''Pycnotrema'' is a small

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

of lichen-forming

fungi A fungus (plural, : fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified ...

in the family

Graphidaceae The Graphidaceae are a family of lichens in the order Ostropales. Distribution and ecology The vast majority of Graphidaceae species are restricted to the tropics. Most Graphidaceae species are epiphytic (i.e. they grow only on plants). Gene ...

. Its two species are characterised by their small, rounded

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 ...

l (fruiting body) pores.

Taxonomy

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 po ...

by Eimy Rivas Plata and

Robert Lücking Robert Lücking (born 1964) is a German lichenologist. He is a leading expert on foliicolous lichens–lichens that live on leaves. Life and career Born in Ulm in 1964, Lücking earned both his master's (1990) and PhD degree (1994) at the Univer ...

in 2012, with ''Pycnotrema pycnoporellum'' 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 authors indicate that there are no well-defined that separate the genus from ''

Ocellularia ''Ocellularia'' is a genus of lichens in the family Graphidaceae. The genus was circumscribed by Georg Friedrich Wilhelm Meyer in 1825. Species *'' Ocellularia africana'' *'' Ocellularia allosporoides'' *'' Ocellularia andamanica'' *''Ocellul ...

'' and ''

Myriotrema ''Myriotrema'' is a genus of lichen-forming fungi in the family Thelotremataceae. Species *'' Myriotrema aggregans'' *''Myriotrema arimense'' *'' Myriotrema barroense'' *'' Myriotrema calvescens'' *'' Myriotrema cinereoglaucescens'' *'' M ...

'' (in the broad sense), but

molecular A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...

analysis shows the

lineage Lineage may refer to: Science * Lineage (anthropology), a group that can demonstrate its common descent from an apical ancestor or a direct line of descent from an ancestor * Lineage (evolution), a temporal sequence of individuals, populatio ...

is distinct. This lichen was originally described by

William Nylander William Andrew Michael Junior Nylander Altelius (born 1 May 1996) is a Canadian-born Swedish professional ice hockey right winger for the Toronto Maple Leafs of the National Hockey League (NHL). Nylander was selected by the Maple Leafs in the ...

in 1876 as a species of ''

Thelotrema ''Thelotrema'' is a genus of lichenized fungi in the family Graphidaceae, the family to which all taxa in the former Thelotremataceae now belong. Members of the genus ''Thelotrema'' are commonly called barnacle lichens. Species , Species Fungo ...

''. A second species, '' P. fissurinum'', was added to the genus in 2015. It is found in Puerto Rico. The genus name is derived from the

epithet An epithet (, ), also byname, is a descriptive term (word or phrase) known for accompanying or occurring in place of a name and having entered common usage. It has various shades of meaning when applied to seemingly real or fictitious people, di ...

of the type species, ''pycnoporellum'', combined with the suffix ''-trema''. ''Pycnotrema'' is in the subfamily Fissurinoideae of the family

Description

''Pycnotrema'' is characterised by a

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 ...

that is light grey-green and varies from smooth to uneven in texture. It features a dense, cortex—a compact, tissue-like layer of fungal cells that protects the beneath, where the

photosynthesizing Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in c ...

algae reside. This layer, along with the

medulla Medulla or Medullary may refer to: Science * Medulla oblongata, a part of the brain stem * Renal medulla, a part of the kidney * Adrenal medulla, a part of the adrenal gland * Medulla of ovary, a stroma in the center of the ovary * Medulla of ...

—the innermost layer of the lichen—contains clusters of

calcium oxalate Calcium oxalate (in archaic terminology, oxalate of lime) is a calcium salt of oxalic acid with the chemical formula . It forms hydrates , where ''n'' varies from 1 to 3. Anhydrous and all hydrated forms are colorless or white. The monohydrate ...

crystals. The

(fruiting bodies) of ''Pycnotrema'' are typically immersed within the thallus and rounded, often aligning in lines across the surface. These structures feature a disc that is usually covered by a narrow, reddish-coloured pore and surrounded by an entire, brown-black margin. Unlike some other lichens, ''Pycnotrema'' does not develop a , which is a central support structure found in some fungal fruits. The wall surrounding the apothecial , known as the , is also prosoplectenchymatous and brown in colour, and lacks —filamentous structures that can protrude from the margins of some lichens. The

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 fe ...

(sterile filaments that fill the apothecium) are unbranched. The spores of ''Pycnotrema'' are produced eight per

ascus An ascus (; ) is the sexual spore-bearing cell produced in ascomycete fungi. Each ascus usually contains eight ascospores (or octad), produced by meiosis followed, in most species, by a mitotic cell division. However, asci in some genera o ...

(spore-bearing structure) and are —divided by multiple cross walls—

ellipsoid An ellipsoid is a surface that may be obtained from a sphere by deforming it by means of directional scalings, or more generally, of an affine transformation. An ellipsoid is a quadric surface; that is, a surface that may be defined as the ...

in shape, and feature thick walls that divide the internal space into rounded compartments. These spores are colourless and turn violet-blue when treated with

iodine Iodine is a chemical element with the Symbol (chemistry), symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , ...

, indicating the presence of

amyloid Amyloids are aggregates of proteins characterised by a fibrillar morphology of 7–13 nm in diameter, a beta sheet (β-sheet) secondary structure (known as cross-β) and ability to be stained by particular dyes, such as Congo red. In the hu ...

compounds. In terms of chemistry, ''Pycnotrema'' does not produce any

secondary metabolite Secondary metabolites, also called specialised metabolites, toxins, secondary products, or natural products, are organic compounds produced by any lifeform, e.g. bacteria, fungi, animals, or plants, which are not directly involved in the no ...

References

{{Taxonbar, from=Q22104324 Graphidaceae Graphidales genera Lichen genera Taxa described in 2012 Taxa named by Robert Lücking