The Last Word On Nothing

Yesterday: Urban Lichens, Part 1: OMG! Urban Lichens!, in which we learned that there are lichens in the city.

So I’d established that lichens can, sometimes, live in cities. The next step: round up a lichenologist.

On a sunny December afternoon, I met up with Manuela Dal Forno, a lichenologist. To be precise, she’s a lichen systematist. That means she studies how various species of lichens relate to each other. Originally from Brazil, she specializes in tropical lichens and recently got her Ph.D. from George Mason University in Virginia.

I had figured out for myself that there were two kinds of lichen on the young, new trees that had recently been transplanted near my office. One was a bold, sage-green, splotch with ruffled edges. The other was a subtler sort that seemed to lie closer to the bark. Two species of lichen, I thought. That’s interesting.

I had no idea.

We walked up to the first tree. “On this tree, you can probably get to five or six species,” Dal Forno said. She pointed. “This one is not a small one of this.” Two lichens that I’d assumed were the same kind, because both were that same sage green and both were ruffled, were in fact two entirely different species, one of which grows much skinnier ruffles. When she pointed it out, I could see the difference.

She opened her bag and pulled out the summer 2014 issue of Fungi magazine, a special issue on lichens, with a glamorous lichen photo on the cover. (For $60, you can get a one-year subscription, the lichen special issue, and a lichen t-shirt.) She opened to the article “Urban Lichens” and explained how lichens are classified.

There are three major kinds of lichens. The frilly ones are called foliose. The low-profile ones, without the edges that stand out from the surface they’re stuck to, are called crustose. A third type, called fruticose, are shaped like little trees or hairs, and generally can’t make it in urban environments.

Some identification can be done by eye in the field. The most striking lichen, the one with the big ruffles, was Flavoparmelia caperata, or Common greenshield. For others, you have to get more involved. Cross-sectioning and microscopes may be involved. So, too, may spot testing with chemicals that lichenologist call “C” and “K”—one has chlorine and the other has potassium. Lichens make many different chemical compounds, which can have colorful reactions when dabbed with these chemicals.

Dal Forno had also brought a field guide, Common Lichens of Northeastern North America. Unlike for birds, there aren’t a vast number of friendly, colorful field guides to lichens. This one was only published in 2014, by the New York Botanical Garden. It’s spiral-bound, with lay-person-friendly photographs and descriptions to help you and me identify lichens in the field.

“Let’s start,” Dal Forno said. Like any good lichenologist, she always has a hand lens on her—a snazzy one, with a built-in light. She started at about forehead level, leaning close to the tree, examining the patches of lichen. We counted the foliose species first. One had tiny black protrusions, called cilia. Another had no cilia and very tiny ruffles. A third had white dots, visible through the hand lens. A fourth was a little farther down. The fifth: our old friend Common greenshield, around waist height.

Next, she tackled the crustose lichens. They can be harder to identify, but just by eye we found five clearly different types—and examining them in the lab might have revealed them to be even more species. It wasn’t just that one light green kind I’d noticed. We found crustose lichens that were pink with black marks, light gray with little black reproductive structures, brown with black edges, and dark brown. More trees found us more species. The second tree we checked had a white one and a moss-green one we hadn’t seen on the first. On a third tree, we found still more.

The dark brown crustose lichen was particularly deceptive. I had assumed it was bark. In fact, on these young trees, the bark was barely visible. Almost every inch was covered with lichen.

We made one more stop, by a nearby major road, three lanes in each direction. I wanted Dal Forno to look at one of the older trees, which I’d only recently realized also had lichen on them. I stood in the narrow bit of sidewalk between the tree and the pavement while she examined the bark. A bouquet of four deflated balloons was tangled high in its branches.

On the side toward the road, it looked like someone had emptied the dregs of a bucket of chartreuse house paint. “Sometimes we see things, we aren’t sure if it’s a paint or a lichen,” she says–but a hand lens generally clears it right up. She counted four species of foliose lichen and one of crustose. All of them were hanging on to life as buses, cars, fire engines, and trucks rushed past, inches away.

Lichens are like sponges, soaking up pollutants, Dal Forno said. Some are fine in urban environments, but others suffer–like fruticose lichens, which seem to be particularly sensitive to sulfur dioxide. Lichens can even be used as indicators of air quality; if you know which species are living in a particular place, you can get a sense of how polluted the air is. I certainly haven’t seen any lichens as big as that first Common greenshield on the older trees right by the road.

I don’t know what will happen to the lichens on those young trees in the long term. There’s a more immediate threat in this heavily trafficked area, though. Back on those new trees, bits of the Common greenshields are already disappearing. I think those patches are just too tempting to the human hand; they’ve been partly torn off, revealing the bare bark underneath.

Photo: Helen Fields

Part 1 of 2: Omg! Urban lichens!
Part 3 of 2: Lichen beauty everywhere