Usnea

Usnea is a genus of fruticose lichens, often called beard lichens, whose branching, hairlike thalli commonly hang from trees or grow on rocks.

Lichen: A stable association between a fungus and photosynthetic partners, usually algae or cyanobacteria. Usnea is a lichen whose fungal partner builds the visible beardlike body.
Alectorialic acid: A lichen secondary metabolite found in some species, including members of Usnea. Its presence can help distinguish certain Usnea species during chemical identification.
Lichen bioindicator: A lichen used to infer environmental conditions from its presence, abundance, or chemistry. Usnea’s sensitivity to air pollution makes its occurrence useful in some monitoring programs.
Bryoria: A genus of filamentous fruticose lichens that often grows in hanging strands on trees. Bryoria can resemble Usnea, but its thalli lack Usnea’s characteristic elastic central cord.
Fruticose lichen: A lichen growth form with a branched, three-dimensional thallus, often shrubby or hanging. This growth form gives Usnea its dangling, finely branched appearance.
Soredium: A powdery lichen propagule containing fungal hyphae and photosynthetic cells. Some Usnea species reproduce vegetatively through soredia that disperse both partners together.
Air pollution: Contamination of the atmosphere by harmful substances or excessive concentrations of natural substances. Many Usnea species decline where airborne pollutants impair their growth.
Alectoria: A genus of shrubby or hanging fruticose lichens, chiefly found on trees and rocks. Alectoria is another beardlike genus that can be confused with Usnea in the field.
Mycobiont: The fungal partner in a lichen association. The mycobiont forms most of Usnea’s thallus and determines its fungal identity.
Isidium: A small outgrowth of a lichen thallus containing fungal and photosynthetic cells. Isidia provide another way some Usnea species spread intact lichen partnerships.

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