County Ag News

What are lichens?


I receive a number of calls from homeowners concerned that their trees are infected with a disease when it is really a lichen they are seeing. Lichens appear very much like a fungal growth when they are found on trees

A lichen looks like a single organism, but it is actually a symbiotic relationship between different organisms. It is composed of a fungal partner (mycobiont) and one or more photosynthetic partners (photobiont). The photosynthetic partner is generally green algae or cyanobacteria. There are about 13,500 species of lichen on the Earth.

Lichens may be found growing on tree trunks and branches, on headstones at graveyards and on machinery that is sitting outside. A lichen absorbs its mineral nutrients from the air and rainfall. Lichens are only using the spot where they are growing as a resting site. They don’t obtain any water or nutrients from the host site and therefore don’t do any damage to trees where they may be found.