Carol Pinnell-Alison  |  10/7/2010 7:27:08 PM

Lichen is shown on a tree trunk depicting the crustose, foliose and fructicose forms.

Lichen on a fence post.

Lichen on bricks.

Lichen is a perennial organism consisting of a fungus and a green or blue-green alga. The two organisms have a symbiotic relationship in which the fungus receives 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 hairlike.

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.


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