Lichens are very complex. There is a symbiosis, but I can't remember the names of the two components. I'll have to try searching.

Here is URL: http://www.ucmp.berkeley.edu/fungi/lichens/lichens.html

Lichens are unusual creatures. A lichen is not a single organism the way most other living things are,
but rather it is a combination of two organisms which live together intimately. Most of the lichen is
composed of fungal filaments, but living among the filaments are algal cells, usually from a green alga
or a cyanobacterium.

In many cases the fungus and the alga which together make the lichen may each be found living in
nature without its partner, but many other lichens include a fungus which cannot survive on its own --
it has become dependent on its algal partner for survival. In all cases though, the appearance of the fungus in the lichen is quite
different from its morphology as a separately growing individual.

The true identity of lichens as symbiotic associations of two different organisms was first proposed by Beatrix Potter, who is
best remembered for her children's books about Peter Rabbit. In addition to her books, she spent time studying and drawing
lichens. Her illustrations are still appreciated for their detailed and accurate portrayal of the delicate beauty of these bizarre
organisms.