''Usnochroma'' 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 ...

lichen A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

in the family

Teloschistaceae The Teloschistaceae are a large family of mostly lichen-forming fungi belonging to the class Lecanoromycetes in the division Ascomycota. The family, estimated to contain over 1800 species, was extensively revised in 2013, including the creation o ...

. It has two species of

crustose lichen Crustose lichens are lichens that form a crust which strongly adheres to the Substrate (biology), substrate (soil, rock, tree bark, etc.), making separation from the substrate impossible without destruction. The basic structure of crustose lichen ...

s. The genus was

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 ...

in 2013 by lichenologists Ulrik Søchting, Ulf Arup, and Patrik Frödén, with ''Usnochroma carphineum'' assigned as the

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 ...

. The genus name refers to the yellowish-green colour of the

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 ...

, which is caused by the substance

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 ...

. ''Usnochroma'' species occur in Macaronesia, South Africa, the

Mediterranean Basin In biogeography, the Mediterranean Basin (; also known as the Mediterranean Region or sometimes Mediterranea) is the region of lands around the Mediterranean Sea that have mostly a Mediterranean climate, with mild to cool, rainy winters and w ...

, and

Algeria ) , image_map = Algeria (centered orthographic projection).svg , map_caption = , image_map2 = , capital = Algiers , coordinates = , largest_city = capital , relig ...

Description

''Usnochroma'' has a crust-like

that is pale yellow in colour. It does not contain anthraquinones, compounds often responsible for the yellow and orange colours in many lichens of the Teloschistaceae. The outer layer, or cortex, occurs in one of two tissue structures: or . The reproductive structures, known as apothecia, are in form, characterized by a very thin outer edge and a rusty orange-coloured central . The spores of this genus are distinctive, being with an elongated partition, or

septum In biology, a septum (Latin for ''something that encloses''; plural septa) is a wall, dividing a cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Human anatomy * Interatri ...

. There is no observed presence of pycnidia, another type of reproductive structure. The thallus contains

and

gyrophoric acid Gyrophoric acid is a depside that can be found in the lichen ''Cryptothecia rubrocincta'' and in ''Xanthoparmelia pokomyi''. It can also be found in most of the species of the '' Actinogyra'', ''Lasallia'', and ''Umbilicaria'' genera Genus ( p ...

. In addition to these, the apothecia contain parietin. '' Buellia badia'' and '' Tremella caloplacae'' are

lichenicolous fungi A lichenicolous fungus is a parasitic fungus that only lives on lichen as the host. A lichenicolous fungus is not the same as the fungus that is the component of the lichen, which is known as a lichenized fungus. They are most commonly specific to ...

that have been recorded parasitising ''Usnochroma carphinea''.

Species

* '' Usnochroma carphineum'' * '' Usnochroma scoriophilum''

References

{{Taxonbar, from=Q25935102 Teloschistales Teloschistales genera Taxa described in 2013 Taxa named by Ulf Arup Taxa named by Ulrik Søchting Taxa named by Patrik Frödén