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
Cite this Entry
“Lichen.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/lichen. Accessed 1 Sep. 2026.
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