the wonder of lichens, with jessica allen

SOME OF THE most beautiful and intricate creatures in the garden are not plants at all. A diversity of lichen is showing off right now on tree bark and branches, on stones, on unpainted garden furniture and even soil, more visible since many of the garden’s plants have quieted down visually for their dormant season. Let’s go on a virtual lichen walk with lichenologist Jessica Allen, co-author of a new book on the subject.

Jessica Allen is an Assistant Professor of Integrative Plant Biology at Eastern Washington University. And before that she pursued her PhD at New York Botanical Garden in a joint program with the City University of New York. At NYBG she met lichenologist James Lendemer, and years later, when she conceived of creating the new book, “Urban Lichens: A Field Guide for Northeastern North America” (affiliate link), she invited him to collaborate, as they have continued to do on lichen research work over the years. (Photo below, by Paul Super, is of the pair examining lichens in the Smokies.)

Plus: Enter to win their new lichen field guide from Yale University Press by commenting in the box near the bottom of the page.

Read along as you listen to the November 29, 2021 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on Apple Podcasts (iTunes) or Spotify or Stitcher (and browse my archive of podcasts here).

the world of lichens, with jessica allen



Margaret Roach: Welcome, Jessi. Oh, we had so much fun doing the recent “New York Times” column on lichens, which people seemed to really enjoy, so I couldn’t wait to talk to you again and ask you more questions [laughter].

Jessica Allen: Absolutely. I thought the article turned out really well, and I was absolutely delighted with the comments, too. A lot of people shared their memories of lichens, how they visualize lichens and interact with them, and it was just a delight to be able to read those comments.

Margaret: So I suspect every conversation you have about lichens—every class you teach, or walk you lead, or lecture you give, or paper you write—you always have to begin with the answer to this question: What’s a lichen? [Laughter.]

Jessi: Yes, absolutely. They’re so mysterious, right? They are these organisms that we see around us, but their underlying nature isn’t necessarily obvious just from looking at them macroscopically. And if we were to take a microscopic look there, what we find is that they’re fungi and algae growing together. So they’re sort of a quintessential symbiosis. Some people think of them as corals that live on the land.

Margaret: Oh!

Jessi: So there’s this really obligate, intimate interaction between the fungus and then some sort of photosynthesizing partner. So whether that’s a green alga or a cyanobacterium, or a combination of green algae and cyanobacterium with the fungus. And that is really the cornerstone of the symbiosis.

But there’s a lot more going on in there than just those two organisms. We can really think of lichens as miniature ecosystems in and of themselves as well. So in addition to those—the fungi, the algae—there are other fungi in there, there are tons of bacteria. There are tardigrades, which are water bears, and nematodes, these tiny worms, and so really it’s a microcosm in and of itself.

Margaret: So you studied to become a botanist, a plant biologist. Why at one point did you not say oh, this genus of plants, or these trees? How did lichen capture your heart?

Jessi: Yeah, that’s a great question. It actually started when I was taking introductory biology. And for the whole year, we went through all of these chapters in this book, and we talked about all of these different organisms and molecular processes. And then the only chapter that we skipped was the one on fungi.

So I went back and read it and I said, “These are the coolest organisms.” And I was lucky enough to be at a university where we actually had a whole quarter-long class on mycology, and the professor was wonderful. And I really fell in love with fungi. I think they’re fascinating. They are a bit cryptic, so there’s a lot of mystery there. There’s a lot that we don’t understand about them still.

And then of all the fungi I found lichens the most beautiful, and I really just fell in love. And so throughout my education and also my research, I’ve worked on plants, I’ve studied plants, but really my heart has always been with the lichens.

Margaret: Interesting. I didn’t know that that’s how it came about. And I think that when I spoke to you and James Lendermer, your longtime colleague, for the “New York Times” article, you both explained to me that fungi are really overlooked in conservation as well, aren’t they? Right there you’re just telling a story about how you discovered them, and they were almost overlooked in the literature, so to speak. But they’re not really recognized in conservation efforts as widely as they should be, are they?

Jessi: Absolutely. For a long time they’ve really just been completely excluded from our typical conservation efforts, which tend to focus on the larger animals and on plants—on vascular plants especially. And we can see this when we look at, for instance, the Endangered Species Act. There are thousands of plants and animals protected by the ESA. But there are only two fungi. They’re both lichens, and they both occur in the Southeastern United States. So that’s the rock gnome lichen and the perforate Cladonia lichen in Florida.

