Lichens… What exactly are they?
Lichens are not single organisms. They are in fact a combination of two or three separate organisms that are associated by a symbiotic relationship – a fungus and either an alga, or cyanobacterium (and possibly a yeast). Whilst the independent species (both fungi and algae) may not survive alone, together, they thrive in a mutualistic relationship within large communities. This means that they can survive in habitats that would otherwise be unsuitable, such as wet, humid, or exposed environments.