''Muellerella pygmaea'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of lichenicolous fungus in the family

Verrucariaceae The Verrucariaceae are a family of mostly lichenised fungi in the order Verrucariales. The lichen-forming species, which comprise the vast majority of the family, have a wide variety of thallus forms, and include crustose (crust-like), foliose ( ...

. It has a

cosmopolitan distribution In biogeography, cosmopolitan distribution is the term for the range of a taxon that extends across all or most of the world in appropriate habitats. Such a taxon, usually a species, is said to exhibit cosmopolitanism or cosmopolitism. The ext ...

in Arctic-alpine areas and grows on 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 ...

and apothecia of a number of hosts. Host species for ''Muellerella pygmaea'' include: * ''

Acarospora ''Acarospora'' is a genus of mostly lichen-forming fungi in the family Acarosporaceae. Most species in the genus are crustose lichens that grow on rocks in open and arid places all over the world. They may look like a cobblestone road or cracked ...

'' sp. * '' Acarospora smaragdula'' * '' Aspicilia calcarea'' * ''

Candelariella aurella ''Candelariella aurella'', the hidden goldspeck lichen or eggyolk lichen, is a yellow crustose lichen in the family Candelariaceae. It is commonly found on calcareous rock or wood or bark exposed to sunlight and which may have calcareous dust in ...

'' * '' Carbonea assentiens'' * ''

Lecanora alpigena ''Lecanora'' is a genus of lichen commonly called rim lichens.Field Guide to California Lichens, Stephen Sharnoff, Yale University Press, 2014, Lichens in the genus ''Squamarina'' are also called rim lichens. Members of the genus have roughly ci ...

'' * ''

Lecanora muralis ''Lecanora muralis'' ''(Protoparmeliopsis muralis)'' is a waxy looking, pale yellowish green crustose lichen, crustose lichen that usually grows in rosette (botany), rosettes radiating from a center (placoidiod, placodioid) filled with disc-like ...

'' * ''

Lecanora polytropa ''Lecanora polytropa'', commonly known as the granite-speck rim lichen, is a species of saxicolous lichen in the family Parmeliaceae. A small, inconspicuous species that grows in the cracks of rock surfaces, it has a cosmopolitan distribution an ...

'' * '' Lecidea grisella'' * '' Lecidea lapicida'' * '' Lecidea obluridata'' * '' Tephromela atra'' * '' Rhizocarpon geographicum'' * '' Rusavskia elegans''

References

Verrucariales Fungi described in 1855 Taxa named by Gustav Wilhelm Körber Fungi of Iceland {{Eurotiomycetes-stub