''Arctomia'' is a genus of

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 Arctomiaceae. The genus was originally

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 ...

Theodor Magnus Fries Theodor "Thore" Magnus Fries (28 October 1832 – 29 March 1913), was a Sweden, Swedish botanist, lichenologist, and Arctic explorer. The son of the renowned mycologist Elias Magnus Fries, he served as a professor of botany and applied economic ...

in 1861. ''Arctomia'' has a

circumpolar distribution A circumpolar distribution is any range (biology), range of a taxon that occurs over a wide range of longitudes but only at high latitudes; such a range therefore extends all the way around either the North Pole or the South Pole. Taxa that are al ...

Description

''Arctomia'' grows as a thin crust that can look either or like a miniature patchwork of tiny leaf-like scales. When dry the surface is reddish-brown to nearly black and, unlike some gelatinous lichens, it does not swell appreciably after rain. The edge of a colony is indefinite and may develop small , but the whole

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 ...

remains low-lying. A single-cell-thick —essentially a skin of brown fungal cells—covers the surface, and the lichen never produces the powdery outgrowths (

isidia An isidium (plural: isidia) is a tiny, wart- or finger-like outgrowth on the thallus surface of certain lichen species. It is one of two principal types of vegetative reproduction, vegetative reproductive structures in lichens, the other being ...

) or

soralia Soredia are common reproductive structures of lichens. Lichens reproduce asexually by employing simple fragmentation and production of soredia and isidia. Soredia are powdery propagules composed of fungal hyphae wrapped around cyanobacteria or g ...

seen in many other genera. Sandwiched between the fungal threads are clusters of

cyanobacteria Cyanobacteria ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their bluish green (cyan) color, which forms the basis of cyanobacteri ...

of the genus ''

Nostoc ''Nostoc'', also known as star jelly, troll's butter, spit of moon, fallen star, witch's butter (not to be confused with the fungi commonly known as witches' butter), and witch's jelly, is the most common genus of cyanobacteria found in a variety ...

''; its cells, about 5–7

micrometre The micrometre (English in the Commonwealth of Nations, Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a uni ...

s (μm) across, sit in a clear jelly that gives the thallus a slightly glossy, rubbery feel when moist.

Sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...

takes place in minute disc-shaped fruit bodies (

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 ...

) that originate as tiny bumps inside the lobes and become more or less stalkless on maturity. These are flat to gently domed and merge smoothly with the surrounding thallus rather than being ringed by a distinct margin. Inside, slender branched filaments (

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 ...

) stand among the spore sacs; their tips broaden slightly and carry a brown pigment. Each

ascus An ascus (; : asci) 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 gen ...

belongs to the '' Trapelia''-type: it shows a thickened apex (the ) that stays colourless in iodine

staining Staining is a technique used to enhance contrast in samples, generally at the Microscope, microscopic level. Stains and dyes are frequently used in histology (microscopic study of biological tissue (biology), tissues), in cytology (microscopic ...

, while the surrounding gelatinous sheath stains blue, and it usually contains eight

ascospore In fungi, an ascospore is the sexual spore formed inside an ascus—the sac-like cell that defines the division Ascomycota, the largest and most diverse Division (botany), division of fungi. After two parental cell nucleus, nuclei fuse, the ascu ...

s. The spores themselves are long, spindle-shaped and divided by many cross-walls (

septa SEPTA, the Southeastern Pennsylvania Transportation Authority, is a regional public transportation authority that operates bus, rapid transit, commuter rail, light rail, and electric trolleybus services for nearly four million people througho ...

)—features that help them survive dispersal.

Asexual reproduction Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the f ...

occurs in embedded

pycnidia A pycnidium (plural pycnidia) is an asexual fruiting body produced by mitosporic fungi, for instance in the order Sphaeropsidales ( Deuteromycota, Coelomycetes) or order Pleosporales (Ascomycota, Dothideomycetes). It is often spherical or inve ...

that release tiny, rod-shaped

conidia A conidium ( ; : conidia), sometimes termed an asexual chlamydospore or chlamydoconidium (: chlamydoconidia), is an asexual, non- motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also ...

, and standard chemical spot tests detect no

secondary metabolite Secondary metabolites, also called ''specialised metabolites'', ''secondary products'', or ''natural products'', are organic compounds produced by any lifeform, e.g. bacteria, archaea, fungi, animals, or plants, which are not directly involved ...

s in the thallus.

Species

Species Fungorum ''Index Fungorum'' is an international project to index all formal names (Binomial nomenclature, scientific names) in the fungus Kingdom (biology), kingdom. As of 2015, the project is based at the Royal Botanic Gardens, Kew, one of three partn ...

(in the

Catalogue of Life The Catalogue of Life (CoL) is an online database that provides an index of known species of animals, plants, fungi, and microorganisms. It was created in 2001 as a partnership between the global Species 2000 and the American Integrated Taxono ...

) accept four species of ''Arctomia'': *'' Arctomia delicatula'' *'' Arctomia papuanorum'' *'' Arctomia teretiuscula'' – China *'' Arctomia uviformis''

Molecular phylogenetics 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 ...

evidence revealed inappropriate classifications for two species once placed in this genus, ''A. insignis'' and ''A. borbonica'' ; they were formally transferred to the genus '' Gabura'' in 2020. ''Arctomia fascicularis'' was confirmed to belong to ''Gabura'', a generic placement originally proposed by

Per Magnus Jørgensen Per Magnus Jørgensen (born 1944) is a Norwegian botanist and lichenologist, and Professor Emeritus of systematic botany at the University of Bergen. He is known for his work on the lichen families Pannariaceae and Collemataceae. Jørgensen wa ...

in 2014.

References

{{Taxonbar , from1=Q4787625 , from2=Q25407175 Baeomycetales Baeomycetales genera Lichen genera Taxa named by Theodor Magnus Fries Taxa described in 1861