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
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
Was this blemish somewhat new, or had it, like the rest of the decay in her life—the age spots that bloomed like lichen across the top of her hands, the foreshortening plait of her spine—been stealthily creeping up on her?
—Literary Hub, 9 July 2025
The key to determining which planets could host extraterrestrial life could be growing in the harshest deserts of Earth in the form of lichen.
—Robert Lea, Space.com, 26 June 2025
See All Example Sentences for lichen
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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
Was this blemish somewhat new, or had it, like the rest of the decay in her life—the age spots that bloomed like lichen across the top of her hands, the foreshortening plait of her spine—been stealthily creeping up on her?
—Literary Hub, 9 July 2025
The key to determining which planets could host extraterrestrial life could be growing in the harshest deserts of Earth in the form of lichen.
—Robert Lea, Space.com, 26 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 6 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)
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