''Pseudothelomma'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

crustose Crustose is a Habit (biology), habit of some types of algae and lichens in which the organism grows tightly appressed to a substrate, forming a biological layer. ''Crustose'' adheres very closely to the Substrate (biology), substrates at all poin ...

pin lichen Lichens are symbiotic organisms made up of multiple species: a fungus, one or more photobionts (an alga and/or a cyanobacteria) and sometimes a yeast. They are regularly grouped by their external appearance – a characteristic known as their gro ...

s in the family

Caliciaceae The Caliciaceae are a family (taxonomy), family of mostly lichen-forming fungus, fungi belonging to the class (taxonomy), class Lecanoromycetes in the division (mycology), division Ascomycota. Although the family has had its classification chan ...

. It contains two species. The genus was established in 2016 when DNA analysis revealed that two species previously classified in the genus ''

Thelomma ''Thelomma'' is a genus of lichenized fungi in the family Caliciaceae. The genus is widely distributed and contains seven species. ''Thelomma'' was circumscribed by Italian lichenologist Abramo Bartolommeo Massalongo Abramo Bartolommeo Massalo ...

'' were actually distinct and formed their own separate evolutionary group. These lichens are distinguished by their preference for growing on dry, bark-free conifer wood and their black, flat

spore In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...

-bearing structures that may have a greenish-yellow powdery coating.

Taxonomy

Pseudothelomma was

circumscribed In geometry, a circumscribed circle for a set of points is a circle passing through each of them. Such a circle is said to ''circumscribe'' the points or a polygon formed from them; such a polygon is said to be ''inscribed'' in the circle. * Circum ...

in 2017 by the lichenologists Maria Prieto and Mats Wedin. Molecular analyses of a five–locus data set showed that the wood-dwelling lichens long treated as ''Thelomma ocellatum'' and ''T. occidentale'' do not nest with ''

'' in the strict sense (''sensu stricto'') (a coastal, saxicolous lineage), but instead form their own well-supported

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

within the family

. To accommodate this lineage, Maria Prieto and Mats Wedin erected the new genus ''Pseudothelomma'', designating ''P. ocellatum'' (originally described as ''Acolium ocellatum'' in 1861) as the

type species In International_Code_of_Zoological_Nomenclature, 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 spe ...

and transferring ''T. occidentale'' as ''P. occidentale''. The generic name refers to the superficial resemblance to ''Thelomma'' while signalling its distinct phylogenetic position. Phylogenetically, ''Pseudothelomma'' belongs to a lineage that also contains ''Tholurna dissimilis'' and the stalked genus ''

Allocalicium ''Allocalicium'' is a single-species fungal genus in the family Caliciaceae. It is monotypic, containing the single pin lichen species ''Allocalicium adaequatum''. This lichen occurs in North America, South America, Europe, and the Russian Far ...

'', but it is readily separated from those taxa by its thin, crystal-free cortex, immersed apothecia with a laterally very thin excipulum, and by its preference for dry, decorticated conifer wood rather than rock or bark substrates. The genus currently contains two accepted species both characterised by black, flat mazaedia that may carry a greenish-yellow pruina and by one-septate, dark brown spores. Occasional production of usnic acid in the thallus and epanorin or rhizocarpic acid in the hymenium further distinguishes the group within the family.

Description

''Pseudothelomma'' has a

thallus Thallus (: 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. A thallus usually names the entir ...

that is

, and grey, with a thin

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 ...

. The

ascomata An ascocarp, or ascoma (: ascomata), is the fruiting body (sporocarp (fungi), sporocarp) of an ascomycete phylum fungus. It consists of very tightly interwoven hyphae and millions of embedded ascus, asci, each of which typically contains four to ...

are immersed in wrinkles, and are flat, sometimes with a green or yellow

pruina Pruinescence , or pruinosity, is a "frosted" or dusty-looking coating on top of a surface. It may also be called a pruina (plural: ''pruinae''), from the Latin word for hoarfrost. The adjectival form is pruinose . Entomology In insects, a "bloom" ...

on the mazaedia. The

spores In biology, a spore is a unit of sexual (in fungi) or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plant ...

have a single

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

and are black-brown. Secondary chemicals found in ''Pseudothelomma'' include

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 and 1937 by Frank H. Curd and Al ...

in the thallus (occasionally), and epanorin and

rhizocarpic acid Rhizocarpic acid is an organic compound with the molecular formula C28H23NO6 which has been isolated from the lichen ''Rhizocarpon geographicum'' and other lichens A lichen ( , ) is a hybrid colony (biology), colony of algae or cyanobacteri ...

in 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 oth ...

and

mazaedium This glossary provides an overview of scientific terminology, terms used in the description of lichens, composite organisms arising from algae or cyanobacteria living symbiosis, symbiotically among Hypha, filaments of multiple fungus species. Er ...

Species

*'' Pseudothelomma occidentale'' *'' Pseudothelomma ocellatum''

References

{{Taxonbar, from=Q105409877 Caliciales Caliciales genera Lichen genera Taxa described in 2016 Taxa named by Mats Wedin