''Pachyascus'' is the sole

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 ...

in the family Pachyascaceae. It contains a single species, the

lichen A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.Josef Poelt Josef Poelt was a botanist, bryologist and lichenologist. He held the chair in Systematic Botany and Plant Geography at the Free University of Berlin (1965 - 1972) and then was head of the Botanical Institute and Botanical Garden of Graz Universi ...

and

Hannes Hertel Hannes Hertel is a German botanist and taxonomist and was Director of the State Herbarium in Munich, Germany 1992 - 2004. His specialist areas are the fungi and lichens. Early life and education Hannes Hertel was born in 1939. His doctorate was ...

. ''P. lapponicus'' was originally collected from

Lapland Lapland may refer to: Places *Lapland or Sápmi, an ethno-cultural region stretching over northern Fennoscandia (parts of Norway, Sweden, Finland, and Russia) **Lapland (Finland) (''Lappi''/''Lappland''), a Finnish region *** Lapland (former pr ...

, a province in northern Sweden. The lichen has several unusual characteristics: it grows exclusively along with the rock moss ''

Andreaea ''Andreaea'' is a genus of rock mosses described by Johann Hedwig in 1801. They are small, delicate acrocarpous mosses (meaning that the capsules are formed at the tips of vertical branches) that form dark brown or reddish cushions on wet silic ...

'', it bears goniocyst-like parts (goniocysts are small aggregations of

photobiont A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.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 ...

e) and produces tiny

apothecia An ascocarp, or ascoma (), 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. Ascocarps are mo ...

that stand in the leaf axils of the moss, and it has thick

asci ASCI or Asci may refer to: * Advertising Standards Council of India * Asci, the plural of ascus, in fungal anatomy * Accelerated Strategic Computing Initiative * American Society for Clinical Investigation * Argus Sour Crude Index * Association of ...

. Poelt and Hertel thought the species occupied a basal position in the order

Lecanorales The Lecanorales are an order of mostly lichen-forming fungi belonging to the class Lecanoromycetes in the division Ascomycota. The order contains 26 families, 269 genera, and 5695 species. Families * Aphanopsidaceae * Biatorellaceae * Brigan ...

, and Poelt tentatively placed it in its own family, Pachyascaceae in a 1974 publication. This family was formally published in 2001. In 2020, it was classed within the

Lecanoromycetidae The Lecanoromycetidae are a subclass of fungi in the class Lecanoromycetes. This subclass contains five orders: the Caliciales , the Lecanorales , the Lecideales , the Leprocaulales , the Peltigerales , the Rhizocarpales , and the Teloschistales ...

but within uncertain order placement. Another lichen, which bears a superficial resemblance in the ascomata, was once placed in ''Pachyascus'' as ''P. byssaceus'' ; it is now known as '' Vezdaea aestivalis''.

References

Lecanorales Lichen genera Monotypic Lecanorales genera Taxa described in 1968 Taxa named by Hannes Hertel Taxa named by Josef Poelt {{Lecanorales-stub