Background

Lichens are composite organisms made up of a fungal partner or mycobiont and a photosynthetic algal partner, a phycobiont or a photobiont (generally a green algae or cyanobacteria). In rare cases, the fungus may pair with both an algae and cyanobacteria. The two most common photosynthetic organisms to partner with the fungus are Nostoc and Trebouxia a cyanobacteria and algae respectively. When paired, the photobiont and mycobiont appear to be involved in a mutualistic relationship. However, it has been assumed that they may be involved in a controlled parasitism in which the mycobiont enslaves the photobiont for its photosynthesis. The dominant partner in the relationship seemingly appears to be the fungus as the fungi is incapable of producing food on its own. Also, the fungus itself is usually either a parasite or decomposer meaning that it contains parasitic properties. The mycobiant most commonly comes from the kingdom Fungi, while the algal partner comes from the kingdom Protista. In other cases, the fungi will pair with cyanobacteria from the kingdom Monera. The three most common types of lichen are crustose, foliose and fruticose.