[3] He used the name designated by Johann Jacob Dillenius, whose earlier published description did not meet the rules of valid publication as established by the International Code of Nomenclature for algae, fungi, and plants.

However, he did not specify a type specimen; the species Usnea florida, moved to the genus by Friedrich Heinrich Wiggers in 1780, has been designated as the lectotype.

[10][11] Based on a fossil Usnea found in Baltic amber, the genus is known to date back to at least the late Eocene, about 34 million years ago.

[14] Unlike other similar-looking fruticose lichens, species in this genus have an elastic chord or axis running through the middle of the thallus that can be revealed by gently pulling a filament apart from either end.

[23] The National Toxicology Program evaluated the issue,[24] undertaking research involved feeding male and female rats and mice ground Usnea lichens containing usnic acid for three months at various concentrations.

Additionally, both species showed weight loss at elevated exposure levels, and mice exhibited potential genetic damage after two weeks at high concentrations.

[26][27] This wide variety of possible colors can be achieved due to variations in chemical composition depending on the species, locality, and race of a particular specimen.

Specifically, Usnea can contain thamnolic, squamatic, barbatic, salazinic, and alectorialic acids, all of which can affect dye color.

The Tarahumura use them to dye wool blankets in brown and russet hues, and the Mapuche have used Usnea florida to obtain orange.

There is also anthropological evidence that Usnea cocca sonca was historically used for dyeing in Peru, and a lichen called cuaxapaxtle was used near Mexico City.

[31] The northern parula, a species of New World warbler which breeds in North America, uses Usnea lichens in the construction of its nest in some parts of its range.