''Austrotrema'' 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 ...

lichen A lichen ( , ) is a hybrid colony (biology), colony of algae or cyanobacteria living symbiotically among hypha, filaments of multiple fungus species, along with yeasts and bacteria embedded in the cortex or "skin", in a mutualism (biology), m ...

-forming

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

in the family

Graphidaceae The Graphidaceae are a family of lichen-forming fungi in the order Graphidales. The family contains nearly a hundred genera and more than 2000 species. Although the family has a cosmopolitan distribution, most Graphidaceae species occur in tropic ...

. It is primarily found in the Australian-Southeast Asian region. The genus is characterized by small, pore-like with a double margin, faintly amyloid ascospores, and

stictic acid Stictic acid is an aromatic organic compound, a product of secondary metabolism in some species of lichens. Stictic acid is the subject of preliminary biomedical research. Stictic acid has cytotoxic and apoptotic effects ''in vitro ''In v ...

chemistry. ''Austrotrema'' species grow on tree bark and have a continuous

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 ...

with a that is –featuring densely packed, filamentous fungal

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 o ...

e that run parallel to the surface of the lichen, creating a compact and firm texture. The genus is closely related to ''

Thelotrema ''Thelotrema'' is a genus of lichen-forming 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. Description ''Thelo ...

'' and '' Leucodecton'', but can be distinguished from them based on

molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

data, specific morphological traits, and its secondary chemistry. Currently, ''Austrotrema'' comprises three species.

Taxonomy

''Austrotrema'' 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 ...

by lichenologists Ian Medeiros,

Robert Lücking Robert Lücking (born 1964) is a German lichenologist, known for his extensive research on foliicolous lichens (lichens that live on leaves) and his significant contributions to the taxonomy, ecology, and biodiversity of fungi and lichens. He e ...

, and H. Thorsten Lumbsch in 2017. The genus was created to accommodate the three species of the ''Thelotrema bicinctulum''

species complex In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...

, which molecular phylogenetic analysis showed to be sufficiently genetically distinct to warrant placement in a new genus. ''Austrotrema'' is characterized by its small, pore-like with a double margin, faintly

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

ascospores, and

chemistry. 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 ...

for this genus is ''Austrotrema bicinctulum'', originally described as ''Thelotrema bicinctulum'' by

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

in 1861. The genus name ''Austrotrema'' is derived from the distribution of the type species in the Australian-Southeast Asian region.

Description

''Austrotrema'' lichens grow on the bark of trees and have a continuous thallus (body) with no

prothallus A prothallus, or prothallium, (from Latin ''pro'' = forwards and Greek ''θαλλος'' (''thallos'') = twig) is usually the gametophyte stage in the life of a fern or other pteridophyte. Occasionally the term is also used to describe the young ...

. The of these lichens is , featuring an irregular to thick layer of photobiont '' Trenepohlia'' green algal cells, interspersed with

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

crystal clusters. The medulla is indistinct and located between the upper and lower layers of the . The minute are round and can be either immersed or barely . The is almost entirely covered by a narrow pore, with a light to dark grey colour and a white- appearance. The is distinct and may be slightly to deeply fissured, surrounded by a pale rim formed by the double margin. The is thin, smooth, and ranges from yellow to olive-brown, with entire to slightly eroded or fissured edges. The is and separated from the covering thalline layer by a split. A is absent, while the is prosoplectenchymatous and

hyaline A hyaline substance is one with a glassy appearance. The word is derived from , and . Histopathology Hyaline cartilage is named after its glassy appearance on fresh gross pathology. On light microscopy of H&E stained slides, the extracellula ...

. 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 ...

is hyaline and clear, while the is gray and granular. The unbranched have smooth tips, and are present to indistinct. The asci are

fusiform Fusiform (from Latin ''fusus'' ‘spindle’) means having a spindle (textiles), spindle-like shape that is wide in the middle and tapers at both ends. It is similar to the lemon (geometry), lemon-shape, but often implies a focal broadening of a ...

, with eight per ascus. The ascospores are hyaline,

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 ...

, tapering at one end, and transversely

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

to somewhat with lens-shaped . have not been observed to occur in this genus. The secondary chemistry of ''Austrotrema'' lichens includes stictic acid as the major component, along with various related substances in minor or trace amounts.

Comparison with related genera

''Austrotrema'' bears resemblance to certain species of ''

'', and its distinction from ''Thelotrema'' at the genus level can only be made with

data. However, ''Austrotrema'' differs from similar ''Thelotrema'' species with transversely septate or small muriform ascospores and stictic acid due to its dense, prosoplectenchymatous cortex. ''Austrotrema'' can also be confused with '' Leucodecton'' species, but its close relationship with '' Nadvornikia hawaiiensis'' places it in the same

tribe The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide use of the term in English is in the discipline of anthropology. The definition is contested, in part due to conflict ...

as ''Austrotrema''. Within the Wirthiotremateae tribe, ''Austrotrema'' can be distinguished from ''

Asteristion ''Asteristion'' is a genus of lichen-forming fungi in the family Graphidaceae. It has seven species. Previously considered a synonym (taxonomy), synonym of either ''Phaeotrema'' or ''Thelotrema'', molecular phylogenetics, molecular evidence led ...

'' by its small ascomata with entire, pore-like thalline margin, and from ''Wirthiotrema'' by its less glossy thallus that does not split internally. The thalli of ''Wirthiotrema'' species tend to be more greenish, while those of ''Austrotrema'' are brownish.

Species

* '' Austrotrema bicinctulum'' – Australasia * '' Austrotrema myriocarpum'' – South America * '' Austrotrema terebrans'' – Cameroon; India; Thailand

References

{{Taxonbar, from=Q101614612 Graphidaceae Graphidales genera Lichen genera Taxa described in 2017 Taxa named by Robert Lücking Taxa named by Helge Thorsten Lumbsch