Lichens have a very particular character: they are double, even sometimes triple beings since they are formed from the very close association (or symbiosis) between a fungus and a microscopic partner capable of carrying out photosynthesis, i.e. a green algae, or a cyanobacterium (or sometimes both together!).
The study of lichens is no longer a matter of botany but of mycology and it is not just a question of words: to really understand and study lichens, you have to know fungi deeply.