''Usnea'' is a genus of mostly pale grayish-green fruticose

lichen A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.shrub A shrub (often also called a bush) is a small-to-medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees ...

s or tassels anchored on bark or twigs.Field Guide to California Lichens, Stephen Sharnoff, Yale University Press, 2014, The genus is in the family Parmeliaceae. It grows all over the world. Members of the genus are commonly called old man's beard, beard lichen, or beard moss. Like other lichens it is a symbiosis of two or three fungi and an alga. In ''Usnea'', the fungus belongs to the division Ascomycota, while the alga is a member of the division Chlorophyta. Members of the genus are similar to those of the genus ''Alectoria (fungus), Alectoria''. A distinguishing test is that the branches of ''Usnea'' are somewhat elastic, but the branches of ''Alectoria'' snap cleanly off.

Systematics

The genus ''Usnea'' was circumscribed by Michel Adanson in 1763. He used the name designated by Johann Jacob Dillenius, whose earlier published description did not met 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. Since then, hundreds of species have been described. A three-volume series by Józef Motyka published in 1936 and 1947 listed 451 species. By 2006, the genus contained more than 600 species, which made it one of the largest genera within the family Parmeliaceae. However, many former species are now regarded as morphology (biology), morphological varieties and adaptations to local circumstances. The number of recognized species in Finland has decreased for this reason, for example, dropping from 34 in 1951 to 25 in 1963 and only 12 in 2000. In addition, some former ''Usnea'' species have been moved to other genera; for instance, ''Usnea longissima'' was renamed ''Dolichousnea longissima'' in 2004. By 2022, the overall number of species assigned to the genus had dropped to 355. The name ''Usnea'' is probably derived from the Arabic word ''Ushnah'', meaning moss or lichen, though it may also mean "rope-like". 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.

Morphology and reproduction

As a fruticose lichen, ''Usnea'' appears as a shrub-like growth on host trees. 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. It reproduces via vegetative reproduction, vegetative means through fragmentation (reproduction), fragmentation, asexual reproduction, asexual means through soredium, soredia, or sexual reproduction, sexual means through ascogonium and spermatogonium. The growth rate of lichens in nature is slow, but the growth rate has been sped up in laboratory conditions where ''Usnea'' is being cultured. ''Usnea'' looks very similar to the plant Spanish moss, so much so that the latter's Latin name is derived from it (''Tillandsia usneoides'', the 'Usnea-like Tillandsia').

Ecology

Like other lichens, ''Usnea'' often grows on sick or dying trees due to the pre-existing loss of canopy leaves, allowing for greater photosynthesis by the lichen's algae; this leads some gardeners to mistakenly blame the lichen for the tree's leaf loss and illness. ''Usnea'' is very sensitive to air pollution, especially sulfur dioxide. Under poor growing conditions, such as areas high in pollution, they may grow no larger than a few millimetres, if they survive at all. Where the air is unpolluted, they can grow to 10–20 cm long. It can sometimes be used as a bioindicator, because it tends to only grow in those regions where the air is clean, and of high quality.

Uses

Medical claims

According to Paul Bergner, Author of Medical Herbalism. "The usnic acid in ''Usnea'' is effective against gram positive bacteria such as ''Streptococcus'' and ''Staphylococcus'', making ''Usnea'' a valuable addition to herbal formulas for sore throats and skin infections. It is also effective against a bacterium that commonly causes pneumonia" There is reason to believe that ''Usnea'', in high concentrations, could possess some toxicity. The National Toxicology Program is currently evaluating the issue.

Dyes

''Usnea'' species have been used to create orange, yellow, green, blue, and purple dyes for textiles.

Cosmetics

''Usnea barbata'' has been used in cosmetic production for its antimicrobial and antifungal properties as a preservative and deodorant.

Combustible

''Usnea barbata'' when dry is extremely flammable and is often used as a firestarter.

