Lichens are perennial organisms consisting of a fungus and a green alga or blue-green bacterium. The two organisms have a symbiotic relationship where the fungus receives some food from the alga through photosynthesis and the alga obtains water, minerals and protection from the fungus.
The body of the lichen is called a thallus and can have several forms. The thalli may be crustose or appressed to the substrate, foliose with leaflike lobes borne above the substrate or fructicose linear, fingerlike or hair like.
Lichens reproduce vegetatively and are spread by wind or water. They do not have roots so they can be found on many substrates including the trunks of trees, shrubs, rocks and fence posts. Lichens do not harm plants but do compete with plants for light.
Lichens have been used in making dyes, perfumes and traditional medicines.
Lichen found on brick.
Lichen found on tree trunk.
The LSU AgCenter and the LSU College of Agriculture