And there has been some recent, actually some really recent, positive news on this front, though. Lichens and other fungi are gaining a lot of global attention in conservation. The first international fungal conservation organization just formed. The Fungal Conservation Committee is part of the International Union for the Conservation of Nature. The IUCN has really been embracing fungi in their documents recently. We have this flora, fungi, fauna movement going on—this three Fs movement, which has really been led by Giuliana Furci, who’s an incredible fungal conservationist. And so there is a movement in this direction. I think we’re really seeing some positive outcomes for fungal conservation globally really.

Margaret: So in the case of lichens, people might say, “Well, but it just looks like a piece of chewing gum that fell on the ground, or a log, or some splat of paint on a rock or whatever, so why should I care about those?” Why do we need… So what’s their role in the bigger picture environmentally and so forth? What are they doing?

Jessi: Yeah. So lichens perform tons of different ecosystem services. They interact with a lot of animals. So many animals eat lichens, even large mammals, so like caribou eat a lot of lichens. They really fundamentally rely on lichens as one of their major food sources. But even animals like deer and moose use lichens, especially as a winter forage.

Many birds use them as nesting materials, as do smaller mammals, like flying squirrels, both as nesting materials and as food. And then if we continue to scale down, many invertebrates use them as camouflage and again, as a food source.

And then if we scale up to the ecosystem-level processes, they’re fixing carbon from the air, and they’re also fixing nitrogen. And they can be, in many systems, really one of the most important nitrogen inputs to the soil in some forested systems.

Margaret: Oh.

Jessi: So they’re both on this really large scale of the movement of elements through these systems globally, and on these smaller scales in all of these interactions with animals.

Margaret: Huh. And I know when we did the story together we talked about here it was garden cleanup time when we were speaking and people are raking and they’re finding maybe a branch, a twig, with lichen on it. But it’s not junk. It’s, as you called it, “a little packet of fertilizer,” of potential fertilizer. I mean, as it decomposes it’s also full of goodies for the ecosystem in that way.

Jessi: Yes, absolutely. And so you can think of that in the context of composting, if you’re thinking of gardening. And then I would encourage folks if you’re ever out in the forest walking around and you see that same process happening with these fallen branches and lichens on there, and you will see them decomposing and becoming part of the soil. And that nitrogen input is an especially important part of what lichens bring to that picture.

Margaret: Yeah. How long do they live?

Jessi: [Laughter.]

Margaret: It doesn’t seem like it’s really like youth, adolescence, adulthood and senescence. It doesn’t seem like that [laughter], like other organisms that I know better.

Jessi: Yeah. Yes, absolutely. If those really distinct life stages are not necessarily observable with lichens, they prefer to play by their own rules in many, many ways, and their lifespans vary quite a bit. So we have an example of, for instance, if we look at lichens that live on leaves, so what we call foliicolous lichens in the tropics, those lichens entire lifespans are tied to the length of time that that leaf is attached to the plant.

Margaret: Oh.

Jessi: So we see a lifespan of a year, two years maybe. And even in the United States we have lichens that live on, for instance, rhododendron leaves, and those leaves last for about two years, so that’s the whole lifespan for the lichen.

Margaret: Oh.

Jessi: And then on the other frastic farther end of the extreme lifespans we see, for instance, really small lichens that live in the Arctic that grow slowly. They have really short growing seasons. These lichens, I don’t know that we necessarily even have a number on how long they could live, certainly well over a hundred years. So we have this broad range, but I would say for the most part, the lichens, if you’re in a temperate forest that you see growing on bark and they’re kind of leafy, we’re talking maybe 10 to 50 years-ish. So, they tend to be fairly long-lived organisms most of the time.

Margaret: Yeah. I mentioned in the introduction that I feel like especially in the fall—I’m in a snowy area so before the snow falls and covers some of them—but especially in fall, and then again in early spring, when I’m not distracted visually by the “garden” or leaves on the trees or whatever, I’m really tuned into the lichens most of all. And do they ever go dormant? Do they have a dormant time, or are they doing their thing, the alga in the fungus, is it photosynthesizing all the time, all year-round? Or how does that work?

Jessi: Yeah, that’s a great question. So their growing season, I would say, is much longer than many vascular plants, and they have this… Well, I would say one of their super-powers is that they can completely desiccate and go dormant, and then rehydrate and within an hour they’re like back at it, doing their thing. And then they can desiccate again.

