A Role Model of Super Cooperation: Lichen

 We've probably all noticed lichen when we're out in Nature, or even right outside our homes. They're humble things, not demanding much of our attention. But we often see them on the trunks of trees or on smooth rock faces. The fascinating thing to me about lichens is that they are a perfect example of two entirely different beings coming together to make one organism. And there are over 13,000 species of lichen! When they found each other, they didn't stop, but expanded into so many, many forms.

Fungi are the dominant partner of this duo. About 80% of the lichen body is made up of the fungus. But fungus have a hard time  making food without help. So they often join with a green algae or cyanobacteria, both of whom use photosynthesis to translate sun energy into nourishment. These different organisms join together in a symbiotic relationship that benefits both parties.

There are three main forms of lichen: Crustase (like crust), Foliose (like leaves), and Friticose (tube or bead-like strands). Lichen are slow-growing, and they need lots of sun to thrive. The smooth bark of young trees tends to be good for Crustase lichen. Once tree bark gets more uneven and striated, the other two lichen (Foliose and Friticose) move in. There seems to be no particular species of trees that lichen prefer. But they do need sun, so the places on a trunk (or rock or somewhere else) that gets the most sun is the happiest place for lichen. Often they grow on dead or dying branches because there are no leaves to get in the way of sunlight. And they tend to grow less frequently on conifers because the constant foliage shades the bark from the sun.

People often wonder if the presence of lichen on the bark of a tree is a danger to the tree. Should they try to scrape the lichen off to protect the tree? The answer, I found, is that lichen do not hurt a tree, and you would probably hurt the tree if you tried to get lichen off its bark. Once a branch is dead, fungi can penetrate the wood and help it decompose. But no need to worry about lichen hurting anything. In fact, the presence of lichen is an indicator of good air quality. Lichen are very sensitive to polluted air, kind of like the canary in the coal mine. So we can be glad when we see lichen!

Reproduction of lichen starts with a fungus producing millions of spores. When some of these come into contact with the appropriate algae or cyanobacteria, the symbiotic relationship that creates lichen can happen. Lichen can also multiply on its own if a chunk of it is broken off and ends up in a sunny spot. Then that piece continues to grow.

Does the ecosystem benefit from having lichen in it? The deer would say a resounding yes, for they eat it. Birds use it to construct nests. Even humans have eaten lichen when food is scarce, though I wouldn't recommend going out to the woods to munch on it. Some are known to be at least somewhat toxic, and with 13,000 species, it might be hard to choose the right one!

What fascinates me about lichen has to do with the symbiotic relationship. Two totally different life forms somehow found that together they made a more successful life than separately. Somewhere back in the history of evolution on this planet, these organisms stumbled upon each other, found that they were better off together, and made a whole new addition to the botanical world. Hooray for them!