There exists a close association between the alga and the fungus within a lichen. The fungus:

Lichens are unique, double organisms that consist of two unrelated components, an alga and/ or cyanobacterium (photobiont) and a fungus (mycobiont). Lichens are unique, double organisms that consist of two unrelated components, an alga and/or cyanobacterium (photobiont) and a fungus (mycobiont) Related Theory Lichens have a body called a thallus, an outer, tightly packed fungal layer called a cortex, and an inner, loosely packed fungal layer called a medulla. Lichens use hyphal bundles called rhizines to attach to the substrate.