Margaret: Oh.

Jessi: So their water content is at equilibrium with the environment, and they can be photosynthetically active at much lower temperatures than you would suspect. So not all lichens, but many lichens can really have a low rate of photosynthesis, getting even close to freezing temperatures. So if you think about in the fall, for instance—and actually the fall and the spring are great times for lichens to grow because all of the leaves are out of the way, so they get a larger share of the sun coming in onto them. And so when they’re hydrated, and the sun is up, and it’s above freezing, they’re probably photosynthesizing.

And then they can also be active at night. They’re not necessarily photosynthesizing, but there are some physiological activities that can be going on as long as it’s warm enough and wet enough for them to be doing their thing. So I really think about lichens growing and being active more on a… I guess I sort of envision these conditions and when they might be present over the course of any given 24-hour period. Warm enough, enough light and enough water for them to be active.

Margaret: Right. O.K. So there are maybe, I think, something like 25,000 species known, and hundreds more discovered each year, something like that. And I think in the book, “Urban Lichens: A Field Guide for Northeastern North America,” which would be appropriate for anyone in the Northeast, not just in a city but throughout, I think, and down to maybe Washington or something… You cover, I don’t know, maybe 60 or so in very detailed portraits.

So if I’m going to go out and I’m going to look around my garden, and I’m going to discover lots of different ones, to narrow down what they might be… I might have your guide because I’m in the right region or a different guide if I’m elsewhere, it helps to first decide which type of lichen, which group they’re in. And there’s three main groups, right, and that’s the first way of narrowing down the choices. Is that how we start?

Jessi: Yes, absolutely. So if you go out into your garden looking for lichens, I would say my first tip is that they’re best enjoyed with a little bit of magnification. So if you have a magnifying glass or a jeweler’s loop or a hand lens, definitely take that with you. And then certainly figuring out which growth form the lichen that you’re looking at is, is a great place to start. [Above, top to bottom, foliose, crustose and fruticose lichens; photo by Jordan Hoffman.]

So we have three main growth forms, foliose lichens, which are sort of leaf-like. They have a top surface and a bottom surface. If you try to maybe pick at them a little bit and see if they come off of whatever they’re growing on, you should be able to get them away from their substrate a bit.

So then you might also find crustose lichens, which are completely and intimately attached to whatever they’re growing on. Some of them are a little bit scuzzier looking [laughter], not to have too much of a-

Margaret: Those are the ones that could be mistaken for paint splatter, I think sometimes, huh?

Jessi: Absolutely.

Margaret: Yeah.

Jessi: Definitely. So they tend to be very strongly attached to whatever they’re growing on. And then the third growth farm are fruticose lichens, so they’re more shrubby, they’re really 3D. They’ll be growing up off of whatever they’re on, whether that’s bark or if it’s the ground. And we have things like old man’s beard in that group, or reindeer lichens, or British soldiers lichens—species like this.

Margaret: It’s so fun if you take the little lens, even an inexpensive hand lens, and you get right… Say it’s on rock, I did this in taking some pictures for our article. And you get right down at the rock surface level, and you look at this community of different lichen on one surface. And you see those fruticose ones, those shrubby ones, standing up, it’s like a miniature world. And then the crustose ones really adhering to the rock, and in between some foliose ones.

And it’s like oh my goodness, I had no idea. Because if you’re just zooming around doing your garden chores, oh, there’s some lichen over there—but you don’t really look. And so your point is very well taken. Take that lens and look at it from all angles, and just see how intricate and how incredible they are.

Jessi: Yeah, absolutely. I think this is one of the things that I find really captures people’s imaginations the most. We sort of take it for granted that they’re there, they’re a splash of color. But then, when you look, even with—again, you don’t need anything fancy, just a little magnification—and it’s this whole world, this whole beautiful world. It’s around us all the time and we tend to rush past it, but it is an invitation to slow down and take a closer look.

Margaret: Yeah. And as far as what they’re doing, they’re not rooting into or feeding off the tree that they’re on, if they’re on tree bark or on a branch or whatever. They’re not parasites, I guess, is the word I want to say. They’re not, I guess maybe that’s one of the words I want to say, but they’re not in some way harming the other living thing or the rock for that matter. They may speed the breaking down of the rock into a component of soil, but they’re not doing that rapidly. They’re not doing damage, right?

