''Roccellographa'' 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 Roccellographaceae. These lichens form thin, tightly adhering crusts on rocks that reveal a bright orange colour when scraped, due to their

alga Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular microalgae, suc ...

l partner. The genus was established in 1902 by the Austrian lichenologist Julius Steiner and comprises four species that produce distinctive elongated, slit-like

fruiting bodies The sporocarp (also known as fruiting body, fruit body or fruitbody) of fungi is a multicellular structure on which spore-producing structures, such as basidia or asci, are borne. The fruitbody is part of the sexual phase of a fungal life cyc ...

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 the Austrian lichenologist Julius Steiner in 1902, with '' Roccellographa cretacea'' assigned as the

type Type may refer to: Science and technology Computing * Typing, producing text via a keyboard, typewriter, etc. * Data type, collection of values used for computations. * File type * TYPE (DOS command), a command to display contents of a file. * ...

, and at that time, the only species. Steiner established ''Roccellographa'' to accommodate lichens that resembled members of the

crustose lichen Crustose lichens are lichens that form a crust which strongly adheres to the Substrate (biology), substrate (soil, rock, tree bark, etc.), making separation from the substrate impossible without destruction. The basic structure of crustose lichen ...

family

Roccellaceae The Roccellaceae are a family (biology), family of mostly lichen-forming fungi in the order Arthoniales, established by the French botanist François Fulgis Chevallier in 1826. Species in the family exhibit various lichen growth forms, growth ...

but differed significantly in their reproductive structures. He noted that whilst the new genus belonged to 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 ...

based on its distinctive elongated, slit-like

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 ...

(), it formed a connecting link between the Roccellaceae and Graphidaceae families. 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 ...

, ''R. cretacea'', was characterised by its chalky white, -fruticose

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 formed dense, granular patches, and its distinctive

(fruiting bodies) that appeared either colourless or sparsely branched, with the barely exceeding the level of the surrounding thallus tissue. Three additional species have since been transferred to the genus from other genera.

Description

''Roccellographa'' lichens form a thin, even crust that adheres tightly to the rock. The surrounding —an outer weft of purely fungal strands—often develops into a dark, mosaic-like network that delineates neighbouring colonies. If the surface is gently scraped it reveals a bright orange tint, a sign of the underlying algal partner ('' Trentepohlia'') whose

carotenoid Carotenoids () are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, archaea, and fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips, corn, tomatoes, cana ...

pigments colour the exposed cells. Chemical spot tests detect psoromic and conpsoromic acids,

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 that help distinguish the genus from superficially similar rock-dwelling lichen crusts. Sexual fruit bodies are minute, blackish dots immersed in the

and frequently aligned in short rows or clusters. They lack a , so the rim is formed solely by the , which is dark brown above and pales towards the base. Inside, the spore-bearing layer (

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 ...

) contains stout, interwoven , while the supporting remains colourless. 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 ...

releases 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 and belongs to the '' Opegrapha''-type pattern, meaning its wall splits in two during discharge. The spores are elongated—either spindle-shaped or narrowly club-like—with up to seven internal 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 ...

). As they mature they acquire a grey-brown shade and develop slightly swollen ends (a form described as ).

Asexual Asexual or Asexuals may refer to: *Asexual reproduction **Asexual reproduction in starfish *Asexuality, the lack of sexual attraction to anyone or lack of interest in or desire for sexual activity. **Gray asexuality, the spectrum between asexualit ...

propagules (

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 ...

) have not been observed in the genus.

Species

*'' Roccellographa circumscripta'' *'' Roccellographa cretacea'' *'' Roccellographa muriformis'' *'' Roccellographa sorediata''

References

{{Taxonbar , from1=Q7353705 , from2=Q7178067 , from3=Q105499414 Arthoniomycetes Lichen genera Arthoniomycetes genera Taxa described in 1902