what is mode of nutrition of lichens?some examples of lichens?

Lichens are the organisms that are formed by the symbiotic relationship or association of the fungus and the green algae or cyanobacteria. The algae produces food for fungi and itself whereas fungi helps in attachment and absorption of nutrients from substrate. They are slow-growing and typically forms a low crust-like or leaf-like branching growth on rocks, walls, and trees. For example, most of the fungi of group ascomycota form association with algae of groups like cyanobacteria, chlorophyta etc.