As I stand on a forested hillside, I run my hand over the trunk of a large Douglas-fir tree. Beneath my fingers is not tree bark, but a layer of brilliant yellow-green material. This is not a plant, though it looks a bit like one, but a lichen, a unique organism that is a combination of fungi and algae. Amazingly, it is growing here with no soil, no roots, and only scanty water. I look up, and above, hair-like lichens hang gracefully from the branches. Beside me, brightly coloured crusts of lichens cling to the surface of a boulder. They seem barely alive, and yet they are. The closer I look, the more lichens I find everywhere.
Lichens, as I said above, are not plants (despite sometimes being included in field guides to plants): they are composed of fungi and algae (often bacteria as well), a combination as bizarre as a plant and an animal forming parts of a single organism. The algae are photosynthesizers, and so can use sunlight to supply their fungal partners with carbohydrates, while the fungi protect the algae from the environment and absorb the water and nutrients that the algae need to survive. This combination of fungi and algae creates an entirely new organism – a lichen – that is more than the sum of its parts, that can evolve, sustain itself, and interact with other members of its ecosystem.
Lichens have existed for hundreds of millions of years, and many thousands of different kinds exist. They grow almost everywhere – on the surfaces of rocks, on the bark of trees, spreading in mats over the ground. They can grow in places that are too dry, hot, or cold for anything else to grow, including some of our harshest climates, such as on mountaintops and in the Arctic and Antarctic. In the hot, dry environment of grasslands, lichens form part of the cryptogamic crust, which covers the ground between grasses and helps to protect the soil from erosion and conserve moisture. And on rocky seashores, black tar lichens – one of the few lichens that can grow in salty conditions – cling to the rocks in the upper intertidal zone.
Lichens are often the first organisms to colonize a new piece of land, such as rock exposed after the retreat of glaciers. These thin, crust-like lichens are known, appropriately, as crustose lichens. Over many years, even centuries, of growing on the rock, the crustose lichen may begin to build up a tiny bit of soil and moisture around itself, and a larger lichen, moss, or flowering plant may eventually be able to grow in that, as what was once a bare rock is transformed into a piece of land where a diversity of life can flourish.
If we are open to observing and learning from the lichens, they can teach us about patterns in the world around us that we might otherwise be unaware of. For example, some crustose lichens only grow on rocks where they have a source of calcium or nitrates. These nutrients often come from bird droppings or mammal urine, so these brightly coloured lichens may indicate that the rock is often used as a perch by a bird or small mammal. Another species, lungwort (Lobaria pulmonaria; below photo), grows in forests where it helps to turn nitrogen in the atmosphere into nitrates that plants need. However, it only grows in areas with clean air, and will die off in polluted areas. This lichen (and others) can thus be used as indicator of air quality. If you see this beautiful lichen growing on the trees, then you know that you can literally breathe easier!
When we think of nature, we usually picture towering trees and large, charismatic mammals. Most lichens, however, are relatively small and inconspicuous. To notice them and to learn from them, we have to train ourselves to see them, and to look for those small details that fill our everyday lives. Lichens have made me a better observer. By looking for them, I slow down and notice much more than just the lichens. And by looking for these small details, I find more contentment in my everyday life. I love lichens because they are not fungi, not algae, but something in between. I love them because they can live in such marginal habitats. I love them because they grow in my own backyard, and yet few people see them. I love them because, in a way, they live at the edge of the ordinary, and they invite us to explore that edge as well.