''Pseudothelomma occidentale'' is a species of

corticolous This glossary of mycology is a list of definitions of terms and concepts relevant to mycology, the study of fungi. Terms in common with other fields, if repeated here, generally focus on their mycology-specific meaning. Related terms can be found ...

(bark-dwelling),

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 ...

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 was first

formally described A species description is a formal scientific description of a newly encountered species, typically articulated through a scientific publication. Its purpose is to provide a clear description of a new species of organism and explain how it differ ...

Albert William Herre Albert William Christian Theodore Herre (September 16, 1868 – January 16, 1962) was an American ichthyologist and lichenologist. Herre was born in 1868 in Toledo, Ohio. He was an alumnus of Stanford University, where he received a Bachelor of ...

in 1910, who initially classified it in the genus ''

Cyphelium ''Cyphelium'' is a genus of crustose areolate lichens with cup-like apothecia filled with sooty black spores.Field Guide to California Lichens, Stephen Sharnoff, Yale University Press, 2014, The genus is in the family Caliciaceae . The genus ha ...

''.

Leif Tibell Leif Tibell (born 16 November 1944) is a Swedish lichenologist and Emeritus Professor at the University of Uppsala. He is known for his expertise on calicioid lichens. He was awarded the Acharius Medal in 2012 for lifetime achievements in lich ...

transferred it to ''

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 ...

'' in 1976. In 2016, María Prieto and Mats Wedin transferred the

taxon In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

to the newly

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 ...

genus '' Pseudothelomma''. In his original description of the lichen, Herre identified ''Cyphelium occidentalis'' as a new species, previously determined as an '' Acolium'' species by Hasse in 1902. He described the

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 ...

as determinate, forming either rounded or oval patches, or spreading extensively, composed of thick with surfaces of many small nodules, creating a deeply fissured, chinky crust of whitish or ashy-grey colour, not reacting to KOH or CaCl₂ tests. The

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

were noted to be innate in swollen warts, varying in size from small to large, with a black and a thick, white, often concealed margin. Herre highlighted its distinctively long, slender

paraphyses Paraphyses are erect sterile filament-like support structures occurring among the reproductive apparatuses of fungi, ferns, bryophytes and some thallophytes. The singular form of the word is paraphysis. In certain fungi, they are part of the f ...

, a broader base marked by a wide, brown-black band, and , strongly constricted spores with an oblong-

ellipsoid An ellipsoid is a surface that can be obtained from a sphere by deforming it by means of directional Scaling (geometry), scalings, or more generally, of an affine transformation. An ellipsoid is a quadric surface; that is, a Surface (mathemat ...

shape. He reported that this species historically grew on old wooden fences in mountainous and foothill regions, although its original habitats had been replaced by wire fencing. The lichen was noted for leaving black marks on the fingers when touched, a characteristic shared with other species within the original genus ''Cyphelium''.

References

Caliciales Lichen species Lichens described in 1910 Taxa named by Albert William Herre {{Caliciales-stub