forests of trees, moss creates its own microclimate, slowing the air above it, keeping it warmer and more moist. This is known as the boundary layer, a biologically maintained meeting of air and land, cultivated for the mosses comfort. This mossy ecosystem not only nurtures its own ecological community, it aids in the growth of forests of trees as well, acting as a nursery to seedlings. A tree’s seed that falls in a moss mat finds a much easier start to life, protected from the elements and held in the moist embrace of mosses’ minuscule leaves.
For some species of moss, this protective boundary layer does cause some trouble when it comes to reproducing. That layer of still air makes it hard to send out spores: small little amber spheres ready to catch the wind and hopefully land in a suitable location to transform into the next generation of moss. To overcome this barrier, the moss grows a long stalk (called a setae) with the spores on its crown, and thrusts it up beyond the boundary layer and into the turbulence of air vortices above, where the amber spores are sucked out of their capsules and whirled away. The odds of landing in a moist and welcoming habitat aren’t good, but for the lucky spores, a safe and hospitable landing will allow them to soak up the moisture needed to send out green threads which will spread and create the groundwork for future growth.
“Mosses do exhibit the entire range of reproductive behaviors from uninhibited sexual frenzy to puritanical abstention. There are sexually active species churning out millions of offspring at a time and celibate species in which sexual reproduction has never been observed. Transexuality is not unheard of; some species alter their gender quite freely… Sex is not the only opportunity for propagating themselves. Long before the advent of biotechnology, mosses have been making clones, saturating the environment with genetically identical copies of themselves… A single leaf, broken off by accident and lying on moist soil, can produce an entire new plant.” Kimmerer
Returning from death after decades, growing for millennium, first colonizing land, patiently grinding down rocks, evolving cloning, creating teeming moss-forest ecosystems: moss has done all this with a simplicity of biology and a smallness of size that makes most people completely overlook it. But if we pay attention, mosses have important information for our own health: despite their general durability, they are very susceptible to air pollution. If you live in a neighborhood devoid of mosses, it very likely means your air is harmful to life, your own included. So, break out the magnifying glass and remember: even the simplest and smallest lifeforms are wonders unto themselves.
The following books informed this post:
Gathering Moss: A Natural and Cultural History of Mosses, Robin Wall Kimmerer
The Signature of All Things, Elizabeth Gilbert
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