Hypertext Webster Gateway: "lichen"
From Webster's Revised Unabridged Dictionary (1913) (web1913)
Lichen \Li"chen\ (l[imac]"k[e^]n; 277), n. [L., fr. Gr.
leichh`n.]
1. (Bot.) One of a class of cellular, flowerless plants,
(technically called {Lichenes}), having no distinction of
leaf and stem, usually of scaly, expanded, frond-like
forms, but sometimes erect or pendulous and variously
branched. They derive their nourishment from the air, and
generate by means of spores. The species are very widely
distributed, and form irregular spots or patches, usually
of a greenish or yellowish color, upon rocks, trees, and
various bodies, to which they adhere with great tenacity.
They are often improperly called {rock moss} or {tree
moss}.
Note: A favorite modern theory of lichens (called after its
inventor the Schwendener hypothesis), is that they are
not autonomous plants, but that they consist of
ascigerous fungi, parasitic on alg[ae]. Each lichen is
composed of white filaments and green, or greenish,
rounded cells, and it is argued that the two are of
different nature, the one living at the expense of the
other. See {Hyph[ae]}, and {Gonidia}.
2. (Med.) A name given to several varieties of skin disease,
esp. to one characterized by the eruption of small,
conical or flat, reddish pimples, which, if unchecked,
tend to spread and produce great and even fatal
exhaustion.
From WordNet (r) 1.7 (wn)
lichen
n 1: any of several eruptive skin diseases characterized by hard
thick lesions grouped together and resembling lichens
growing on rocks
2: any thallophytic plant of the division Lichenes; occur as
crusty patches or bushy growths on tree trunks or rocks or
bare ground etc.
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