[lahy-kuh
n] 
| 1. | any complex organism of the group Lichenes, composed of a fungus in symbiotic union with an alga and having a greenish, gray, yellow, brown, or blackish thallus that grows in leaflike, crustlike, or branching forms on rocks, trees, etc. |
| 2. | Pathology. any of various eruptive skin diseases. |
| 3. | to cover with or as if with lichens. |
n| li·chen (lī'kən) n.
To cover with lichens. [Latin līchēn, a kind of plant, from Greek leikhēn, from leikhein, to lick; see leigh- in Indo-European roots.] li'chen·ous adj. |
lichen li·chen (lī'kən)
n.
Any of various skin diseases characterized by patchy eruptions of small, firm papules.
| lichen (lī'kən) Pronunciation Key
The mutualistic symbiotic association of a fungus with an alga or a cyanobacterium, or both. The fungal component of a lichen absorbs water and nutrients from the surroundings and provides a suitable environment for the alga or cyanobacterium. These live protected among the dense fungal hyphae and produce carbohydrates for the fungus by photosynthesis. Owing to this partnership, lichens can thrive in harsh environments such as mountaintops and polar regions. The more familiar lichens grow slowly as crusty patches, but lichens are found in a variety of forms, such as the tall, plantlike reindeer moss. The association between the different organisms in a lichen is so close that lichens are routinely referred to as a single organism, and scientists classify lichens using the name of the fungal component. |