''Dolichousnea longissima'' (

syn. The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently. * In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linnae ...

''Usnea longissima''), commonly known by the names old man's beard or Methuselah's beard lichen, is a fruticose lichen in the family

Parmeliaceae The Parmeliaceae is a large and diverse family of Lecanoromycetes. With over 2700 species in 71 genera, it is the largest family of lichen-forming fungi. The most speciose genera in the family are the well-known groups: '' Xanthoparmelia'' ( 822 ...

Description

This lichen is fruticose, with very long stems and short, even side branches. It is considered the longest lichen in the world. The stems are usually 15 to 30 cm in length but are sometimes much longer. It is pale green to silvery-yellow. It has a distinct central cord, which is white. ''D. longissima'' may grow to be 20 feet in length. It predominantly reproduces asexually through fragmentation. Spore-producing structures are rarely observed. It can double its length each year.

Distribution

''Dolichousnea longissima'' is found in boreal forests and coastal woodland in Europe, Asia, and North America. In North America, it is primarily found on the Pacific Coast, and the largest populations are concentrated in the

Pacific Northwest The Pacific Northwest (sometimes Cascadia, or simply abbreviated as PNW) is a geographic region in western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Though ...

. It ranges from Upper Midwest into Canada, the Great Lakes region, and extends to the coast of the Atlantic ocean. It was historically

circumboreal The Circumboreal Region in phytogeography is a floristic region within the Holarctic Kingdom in Eurasia and North America, as delineated by such geobotanists as Josias Braun-Blanquet and Armen Takhtajan. It is the largest floristic region in t ...

, but has been regionally extirpated from areas of Europe and Scandinavia. It has been placed on the Red List of California Lichens, and is considered Endangered in the Norwegian Red List. The species grows within the canopies of coniferous trees, primarily those found in old growth

Douglas fir The Douglas fir (''Pseudotsuga menziesii'') is an evergreen conifer species in the pine family, Pinaceae. It is native to western North America and is also known as Douglas-fir, Douglas spruce, Oregon pine, and Columbian pine. There are three va ...

forests and near bodies of water. Air pollution heavily affects the metabolic functions of the species, and as a result, populations have declined. Industrial logging has also had detrimental impacts on population numbers.

Human use

The species is harvested for decoration. It has also been historically used as a bedding and filtering material. Medicinally, ''D. longissima'' is known as an anti-inflammatory due to the presence of the compound longissiminone. It has been described in Chinese herbal medicine dating back to 500 A.D., where one of the names for the species translates to "pine gauze".

References

{{Taxonbar, from1=Q1809933, from2=Q22111343 Parmelia Lichen species Lichens described in 1810 Taxa named by Erik Acharius Lichens of Asia Lichens of Europe Lichens of North America