The plant-like appearance of lichens hides their true identity. A lichen is not a single organism, but the result of a partnership (mutualistic symbiosis) between a fungus and an alga or cyanobacteria. Some lichens are formed of three or more partners. The body of a lichen consists of fungal filaments (hyphae) surrounding cells of green algae and/or blue-green cyanobacteria. The basis of the mutualistic symbiosis in lichens is similar to the mycorrhizal partnership between some species of fungi and the roots of most plants. The lichen fungus provides its partner(s) a benefit (protection) and gains nutrients in return.
The complexity of lichen partnerships has caused lichens to be described as "small ecosystems". They are classified as members of the Fungus Kingdom by systematists because the fungus partner is always the major partner. After a lichen symbiosis is established, the fungus has the greatest influence on the final form of the lichen body’s shape, and whether it is tough or flexible. The algal and bacterial partner(s) each have their own scientific names, but the lichen symbiosis is known only by the name of its fungus.
Cross Section of Lichen.