''Diplotomma'' 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 Caliciaceae. The genus has a widespread distribution and contains 14 species. These lichens form firmly attached, crust-like patches that range from pale to dark grey and can appear smooth or cracked into an irregular mosaic pattern on their

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (aquatic environment), the earthy material that exi ...

. They produce black, disc-shaped fruiting bodies that start buried in the crust and later emerge to sit roughly flush with the surface, often dusted with a greyish-white powder.

Taxonomy

The genus 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 Julius von Flotow in 1849. It was later wrapped into ''

Buellia ''Buellia'' is a genus of mostly lichen-forming fungi in the family Caliciaceae. The fungi are usually part of a crustose lichen. In this case, the lichen species is given the same name as the fungus. But members may also grow as parasites on lic ...

'' before being segregated from that genus by David Hawksworth in 1980.

Description

''Diplotomma'' species form a firmly attached, crust-like

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 ...

that sits on the

as a clearly delimited patch; in a few lichen-inhabiting ( lichenicolous) taxa the thallus may be very thin or partly immersed in the

host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County * Host Island, in the Wilhelm Archipelago, Antarctica People * ...

. The surface ranges from pale to dark grey and can appear smooth or cracked into an irregular mosaic. A dense outer is packed with minute crystals that remain intact when a fragment is placed in

potassium hydroxide Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash. Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which utili ...

solution (the K test). The algal partner () is a single-celled

green alga The green algae (: green alga) are a group of chlorophyll-containing autotrophic eukaryotes consisting of the phylum Prasinodermophyta and its unnamed sister group that contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ( ...

of the type, which provides

photosynthetic Photosynthesis ( ) is a Biological system, system of biological processes by which Photoautotrophism, photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical ener ...

energy. The sexual 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 ...

) start out buried in the thallus and later emerge so that the black sits roughly flush with the surface; a narrow, pale, scalloped rim of thallus tissue may encircle the disc in some species. The disc itself is often dusted with a greyish-white powder (). Microscopic examination shows only a rudimentary , merging seamlessly with the underlying , both of which are brown to nearly black. Thread-like

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 in the clear (I+ blue)

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 ...

; their tips swell and darken, giving the layer a tufted look. Each sac-like

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 ...

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 that are divided by cross-walls into two or more cells (sometimes almost forming a brick pattern, ) and have thick internal partitions (); mature spores are mid- to dark brown with rounded internal chambers ().

Vegetative reproduction Vegetative reproduction (also known as vegetative propagation, vegetative multiplication or cloning) is a form of asexual reproduction occurring in plants in which a new plant grows from a fragment or cutting of the parent plant or specializ ...

occurs in sunken, flask-shaped

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 appear as tiny brown dots; these release colourless, oval

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 ...

capable of starting new thalli. Chemically the genus is characterised by aromatic

depside A depside is a type of polyphenolic compound composed of two or more monocyclic aromatic units linked by an ester group. Depsides are most often found in lichens, but have also been isolated from higher plants, including species of the Ericaceae, ...

s, compounds that help separate its species from superficially similar grey crustose lichens.

Selected 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 ...

) accepts 14 species of ''Diplotomma'': * '' Diplotomma alboatrum'' * '' Diplotomma cedricola'' * '' Diplotomma chlorophaeum'' * '' Diplotomma epipolium'' * '' Diplotomma glaucoatrum'' * '' Diplotomma hedinii'' * '' Diplotomma murorum'' * '' Diplotomma niveum'' * '' Diplotomma parasiticum'' * '' Diplotomma pharcidium'' * '' Diplotomma porphyricum'' * '' Diplotomma rivas-martinezii'' * '' Diplotomma venustum'' * '' Diplotomma vezdanum''

References

{{Taxonbar, from=Q5280002 Caliciales Lichen genera Caliciales genera Taxa described in 1849 Taxa named by Julius von Flotow