Species

*''Usnea acromelana'' *''Usnea alboverrucata'' *''Usnea amblyoclada'' *''Usnea angulata'' *''Usnea antarctica'' *''Usnea aranea'' *''Usnea articulata'' *''Usnea aurantiaciparvula'' *''Usnea austrocampestris'' – Falkland Islands *''Usnea bismolliuscula'' *''Usnea boomiana'' *''Usnea brattiae'' *''Usnea cavernosa'' *''Usnea cedrosiana'' *''Usnea ceratina'' *''Usnea chaetophora'' *''Usnea cirrosa'' *''Usnea clerciana'' *''Usnea confusa'' *''Usnea cornuta'' *''Usnea crenulata'' *''Usnea crocata'' *''Usnea cylindrica'' *''Usnea diplotypus'' *''Usnea effusa'' *''Usnea elata'' *''Usnea elixii'' *''Usnea esperantiana'' *''Usnea exigua'' *''Usnea filipendula'' *''Usnea firmula'' *''Usnea flammea'' *''Usnea flavocardia'' *''Usnea flavorubescens'' *''Usnea fleigiae'' *''Usnea florida'' *''Usnea floriformis'' *''Usnea foveata'' *''Usnea fragilescens'' *''Usnea fulvoreagens'' *''Usnea galapagona'' *''Usnea geissleriana'' *''Usnea glabrata'' *''Usnea glabrescens'' *''Usnea glauca'' *''Usnea grandisora'' *''Usnea grandispora'' *''Usnea himantodes'' *''Usnea hirta'' *''Usnea inermis'' *''Usnea intermedia'' *''Usnea kalbiana'' *''Usnea krogiana'' *''Usnea lambii'' *''Usnea lapponica'' *''Usnea leana'' *''Usnea lutii'' *''Usnea macaronesica'' *''Usnea maculata'' *''Usnea marivelensis'' *''Usnea mayrhoferi'' *''Usnea mekista'' *''Usnea messutiae'' *''Usnea molliuscula'' *''Usnea myrmaiacaina'' *''Usnea neuropogonoides'' *''Usnea nidifica'' *''Usnea nidulifera'' *''Usnea oncodeoides'' *''Usnea oncodes'' *''Usnea oreophila'' *''Usnea pacificana'' *''Usnea pallidocarpa'' *''Usnea parafloridana'' *''Usnea patriciana'' *''Usnea pendulina'' *''Usnea perplexans'' *''Usnea poliothrix'' *''Usnea praetervisa'' *''Usnea propagulifera'' *''Usnea pulvinata'' *''Usnea pycnoclada'' *''Usnea pygmoidea'' *''Usnea quasirigida'' *''Usnea ramulosissima'' *''Usnea roseola'' *''Usnea rubicunda'' *''Usnea rubricornuta'' *''Usnea rubriglabrata'' *''Usnea rubrotincta'' *''Usnea sanguinea'' *''Usnea saxidilatata'' *''Usnea scabrata'' *''Usnea scabrida'' *''Usnea silesiaca'' *''Usnea subalpina'' *''Usnea subaranea'' *''Usnea subcapillaris'' *''Usnea subcomplecta'' *''Usnea subcornuta'' *''Usnea subdasaea'' *''Usnea subeciliata'' *''Usnea subflammea'' *''Usnea subflaveola'' *''Usnea subfloridana'' *''Usnea subglabrata'' *''Usnea subparvula'' *''Usnea subrubicunda'' *''Usnea subscabrosa'' *''Usnea tamborensis'' *''Usnea taylorii'' *''Usnea torulosa'' *''Usnea trachycarpa'' *''Usnea ushuaiensis'' *''Usnea viktoriana'' *''Usnea vrieseana'' *''Usnea wasmuthii'' *''Usnea xanthopoga''

References

Sources

* * * * * * * * * * * {{Taxonbar, from=Q121799 Usnea, Parmeliaceae Lichen genera Lecanorales genera Taxa described in 1763 Taxa named by Michel Adanson