What Is a Lichen?

i was just talking to rachel a few minutes ago, and she was not actually aware that a lichen is not a solitary type of organism. It's really one of these things in nature that defiesn our easy understanding of what life even is. What does it mean to be a species? Because we've touched on the the composite aspects of, say, even human biology,. But likeness is like a more pronounced expression of this same idea.