What's so interesting about mosses? For one thing, there are so many kinds of them (about a hundred species in an average U.S. county) that it's always fun to see how many of them you can place on your Moss Life List. Also, mosses display such amazing adaptations and variations in form and niche preference that it's just a blast to wrap your brain around them! At first glance, mosses are all alike. At second glance, they make a whole new world to explore.
Mosses are very small green plants. A typical one is drawn at the right. The stem may not be much thicker than a thick hair, and normally is densely covered with leaves maybe 1/16th or 1/8th of an inch long. Often moss stems branch and rebranch. Often many mosses grow together forming a thick green carpet. Sometimes this carpet is no larger than a thumbnail, but other times it may cover areas several feet in diameter.
There is a good chance you might spot some mosses in your own backyard, even if your backyard lies smack inside a big city. If an old rock fence or some big trees grace your yard, your chances are very good. Even if all you have is a house and a lawn there is still a fair chance you can find some.
When looking for mosses, remember that most, but not all, moss species like moist, shaded places. In the woods they're on old fallen logs and shaded rocks. Around the house, look beneath dense shrubbery, on the northern sides of tree trunks, and at the base of the house's northern foundation. Why north? Because in the Northern Hemisphere drying-out sunlight doesn't shine on north-facing surfaces.
When you look for mosses, be sure to think small, and take along your hand lens. Most backyard mosses are less than an inch high, and often much smaller, though in rainforests and cloudforests they sometimes grow much larger. Unfortunately, mosses are pretty sensitive to air pollution so if your town's air is lousy you may be out of luck.
If you get interested in mosses and acquire a moss field-guide, the first thing you should do is to check out the pages showing moss structure. In the drawing at the right, notice that the moss reproductive part consists mainly of a capsule (the operculum, annulus, peristome and urn) on a seta, or stalk. Capsules and stalks appear only during part of the year. In the color picture above the capsules are the green pod-like things at the very top and the stalks are the maroon-colored stems connecting the capsule above with the green moss plant below. During much of the year most mosses consist of only the green plant, with the stalk and capsule appearing only when conditions are right for reproducing.
When identifying mosses you almost always need mature capsules, for details of stalk and capsule structure vary endlessly and are important in moss identification. A capsule's minute peristome, annulus, operculum, and calyptra vary as markedly from species to species as do flower parts from one flowering species to another. The shape and arrangement of individual cells in moss leaves are also important in moss identification.
Since all these features are minuscule, here is one inescapable fact about the process of learning your neighborhood mosses:
To identify mosses, you nearly always need a hand lens,
and very often a microscope.
The microscopic view of a leaf of the moss Ptychomitrium serratum shown below reveals features that are hard to see with the naked eye but which are very important for identification. For example, the leaf margines bear spiny teeth; a midrib or "costa" runds down the leaf's middle, and; cells are all more or less the same size, despite cells of many mosses being much longer along the margins.
Even if you've mastered identifying other kinds of plants, once you begin studying the mosses' incredibly variable microscopic details, you'll be confronted with forms, shapes, and concepts unlike anything you've run into before. For example, right now I glance into my moss identification-key and the first sentence I see reads, "Capsule raised on a pseudopodium, spherical, black, shedding lid explosively."
The Flora of North America provides identification keys & descriptions to moss genera & species in the following moss families:
Of course, these new terms can be handled the same way we tackle all other groups of organisms, by "leapfrogging." When you run into an unknown term, leapfrog to a definition in the field guide's glossary. Then keep leapfrogging from definition to definition until it all comes together, maybe days or months later...
Once you've identified the moss species around your own home, then it becomes a real thrill to range farther afield into new habitats where you can find species you've never seen before. Some moss species grow only on outcrops of granite; others only in water-saturated soil; others only on rotting wood; others only on bare soil; etc.
One reason mosses make good subjects to specialize in is that they can be easily collected and preserved. Just pick one up, blot it dry, and plop it into an envelope on which you've written the appropriate where's and when's. Collecting plants larger than mosses can turn into a logistical nightmare, especially because usually they must be dried to keep from rotting or becoming moldy.
Elsewhere we say that gymnosperms evolved before plants with real flowers and fruits came along. In the same way we can say that mosses came into existence before flowering plants and gymnosperms. The first flowering plants appeared about 135 million years ago. Conifers were on the scene far earlier, about 285 million years ago. Well, the first mosses seem to have come into existence way before either of these, some 350 million years ago, before dinosaurs, before all reptiles and even before flying insects!
Of course, this was long before flowers appeared, so mosses reproduce with spores. Despite spores being such primitive items, they do have certain advantages. For instance, spores are so lightweight that wind can carry them for immense distances. However, precisely because of their tiny sizes, spores can't carry much stored food for "baby moss" (called protonemas) to live on, and that's one thing a germinating bean does have.
This means that when moss spores germinate they must be in practically ideal surroundings if they are to gain a foothold in their environment and survive. Temperature, moisture, soil pH, and many other factors must all be congenial to the protonema, or else it will die, or the spore won't germinate in the first place. A sprouting bean, on the other hand, if it doesn't find appropriate conditions, can survive at least a little while using food stored in its cotyledons, and maybe conditions will change. Maybe it'll rain, or cool off.. This problem of spores being unable to carry much energy for the emerging protonema is one reason why even if a moss produces a million spores, it'll be lucky if just one spore eventually produces a mature plant.
On the Web, check out these sites:
To review moss-oriented books available at Amazon.com in both the USA and the UK, click here.