IF YOU HAVE QUESTIONS about lichens, you call a lichenologist. And so I did—in behalf of worried readers asking what to do about lichens growing on the bark of trees in their garden. The answer: Celebrate! They are manna from heaven (and in fact that’s what manna from heaven was: two species of lichens).

That the presence of lichens is very good news comes on the authority of lichenologist Dr. James Lendemer, Assistant Curator in New York Botanical Garden’s Institute of Systematic Botany. Lichens, one of the earliest forms of land-dwelling life on earth, should be all around you in a healthy ecosystem: on bark, on mossy areas and other spots where the soil may be thin, on wood, and even defiantly on stones. They play key roles in keeping an environment in balance, too.

Read my conversation with James as you listen to the June 8, 2015 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).

Read more at the bottom of the page about the new lichen field guide, “Common Lichens of Northeastern North America,” published by the New York Botanical Garden Press.

read/listen: my lichen q&a

with dr. james lendemer

Q. Unfortunately the most common lichen question I get asked as a garden writer is, “How do I kill the lichen on my trees?” And of course the answer is, “Don’t!”

A. Whatever you do, don’t. [Laughter.]

Q. So before we get to more on that, James, what are lichens? Maybe it’s easier to say what they’re not—like, they are not plants, are they?

A. They aren’t plants, and they’re also not animals. Historically, lichens were actually considered to be plants; they were originally classified with them. That’s why you’re calling a botanical garden to talk to a lichenologist—whereas most people that study fungi are at institutions that study plant pathology or things like that.

These organisms were traditionally treated with plants, but in fact they’re actually fungi that have evolved a unique lifestyle that involves capturing an alga for the purposes of obtaining nutrition.

Q. So “capturing an alga”—like algae?

A.Yes; some people call them “fungi that have discovered farming.”

Q. “Fungi that have discovered farming.” So that’s what they are—they’re very clever creatures, aren’t they?

A. That lifestyle has really helped them to adapt and survive in some of earth’s harshest habitats—to really be able to take over and become diverse and abundant pretty much everywhere on land, all over the world.

So lichens are actually fungi, and they’re fungi that get together with this alga and form a body that looks completely unlike the two different parts, the two different organisms. What you see in the wild is this composite organism formed by the two. It’s dominated by the fungus, but the algae are in there, too.

Q. They have their own whole language. Is what you just described a cryptogam?

A. Think of cryptogams as sort of the lesser plants—so it includes the ferns, for instance. Traditionally in botany, cryptogams include all of the forgotten or lesser-studied or smaller organisms; things that don’t have flowers for the most part. So you’re thinking of ferns, of the bryophytes (mosses and liverworts) and then lichens and fungi and algae as well.

Q. How old are lichens; when did they first come on the planet?

A. It’s very interesting: Lichens are thought to be one of the earliest forms of land-dwelling life, which is easy to imagine if you have a fungus floating around in very ancient oceans, and then you also have algae out there. Getting together and forming this composite organism is a way for the fungus to get onto land, and also a way for the alga to get onto land.

The alga gets protection from the fungus—it’s living inside the fungus—and the fungus is getting nutrition from the alga, in what’s potentially an area where there wouldn’t have been a nutrition source to start out with.

Q. So it’s a successful partnership.

A. Oh, for sure.

Q. Do they occur worldwide, and in a diversity of habitats? What can we say about where they are and what they need?

A. Lichens should be all around you—on trees, on rocks. As you so eloquently put at the beginning of the show, they should be on trees, on rocks, on old logs, on soil—really anything that they can grow on they will grow on.

Q. Any substrate?

A. Yes, and in Antarctica—in the harshest conditions where there is a rock exposed in Antarctica, there will be a lichen. In the harshest deserts of the arid West, and in Africa, there are lichens there. They survive and thrive in many places where plants and animals cannot.

Q. There are many colors of lichens—why? We said they are composite organisms, but why are some more orangey and some gray, some greenish, yellow…how does that happen?

A. What causes that remarkable variation in color that you see in nature? The color that you see is actually substances that are secreted—chemicals that are secreted by the fungus. They sort of aggregate around the fungal hyphae, around the individual fungal strands that form a fungus. They actually are secreted and then sort of crystallize around them.

Those pigments you’re seeing are often in the upper surface or the outer layers of the lichens. Those are actually functioning in many ways, and one of the primary ones is thought to be as a protectant from UV radiation—it’s protecting the fungus and alga inside the actual lichen.

Q. Amazing.

A. They’re not just doing it for us, for our pleasure, but we can appreciate them nonetheless. All those different colors—the reds, the oranges, the yellows, the greens—those are all different substances produced by different species of lichen.

It should be said that lichens are remarkable because they produce hundreds or thousands of chemical compounds not found anywhere else in nature, and some of them are known to have biomedical or bioactive properties.

