''Dolichousnea'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

fruticose lichen A fruticose lichen is a form of lichen fungi that is characterized by a coral-like shrubby or bushy growth structure. It is formed from a symbiotic relationship of a photobiont such as green algae or less commonly cyanobacteria and one, two or mor ...

s 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 ...

. It has three species. The widely distributed

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

, ''

Dolichousnea longissima ''Dolichousnea longissima'' ( syn. ''Usnea longissima''), commonly known by the names old man's beard or Methuselah's beard lichen, is a fruticose lichen in the family Parmeliaceae. Description This lichen is fruticose, with very long stems and ...

'', is found in

boreal Boreal may refer to: Climatology and geography *Boreal (age), the first climatic phase of the Blytt-Sernander sequence of northern Europe, during the Holocene epoch *Boreal climate, a climate characterized by long winters and short, cool to mild ...

regions of Asia, Europe, and North America.

Taxonomy

''Dolichousnea'' was originally

circumscribed In geometry, the circumscribed circle or circumcircle of a polygon is a circle that passes through all the vertices of the polygon. The center of this circle is called the circumcenter and its radius is called the circumradius. Not every polyg ...

as a

subgenus In biology, a subgenus (plural: subgenera) is a taxonomic rank directly below genus. In the International Code of Zoological Nomenclature, a subgeneric name can be used independently or included in a species name, in parentheses, placed between t ...

of the large genus ''

Usnea ''Usnea'' is a genus of mostly pale grayish-green fruticose lichens that grow like leafless mini-shrubs or tassels anchored on bark or twigs.Field Guide to California Lichens, Stephen Sharnoff, Yale University Press, 2014, The genus is in the f ...

'', by Japanese lichenologist Yoshihito Ohmura in 2001. He considered that it was possible to treat the three taxa as a genus, but thought it more suitable to treat ''Dolichousnea'' at the rank of subgenus, because the taxa have the

synapomorphies In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...

of the genus ''Usnea'': a fruticose thallus, a central cartilaginous axis throughout the thallus, and the presence of

usnic acid Usnic acid is a naturally occurring dibenzofuran derivative found in several lichen species with the formula C18H16O7. It was first isolated by German scientist W. Knop in 1844 and first synthesized between 1933-1937 by Curd and Robertson. Usnic a ...

in the cortex. In 2004, Kristina Articus proposed to raise the subgenus to generic rank, a decision that was accepted in later analyses.

Description

''Dolichousnea'' lichens have a pendent

thallus Thallus (plural: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. Many of these organisms wer ...

, in which all the branches hang downward. The branching is isotomic-dichotomous, meaning that the thallus divides into isotomic (i.e. dividing a line at points equally distant from its opposite ends) branches of more or less equal thickness. One of the characteristics of ''Dolichousnea'' are the presence of annular-pseudocyphellae between segments. These are pseudocyphellae that resemble annular cracks, but the space between segments is swollen and surrounded by maculae (white spots on branch surface that form when the

cortex Cortex or cortical may refer to: Biology * Cortex (anatomy), the outermost layer of an organ ** Cerebral cortex, the outer layer of the vertebrate cerebrum, part of which is the ''forebrain'' *** Motor cortex, the regions of the cerebral cortex i ...

tissue is thin). These pseudocyphellae differ from physical cracks, and seem to be formed due to pressure from the medullary hyphae beneath the cortex. ''Dolichousnea'' has a thicker hypothecium (a layer of dense

hypha A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one or ...

l tissue just below the

hymenium The hymenium is the tissue layer on the hymenophore of a fungal fruiting body where the cells develop into basidia or asci, which produce spores. In some species all of the cells of the hymenium develop into basidia or asci, while in others some ...

) than other subgenera of ''Usnea'', typically measuring 100–160 μm; in contrast, subgenera ''Usnea'' and ''Eumitria'' range over 30–60 μm. Another characteristic of ''Dolichousnea'' is a positive iodine reaction in its axis.

Species

*''

Dolichousnea diffracta ''Dolichousnea'' is a genus of fruticose lichens in the family Parmeliaceae. It has three species. The widely distributed type species, ''Dolichousnea longissima'', is found in boreal ecosystem, boreal regions of Asia, Europe, and North America. ...

'' – East Asia *''

'' – boreal regions of Asia, Europe, North America *''

Dolichousnea trichodeoides ''Dolichousnea'' is a genus of fruticose lichens in the family Parmeliaceae. It has three species. The widely distributed type species, ''Dolichousnea longissima'', is found in boreal regions of Asia, Europe, and North America. Taxonomy ''Dolich ...

'' – East Africa; Asia; Australia; Europe Recent (2020)

molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

analysis suggests that the taxon ''Dolichousnea trichodeoides'' represent an unresolved

species complex In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...

References

Cited literature

* {{Taxonbar, from=Q21221542 Parmeliaceae Lecanorales genera Lichen genera Taxa described in 2001