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Getting to know you: A new field guide to mosses

April 23, 2014

Peat mosses, also known as sphagnums, are mop-topped, wetlands-loving plants of distinctive form.

Nearly 10 years ago, Karl B. McKnight, a biology professor at Saint Lawrence University in very upstate New York, came face-to-face with one of the most fundamental problems in all of science. McKnight had wanted to study some basic questions about why organisms are rare or common, and he thought he’d found the perfect test subject: mosses. In his outdoor laboratory, the 800-plus-acre Glenmeal State Park close to the Canton, N.Y., campus, these ancient plants, which evolved from filamentous green algae more than 350 million years ago, were ubiquitous and diverse. But in examining the “forests of Lilliput,” to use a perfect description from the title of John Bland’s classic book on these plants, McKnight realized something horrible.

“We didn’t know the names of any of the mosses, and there was no easy way to learn them,” the researcher told me during a phone interview. “Clearly, we couldn’t do ecology until we’d paid our dues in moss taxonomy and systematics, and that was going to take some time and effort.”

Lots of time and effort.

The standard guide, “Mosses of Eastern North America,” is a 1981, two-volume set by botanists Howard Crum and Lewis Anderson, and while it was considered the Bible of Bryology—the study of mosses—working with the 1,330-page-long tome was akin to reading the Bible in Aramaic when your first and only language was English. But McKnight is a dedicated naturalist and an environmental omnivore.

“I’ve spent years learning sedges, grasses, trees, wildflowers, birds, salamanders, frogs… all of creation,” he said.
Mosses were just another missing piece of the puzzle, and so he and his students took on the bryophyte learning curve.

Last year, a truly monumental effort came to fruition with the publication of “Common Mosses of the Northeast and Appalachians,” an engaging and eye-catching field guide from the Princeton University Press. I’ve mentioned the guide in earlier editions of the Journal, and I had hoped to write about it at length in 2013. Alas, those plans had to be shelved when the drought arrived last spring, and just kept going throughout the year.

Mosses love wet weather, but they shrivel into obscurity during dry times. With this year’s April monsoons, however, these little gems are now gorgeous and deep green.

“Mosses are incredibly beautiful,” said McKnight. “But until I started to work with them, I didn’t take the time to enjoy their beauty.”

I know that feeling. In part, I suppose, it comes from our natural tendency to pay attention to the big and obvious and gloss over the minuscule and obscure. It also comes from the intimidation factor: without the right tools, or help from a master bryologist, mosses are all but unknowable beyond a cursory, “That’s a Sphagnum, and that’s, well, not.”

“Common Mosses” is the perfect tool to get you started. The book is actually the result of a four-person collaboration. In addition to McKnight, coauthors include professional bryologist Joseph Rohrer, graphic designer and illustrator Kirsten McKnight Ward (she happens to be McKnight’s daughter), and photographer Warren Perdrizet (who was one of McKnight’s students). The crew has focused on 200 species that are common in the Northeast and the Appalachian Mountains, and all it takes to begin this voyage of discovery is the guide, a 10-power hand lens, a spray bottle to rehydrate dried mosses—McKnight calls this a “bryo-blaster”—and some natural curiosity.

Taking a cue from “Newcomb’s Wildflower Guide,” the much-beloved 1989 field book that emphasizes structural features of the flowers and leaves rather than blossom color, “Common Mosses” starts you on your journey by posing three basic questions. What is the plant’s growth form? What shape are its leaves? And does the leaf have a midrib or not? The guide then goes into considerable, user-friendly detail, complete with splendid drawings and photographs, to help you decide on answers.

First and foremost, there’s a query about Key Feature Number One: whether the plant in question is an acrocarp, a pleurocarp, or a peat moss—these relate to the moss’s growth form. A section about Key Feature Number Two offers instruction in determining whether the leaves are lance-shaped, ovate, hair-like, or akin to a tongue, a sickle, or a peat moss. (There’s also the possibility that the moss is leafless.) Finally, there’s Key Feature Number Three, which entails ascertaining the various leaf and midrib configurations, along with “tricky cases” that require some hand-holding for proper resolution.

“We’ve tried to provide the know-how that will guide a reader’s eyes to the characteristics that matter,” said McKnight. “If you know just those three things, you’ve made a huge step in the right direction.”

Once you’re in the proper neighborhood, you can try to work through what are known as dichotomous keys—investigation trails composed of couplets in which you have to choose between a series of pairs of characteristics. Say, for example, you believe you’re looking at an acrocarp—a moss with a simple or sparsely forked stem—with hair-like, lance-, ovate-, or tongue-shaped leaves with a midrib. That gets you to Key II, and if, after careful examination of other aspects, you arrive at Couplet 19 and decide that the spore-bearing capsule has a disk at its attachment-point to the stalk, congratulations! You’ve identified a moss called Polytrichum commune, the abundant Common Haircap Moss and one of the first species I learned using this terrific volume. If the situation is otherwise, you’ll just have to work your way through the next couplet, in which you’ll be asked to assess moss height, the kind of forest and geographical area the plant is found in, and characteristics of the leaves that sheath the spore-capsule stalks. Then, you’ll be able to decide if you’re looking at Polytrichastrum pallidisetum or P. ohioense, the Mountain or Oak Forest haircap mosses, respectively.

It sounds like a formidable task and, truth be told, it will require some careful work and study. But what, in natural history (or anything else, for that matter), doesn’t involve a bit of physical and mental perspiration? You can’t learn birds without spending hours in the field and hunched over your bird guides—well, actually, these days, you can, what with smart phone and tablet apps that do all the work for you, but that’s just plain wrong—and it has taken years, indeed decades, on my part to develop whatever modest amount of expertise I can claim as a naturalist. It ain’t easy, but the toil has been worthwhile and soul-satisfying, to say nothing of inspirational and, more often than not, fun.

So get this book and get out there to zero in on the mosses, which are at their eye-catching best right now. And unlike birds, insects, flowers, and many other things of interest, mosses are almost always available, in the same place, for study.

“I especially like their predictability,” said McKnight, who came of age as a student of fungi—his parents, Kent and Vera, wrote the “Peterson Field Guide to the Mushrooms” and he spent a lot of his childhood on mycological forays—so he knows volumes about unpredictability. “Ever since I started seeing the beauty and diversity of mosses, I just couldn’t help myself. I was hooked, and I wanted to look closer and learn more. Beauty and predictability, along with a great challenge—what more could you want?”

A note to readers: If you’re interested in mosses or any other aspect of creation, I’m leading a free public walk Saturday, April 26, from 10 a.m. until 12:30 p.m. at the Babcock Ridge Preserve in North Stonington, Conn. For more information, e-mail me:


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