Friday, July 26, 2019

Lichen or Not: The Fascinating World of a Symbiotic Organism

by Anna Caputo
AmeriCorps Member

A diversity of lichen in Brownsville, VT

Carl Linnaeus. The Linnaeus. The guy who documented and classified a sizable chunk of Earth’s known species, the father of taxonomy, the guy you learned about in high school biology and immediately forgot, insulted one of my favorite taxonomic groups. I don’t know what the eighteenth century botanist had against Lichens, but he described them as “the poor trash of vegetation,” classified them into one genus, and paid them little attention thereafter. I speculate that his opinion of them was skewed because Lichens aren’t plants. They aren’t technically fungi either. In fact, they’re a bit of an anomaly when it comes to categorization, yet these perfectly balanced symbiotic communities are some of the strangest macro-organisms in forests, or on rocks, fence posts, roofs, and sidewalks.

Common Greenshield (a foliose lichen)
To explain why they are so unique, one has to appreciate symbiosis. Symbiosis is defined as an interaction between different organisms living in close physical association, typically to the advantage of both. There is symbiosis between clownfish and the stinging anemones they reside in, between rhinoceroses and oxpeckers who perch on their backs, and even between humans and the microbes that live in us. Symbiosis is a partnership. The symbiotic relationship in Lichens is a profound one, so much so that the word 'symbiosis' was originally coined in 1877, by biologist Albert Bernhard Frank, just to describe them.

A single Lichen is a community: multiple organisms working together to survive. They are two to three codependent entities at any given moment. This relationship starts with the scaffolding: the part that gives Lichens their strange shape and structure, which is provided by fungi in the family Ascomycota, also know as the cup mushrooms. The thing that sets Lichens apart from the rest of the cup mushrooms is that they have essentially dropped their mycelium (the root system of a mushroom) and picked up agriculture in its stead.

Bristly Beard Lichen
The “crop” that they grow is algae. Algae live inside the Lichens, and provide the symbiotic community with food: glucose and carbohydrates. For a group of Lichens known as Parmelia macrolichen, there is a third partner. They have a yeast (the same stuff used to make bread and beer) that was discovered in the mix for the first time in 2016. Lichenologists speculate that the yeast acts like the Lichen's security guard, producing chemicals that help protect it from predators or microbes.

That’s all in one lichen! None can exist without the other, but what can a fungi, an algae, and a yeast do together that other plants or mushrooms cannot do on their own? Lichen is the life-form that can grow where no plant has grown before. They are among the first organisms to colonize inorganic material like bare rocks. Take a lifeless place, a barren slab of blackened volcanic rock and try to grow something on it, without soil, scoured by sun and sea water. No ordinary plant could grow here, yet somehow, despite the extreme conditions, Lichens attach themselves and thrive.

Smoky-eye Boulder Lichen (a crustose lichen)
There are three different lichen types: fruticose (the plant-like ones), folios (the leafy ones; think of the word foliage), and crustose (the crust-like ones). Crustose Lichens most often brave the uninhabitable rock face. You can easily find this type in round patches on the surfaces of boulders or stone walls. These lichens secrete an acid which breaks down solid rock and enables them to attach strongly. This is how primary succession, the process in which bedrock develops into a fully-fledged ecosystem, is jump-started. When the lichens die, their decomposing skeletons create the first layer of dirt. Then mosses come in, grow on the dead lichen, and eventually die themselves. Other plants soon can root on top of the dead moss. Even Linnaeus admitted the importance of Lichens by saying, “though hitherto we have considered theirs a trifling place among plants, nevertheless they are of great importance in that first stage in the economy of nature.” It’s a back-handed compliment, but a compliment nonetheless.

Pixie Cup Lichen (a fruticose lichen)
Unfortunately, it doesn’t seem like much has changed since Linnaeus’s time. When compared to other vegetation and fungi, Lichens have gone unnoticed and are understudied. As an environmental educator, I’ve talked to loads of people who have told me that they had never noticed Lichens until I pointed them out. In addition to their fascinating biology, Lichens serve an important function in the world.  Greenshield Lichens are a crucial part of the nest material for Ruby-throated Hummingbirds, and Prothonotary Warblers use the long, stretchy strands of Bristly Beard Lichen to construct their nests. They are food to slugs, snails, insects, and frogs. Some Lichens absorb air pollutants like sponges, making them indicator species for air quality. These strange organisms are everywhere. We just have to learn to see them.