Q. Have they been used in medicine, and in other ways ethno-botanically?

A. Yes, for thousands of years. I like to say that lichens, and more generally speaking fungi, are cultural touchstones for humans to sort of understand the truly diverse cryptogam diversity that exists in nature.

There’s this tremendous diversity—millions of species—that most people don’t appreciate, actually occur all around them. Lichens and fungi in general are the one touchstone people have, because they have these deep, long-running cultural connections.

Many native peoples’ belief systems actually involve fungi and lichens. The Biblical manna from heaven—that was a lichen.

Q. I didn’t know that.

A. We even know what species they were—two species of crustose lichens that grow in the deserts of the Middle East. In the mornings, when everything sort of dews up a little bit, they puff up and so they appear to come out of nowhere.  That’s what was eaten in the desert at that time. Isn’t that remarkable?

Q. You just used the word crustose. We talked about the diversity of color in lichens, but there are also textural groupings, and crustose is one, yes?

A. Yes. If you have your Biology 101, what most people learn about lichens is that they come in more or less three different growth forms. And those forms refer to the thallus, or body, that the lichen is forming—that composite organism of the fungus and alga.

The first form is fruticose—bushy and branching and very three-dimensional. They stick out from the substrate, like little trees. If you have a model train set and have the fake trees they use in model train sets, those are often made of fruticose lichens that have been dyed.

Q. Manna from heaven, toy train trees…

A. Where aren’t they? [Laughter.]

The second type are the foliose lichens, and those are the lichens that are leaf-life, with an upper surface and a lower surface. They aren’t actually attached to the substrate that they grow on, but rather they’re attached by secondary structure that are similar to roots, but they don’t actually uptake nutrients. They’re just attachment organs.

The most diverse kind (and the least studied) are the crustose lichens, which are basically just a paint, more of less. Some people think of them as stains, but I prefer not to think of them that way.

Q. That’s a negative word.

A. We like to trend positive. But you can think of them as paintings on trees, rocks, what have you. They have an upper surface, but they have no distinct lower surface that separates them from the substrate. They don’t have those attachment organs; they’re just growing directly on the substrate.

Q. The way I learned about lichens–as many things happen for me, I was out in the garden, and had my camera, and there was this unusual-to-me-insect on the side of the barn. I took a photo [above], and then also took a photo of some lichens on stone across the yard [below]. When I went inside to key out the insect, I found out it was a painted lichen moth. That’s not an insect that has an interest in the lichens on the stone on my patio…but this led me to the “aha” that lichens do more than sit there and look intricate and beautiful. [Laughter.]

There’s this whole interaction: someone might eat them or live in them. Flying squirrels use them for their nests?

A. And hummingbirds.

Q. They collect lichen as well? Interesting. So what other examples are there of what they’re doing here, and how they fit in?

A. I like to think of it—and it may be my bias as a lichenologist [Laughter]—if you have a forest, or an ecosystem you can think of lichens as being hubs within that ecosystem.

There are many different processes that are going on—it’s a very dynamic system. If you’ve been in a forest or been in a garden, you know that nature is very dynamic naturally. A lot of that dynamism happens around, and through, lichens. So lichens are involved in all sorts of things. If you think of what they’re eating, and what’s eating them: They’re very important in breaking down rocks, so they form soil.  If you have lichens, you’re able to form soil, and you can have mosses and plants grow. If you didn’t have lichens doing that, there would be a lot slower erosion of rocks, and a lot slower formation of soil.

They’re also important in nutrient cycling—like in Nitrogen-fixing.

And if you’re thinking of it as what is eating them, it ranges from animals as large as caribou, which rely almost entirely on lichens for their winter diet—without lichens they wouldn’t survive. And animals as small as flying squirrels or hummingbirds making nests, and then it gets even smaller.

There are hundreds if not thousands of unique interactions between insects and other invertebrates and small animals—like your lichen moth [above, yellow and black lichen moth at Margaret’s garden]—that either eat the lichen, or use the lichen as camouflage to protect themselves.

If you go at an even smaller, finer scale: Within the lichen itself, within that body composed of the fungus and the alga, there is a whole tiny world or universe that includes many forms of life that occur nowhere else outside of it.

There are micro-invertebrates, like Tardigrades or water bears—if you’re not familiar with what a water bear is, I strongly urge you to Google that. There are beautiful color scanning electron micrographs on the internet of them. Fabulous little creatures—and they live in the intercellular space of the lichens. And there are unique fungi and bacteria that live within the lichen themselves, that don’t occur outside of them. A lichen is a very complex, dynamic thing.

Q. I was sitting in a restaurant recently in the Berkshires of Massachusetts, a place I go regularly, looking out to a woodland edge alongside a wetland. I noticed something I hadn’t before: Every tree among many, many very old trees there were covered with lichen. So beautiful. But then I drove home not far away, and on my road, there is not so much of that. 

I know it’s a question you can’t answer without being there, but generally speaking, why would one place be so extraordinary in terms of lichens?

