Illustration of lichen
- lichen 1
1
: any of numerous complex plantlike organisms made up of an alga or a cyanobacterium and a fungus growing in symbiotic association on a solid surface (such as on a rock or the bark of trees)
Note: The main body of the lichen, known as the thallus, is formed by fungal filaments which surround the photosynthetic algal or cyanobacterial cells. The lichen is usually described as having a leaflike (foliose), crusty (crustose), or branching shrub-like (fruticose) form. Lichens often play an important part in the weathering of rocks and include some that are sources of natural dyes.
2
: any of several skin diseases characterized by the eruptions of flat papules
Examples of lichen in a Sentence
Recent Examples on the Web
The lichens are not of concern but can indicate the ligustrum is not making normal growth.
—
Tom MacCubbin, The Orlando Sentinel, 12 July 2025
The researchers say that this discovery could suggest that other exoplanets may contain life similar to the desert lichen.
—Jack Knudson, Discover Magazine, 25 June 2025
To understand how this lichen could survive the UVC radiation, the researchers examined its protective top layer.
—Jack Knudson, Discover Magazine, 25 June 2025
Emperor penguins remain to incubate eggs, while mosses and lichens endure the freeze until the sun returns, the program notes.
—Soo Kim, MSNBC Newsweek, 10 June 2025
See All Example Sentences for lichen
Examples are automatically compiled from online sources to
show current usage.
Read More
Opinions expressed in the examples do not represent those of Merriam-Webster or its editors.
Send us feedback.
Tom MacCubbin, The Orlando Sentinel, 12 July 2025
The researchers say that this discovery could suggest that other exoplanets may contain life similar to the desert lichen.
—Jack Knudson, Discover Magazine, 25 June 2025
To understand how this lichen could survive the UVC radiation, the researchers examined its protective top layer.
—Jack Knudson, Discover Magazine, 25 June 2025
Emperor penguins remain to incubate eggs, while mosses and lichens endure the freeze until the sun returns, the program notes.
—Soo Kim, MSNBC Newsweek, 10 June 2025
See All Example Sentences for lichen
Cite this Entry
“Lichen.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/lichen. Accessed 19 Aug. 2025.
Copy CitationKids Definition
lichen
noun
li·chen
ˈlī-kən 
: any of numerous plantlike living things made up of an alga and a fungus growing together on a solid surface (as a rock or a tree)
Medical Definition
lichen
noun
li·chen
ˈlī-kən
1
: any of several skin diseases characterized by the eruption of flat papules
especially
: lichen planus
2
: any of numerous complex plantlike organisms made up of an alga and a fungus growing in symbiotic association on a solid surface (as a rock)
Love words? Need even more definitions?
Merriam-Webster unabridged
Share