Lichens are a combination of fungus and algae that work together through symbiosis and mutualism to survive. The fungi protect the algae while the algae acts as a food source for the fungi. There are three main types of lichen, crustose, foliose, and fruticose. Crustose can be identified by its crusty texture, foliose can be identified by its clover shaped edges, and fruticose can be identified by its shrub like texture. You can often find lichens in the forest on trees and stones. Lichens are able to withstand extreme conditions but are sensitive to disturbances in the environment. Lichens are able to adapt to conditions by slowing down their metabolic rate which slows their overall growth.