Jessi: Yeah, absolutely. So the lichens that grow on bark are just using that as a place to live, to access the sun. And bark tends to have a little bit of moisture-holding ability, so it’s just a really nice place for them to live. The same on rocks, on soil. They are involved in this process of rock weathering and eventually soil formation, but like you said, this process takes a long time. So in our lifespan, and in our gardens, we wouldn’t necessarily see any of our rocks really breaking down quickly because of lichens.

Margaret: Right. And not only do we not have to, but we must not scrape them off the tree. You know what I mean? They’re not a disease. They’re not an infestation. They’re not something bad on the bark of the tree. It’s fine. It’s great. I mean, I think it’s to celebrate, not to worry about [laughter].

Jessi: Absolutely. I agree. And if you’re seeing lichens on your trees, yes, they’re not harming the trees at all. And indeed, lichens are really very sensitive to air pollution. They’re sensitive indicators of air quality, of environmental quality, and so if you have a ton of lichens on your tree, that’s probably a good sign. And so I agree, absolutely. Celebrate that.

Margaret: Yeah. I want to talk about the book a little more and how that came about. You were leading walks, I think in the city maybe, and doing what are called bioblitzes, participating in bioblitzes, where all the species in a given area of different kinds are surveyed, assessed. And that led, I think, to your thinking, “Gosh, we need a guidebook that shows the lichens of this region.” Is that a fair assessment?

Jessi: Yeah, exactly. It really came out of engaging with people in New York City, specifically with various groups of students and naturalists, and being explicitly asked every single time, what’s next? Like, “This was fantastic. I loved learning more about lichens and taking a closer look, and I want to keep going with this. What resource do you recommend?”

And there are some great field guides out there, but nothing for urban areas, and lichens in urban areas tend to look slightly different. The cityscape is a bit of a stressful environment, and so it changes their morphology in really specific ways, and so it’s challenging to use field guides that are designed for lichens occurring in natural areas in a city. And so I started writing this explicitly because of that request. And I think it turned out pretty well.

So, we have an introduction to lichens, all of the background that you need to know to get going and identifying lichens, appreciating lichens. There are detailed descriptions and notes on 60 species, with photographs. There’s a key. And then there’s also an illustrated glossary at the end. So with this in hand, you should be able to go out and start lichenizing.

Margaret: And really again, not just in New York City, but throughout the East, because I mean, I’m here a couple of hours or few hours north of the city and so still in the East, but not in an urban setting. And it’s working for me. I’m seeing familiar ones in here.

And does the city have more like a hundred species, or how many species do you think there are in New York City, for instance?

Jessi: So when I last tabulated that number a few years ago, we were up to 106 species having been reported from New York City since the late 1960s.

Margaret: Wow.

Jessi: And since then, a few additional species have been reported. I think we’re looking at about 120 species within the five boroughs, at this point.

Margaret: Huh. Wow. And you told me before that once you had to go do a walk or a something at the big landfill, the big capped landfill at Staten Island, Fresh Kills. And you were like, “There’s not going to be anything here.” And what did you find? I mean, so it’s even in preposterous places, they are there.

Jessi: Yeah, absolutely. That was actually a really fun event. That was one of the Macaulay Honors College bioblitzes. So I was out there with my colleague, Natalie Howe, and a number of undergraduate honors students. And yes, exactly. I said, “Oh my gosh, what are we going to find here?” And then we actually found quite a few species, including one that was growing on a discarded brick. There were a number of species that we actually hadn’t seen in any other parts of the city. So there are surprises to be found everywhere. I think that we are still just getting a sense of what is possible. Like, what lichens can possibly live, even in these really dense urban areas?

Margaret: Yeah. Well, Dr. Jessica Allen, thank you so much. And thank you for “Urban Lichens: A Field Guide for Northeastern North America,” and just for being patiently telling us more about these incredible creatures. So everybody should go out and do a lichen walk and take that hand lens, as she was explaining. And I hope I’ll talk to you again soon.

enter to win a copy of the lichen field guide

I’LL BUY A COPY of “Urban Lichens: A Field Guide for Northeastern North America” (affiliate link), by Jessica Allen and James Lendemer, for one lucky reader. All you have to do to enter is answer this question in the comments box closer to the bottom of the page:

What surfaces in your garden are home to lichens, and do you enjoy seeing them?

No answer, or feeling shy? Just say something like “Count me in” and I will, but a reply is even better. I’ll pick a random winner after entries close at midnight Tuesday, December 7, 2021. Good luck to all

(Disclosure: As an Amazon Associate I earn from qualifying purchases.)