A. It shouldn’t be. If you look at lichens historically—and we know this thanks to the resources at museums and institutions like the New York Botanical Garden, where we’ve had scientists collecting lichens, plants, all sort of things for centuries—we know based on historical specimens that many species of lichens were more common and widespread than they are today.

Really it’s the same story that you hear with many other components of biodiversity—the loss of wildflowers from many regions, the decline of wildflowers, the decline of migratory birds. The extinction crisis that we’re in right now; the biodiversity crisis that is looming.

That is something that lichens have been experiencing for some time, but they’re one of the most visual symbols or ways that people can connect with what’s happening in the environment, because lichens are kind of like a canary in a coal mine.

Q. I was thinking that: They’re like a bellwether, or a canary in a coal mine.

A. They’re excellent indicators of air pollution especially, or habitat quality in general. When an ecosystem or the environment in general is degraded in any number of different ways, the lichens are often one of the first and most visibly impacted groups of organisms.

So that’s what you’re seeing: Either there are legacy effects, or ongoing effects, from the change that we are wreaking on the natural world. If you go to mature old-growth forests that exist in major cities—for instance, Fairmount Park in Philadelphia or the Thain Family Forest here at the New York Botanical Garden—we have old forests with mature trees, but they’re virtually devoid of trees. The reason for that is the air pollution and the overall habitat degradation that persisted for over a century.

The Clean Air Act significantly improved air quality, and as a result lichens have begun to recolonize in many areas where they were extirpated in the past. But that being said, it’s a very slow process that takes centuries if not longer.

What we’re seeing is really the legacy of the Industrial Age, you could call it. We actually here at the Botanical Garden have begun to reintroduce species we know grew here 150 years ago. We attempted to reintroduce them here with the thought that our air and our water has gotten a lot cleaner. We are interested to see whether or not with a little bit of a helping hand we can bring species that occur maybe 100 miles away, and would have occurred here historically, to grow here again.

The problem is not so much the quality of the environment now in some places so much as how species have been pushed away from such vast areas, that they can no longer recolonize. A lichen can only move so quickly.

Q. I want to mention as I did at the beginning: So many people see lichens on a tree and think it’s a parasite, or a disease. But it’s not an indicator of some problem.

A. It’s an indicator of good. [Laughter.]

Q. I wanted to have you say that, because you’re the lichenologist.

A. Lichens do not harm the substrates that they’re growing on. They don’t have roots that penetrate into the substrates; they’re not obtaining nutrients from trees or shrubs they’re growing on. They get all their nutrients from the algae, and from the air particulate matter and the water vapor in the air—which is why they’re so sensitive to air pollution and other forms of environmental degradation.

So don’t cut them off your trees.

Q. Celebrate them.

A. Yes.

Q. And in anticipation of our conversation, I went out again this morning with my camera, and I thought: I’m just going to walk around my place, which is 2 acres, and I’m going to take a picture of every lichen I can find. It was so interesting—there were so many I had never noticed.

Do you recommend doing that with a hand lens? This new field guide from New York Botanical Garden Press is great. [James using a hand lens, above, and a detailed photo from the new book.]

A. It’s a unique resource; there is nothing like it that has been published before.

Q. For real people.

A. Yes, not just for scientists, for real people. It has beautiful color photographs. You could open that book to a page, and if you had a hand lens and you were looking at a lichen, you could with a high degree of probability identify the lichen, if you were in the Northeast. Historically many of the field guides has fuzzy pictures, in black and white, and didn’t do the lichens justice. It made it hard for people to identify them. This book makes them much more accessible. It’s a way for you to appreciate a component of the flora and fauna of your backyard that a lot of people might not have been aware of or appreciated before.

Q. And they’re important organisms—not just beautiful. They’re trying to tell us something about what’s going on around us.

A. They’re like the canary in a coal mine, and they’ve been singing for over a century. Unfortunately nobody has heeded their song.

prefer the podcast version of the show?

MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its seventh year in March 2016. In 2016, the show won three silver medals for excellence from the Garden Writers Association. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the June 8, 2015 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).

enter to win the lichen field guide

I’VE BOUGHT an extra copies of “Common Lichens of Northeastern North America,” published by the New York Botanical Garden Press, to share with a lucky reader. All you have to do is answer this question in the comments box at the very bottom of the page (after the last reader comment):

After reading this story or listening to the podcast, what surprised you most about lichens? What didn’t you know?

Silly me: I had no idea about their role in soil-building, by helping rocks break down more quickly than would otherwise happen. (I didn’t know about the manna from heaven-lichen connection, either.) I’ve long loved them, and knew they were good news, but not in the detail James Lendemer shared.

Feeling shy, or have no answer? Just say, “Count me in” or something to that effect, and I will, but an answer is better. I’ll pick a winner U.S. or Canada) after entries close at midnight Sunday, June 14. Good luck to all

(All photos except lichen moth and lichen on Margaret’s patio from James Lendemer, used with permission. Disclosure: Purchases from Amazon links may yield a small commission.)