| usnea | <botany> A genus of lichens, most of the species of which have long, gray, pendulous, and finely branched fronds. Usnea barbata is the common bearded lichen which grows on branches of trees in northern forests. Origin: NL, from Ar. Usnah moss. Source: Websters Dictionary (01 Mar 1998) |
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| usnic | <chemistry> Pertaining to, or designating, a complex acid obtained, as a yellow crystalline substance, from certain genera of lichens (Usnea, Parmelia, etc). Source: Websters Dictionary (01 Mar 1998) |
| usnic acid | An organic acid extracted from the lichen Usnea barbata whichhas antibiotic properties, particularly against Gram-positive bacteriasuch at M. Tuberculosis as well as some pathogenic fungi. (09 Oct 1997) |