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 11th year in March 2020. 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 November 29, 2021 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes/Apple Podcasts or Spotify or Stitcher (and browse my archive of podcasts here).

  1. Janice Brewer Smith says:

    I have been seeing flat splotty lichen on trees and scrubs. Took down a whole rose of Sharon tree cause I thought the sploshes of lichen meant it was diseased! This has been a great lecture today!

  2. Achala Wali says:

    Lichens are visible on many plants in my garden — from the pine trees to older lilacs. I’m also actively collecting lichen covered branches on my walks to distribute around the garden. Very informative blog!

  3. Adrienne Roth says:

    I recently have renewed interest in lichen from a study on paint pigments. I also read that lichens existence are a good indicator that the environment that they live in is relatively free of polution.

  4. Andrea says:

    I never realized how interesting lichens are! We mostly see them on our wooden fence, often on rocks and a few tree trunks and sometimes on the house roof. This interview is very informative!

  5. Deitra says:

    Count me in! I’d like to learn more. I enjoy seeing lichens on a kousa dogwood outside a window, Japanese maple, rock steps near a pond, and on the wood roof of a bird house.

  6. Tia P. says:

    I have numerous trees and shrubs that have bark lichens. I have some stone work that has been in place for 12 years and has some lichens starting on the rocks.

  7. Alan says:

    There are lichens on some largish stones, on the bricks in the yard, and across the sidewalk, particularly in the shade. I’d love to know which ones they are.

  8. L.J. says:

    My “garden” is (are?) NYC’s parks — and just about any outdoor surface where I spot lichen-contenders and bother to peer in. Yes, I do enjoy the peering, though I’m hopeless with a hand lens!
    First encounter: a late 2015 blizzard stroll, Riverside Drive — snow massed knee-high, tree trunks like coal against the white. Peered in a bit: crustose lichens, I learn from this show (thanks Jessica!).
    More lovely looking, nothing systematic, ever since: crustose painting the backs of wooden slats of park benches, tree trunks (of course). And, perhaps my favorite sighting: Reindeer lichen on street trees and downed twigs while walking to the train from the Parrish Art Museum (way out on Long Island. Which made a deeper impression — the lichens, or the art?)
    Almost took some home, but left them”in situ”, their habitat, instead.
    Thanks much, Jessica — and thanks, Margaret, for this and all your shows. They’ve kept me sane through the pandemic.

  9. Karen Meyer says:

    Rocks and trees, for sure. But I’ll be looking harder for these.
    I visited a beautiful bay on Lake Superior which had orange
    lichens growing profusely on the shore rocks and trees.

  10. Jeanne F Doherty says:

    Hi ,
    I know I have seen lichen but I didn’t realize what it was. I have seen some on concrete and sticks and just assumed it was mold, but I guess it could have been lichens. I would like to learn more about lichens so I will know the differences between them and other growing things. Now that I know a little more I will be on the look-out for them!

  11. Shari Sisco says:

    I first learned about them in Big Bend National Park, I just bought a home in Northern Baja and we have lichens growing on the trees in our yard!!

  12. Linda Fizgerald says:

    I love lichens also. They are growing and all over my old grayed cedar furniture on my patio.
    Such intricate and natural beauty. Found also on many large rocks and trees on my property
    here in CT.

  13. Robin Faye says:

    What a beautiful and interesting topic to explore over the holidays!! I have an artist friend who paints lichen in greatly magnified form and I have sent her this link. Such a beautiful endeavour. I look forward to exploring your links and comments. Thank you so much for sharing!

  14. Carol Mendonca says:

    this is amazing information that I want to learn more about. I live in Taunton, Ma on 3/4 acres with different trees. One is a birch tree right off the deck. It has lichens on it that I will read about. my landscaper told me that the air quality around my home is good because he looked at the lichens. I always thought that the Vermont Monks used it in their baking as a substitute for yeast! I need to continue to investigate. I would really love to win a copy of this book to share with folks.

  15. Charlotte says:

    Lichens: In our Chicago lakefront garden (I manage the gardens at the Shedd Aquarium) they especially love the bark of our aging crabapples which are positively encrusted with them and are a real sight to behold this time of year.

    Thanks for reminding us of lichens. I’ve had a relationship with them since I was a kid growing up in Berkshire County MA. “British Soldiers” as we called them were a favorite and ended up in many a terrarium.

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