Lichens are composite organisms, not individual organisms. They do not form a taxonomic group, but are found in separate lineages. They are composed of a fungus (the mycobiont) and a photosynthetic partner (the photobiont), usually either a green alga or a cyanobacteria. They take their scientific name from the fungal component. There are 14,000 to 20,000 species of lichens in hundreds of genera.