''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 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, 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

pseudocyphella Pseudocyphellae (singular ''pseudocyphella'') are structures in lichens that appear as tiny pores on the outer surface (the cortex of the lichen. They are caused when there is a break in the cortex of the lichen, and the medullary hyphae extend t ...

e 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 tissue is thin). These pseudocyphellae differ from physical cracks, and seem to be formed due to pressure from the

medullary Medulla or Medullary may refer to: Science * Medulla oblongata, a part of the brain stem * Renal medulla, a part of the kidney * Adrenal medulla, a part of the adrenal gland * Medulla of ovary, a stroma in the center of the ovary * Medulla of ...

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 The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...

; 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'' – East Asia *'' Dolichousnea longissima'' – boreal regions of Asia, Europe, North America *'' Dolichousnea trichodeoides'' – 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.

References

Cited literature

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