Chroodiscus Graphideus
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''Chroodiscus'' 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 ...
of leaf-dwelling lichens 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 ...
. These lichens form thin, smooth crusts directly on living leaves and are characterized by distinctive star-shaped
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 ...
that split into triangular segments, with centres ranging from grey to bright scarlet-red depending on their chemical composition. The genus is found throughout
tropical The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...
regions worldwide, growing in the shaded
understory In forestry and ecology, understory (American English), or understorey (English in the Commonwealth of Nations, Commonwealth English), also known as underbrush or undergrowth, includes plant life growing beneath the Canopy (biology), forest ca ...
of
rainforest Rainforests are forests characterized by a closed and continuous tree Canopy (biology), canopy, moisture-dependent vegetation, the presence of epiphytes and lianas and the absence of wildfire. Rainforests can be generally classified as tropi ...
s from lowland areas to mountain
cloud forest A cloud forest, also called a water forest, primas forest, or tropical montane cloud forest, is a generally tropical or subtropical, evergreen, Montane forest, montane, Tropical and subtropical moist broadleaf forests, moist forest characteri ...
s, where they serve as sensitive
indicators Indicator may refer to: Biology * Environmental indicator of environmental health (pressures, conditions and responses) * Ecological indicator of ecosystem health (ecological processes) * Health indicator, which is used to describe the health ...
of undisturbed forest conditions.


Taxonomy

''Chroodiscus'' was first introduced by the Swiss lichenologist
Johannes Müller Argoviensis Johann Müller (9 May 1828 – 28 January 1896) was a Swiss botanist who was a specialist in lichens. He published under the name Johannes Müller Argoviensis to distinguish himself from other naturalists with similar names. Biography Müller ...
in 1883 as a
section Section, Sectioning, or Sectioned may refer to: Arts, entertainment and media * Section (music), a complete, but not independent, musical idea * Section (typography), a subdivision, especially of a chapter, in books and documents ** Section sig ...
of the genus ''
Ocellularia ''Ocellularia'' is a genus of lichens in the family Graphidaceae. The genus was circumscribed by Georg Friedrich Wilhelm Meyer Georg may refer to: * Georg (film), ''Georg'' (film), 1997 *Georg (musical), Estonian musical * Georg (given name) ...
''. In his original description, Müller characterized the section by its layer being phyllactideum (containing
green algae 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 ...
arranged in a specific pattern) and its
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 ...
(fruiting bodies) being pale or variously coloured. He described 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 ...
, ''
Ocellularia argillacea ''Ocellularia'' is a genus of lichens in the family Graphidaceae. The genus was circumscribed by Georg Friedrich Wilhelm Meyer Georg may refer to: * Georg (film), ''Georg'' (film), 1997 *Georg (musical), Estonian musical * Georg (given name) ...
'', as having a clay-coloured to pale or greenish-clay coloured
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 was very thin, smooth, and interrupted by small globular swellings. The apothecia were measured at 0.2 to 0.5 millimetres wide and described as having broad, prominent margins. In 1890 he promoted the section to generic status.


Description

''Chroodiscus'' forms a thin, smooth to slightly glossy crust (
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 grows directly on living leaves (foliicolous) and lacks a true . Its
ascomata An ascocarp, or ascoma (: ascomata), is the fruiting body (sporocarp (fungi), sporocarp) of an ascomycete phylum fungus. It consists of very tightly interwoven hyphae and millions of embedded ascus, asci, each of which typically contains four to ...
are strikingly : minute discs that split into several triangular lobules which then curl back to give a star-shaped outline; the exposed centre ranges from grey to scarlet-red, according to pigment chemistry. A pale, borders each disc, while the clear
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 lax, branched
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 ...
and no . The asci are ''
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 ...
''-type (thin-walled, iodine-negative) and usually release eight hyaline
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 transversely 3–7-septate, thin-walled and non-
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 ...
(about 12–30 × 4–7 
μm The micrometre (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 unit of length in the International System ...
). Many species synthesise orange-red
anthraquinone Anthraquinone, also called anthracenedione or dioxoanthracene, is an aromatic hydrocarbon, aromatic organic compound with formula . Several isomers exist but these terms usually refer to 9,10-anthraquinone (IUPAC: 9,10-dioxoanthracene) wherein th ...
s or
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 ...
-derivatives that tint the discs; others are chemically inert. Species differ mainly in disc colour, spore size and chemistry: for example, ''C. argillaceus'' has grey discs and stictic acid, whereas ''C. mirificus'' develops vivid red discs rich in anthraquinones. The combination of star-shaped discs, absence of periphysoids and thin-walled, non-amyloid spores separates ''Chroodiscus'' from superficially similar genera such as '' Chapsa'', '' Astrochapsa'' and '' Pseudochapsa'', whose discs lack the lobules or whose spores react differently with iodine.


Ecology

The genus is strictly
pantropical A pantropical ("all tropics") distribution is one which covers tropical regions of both the Eastern and Western hemispheres. Examples of species include caecilians, modern sirenians and the plant genera ''Acacia'' and ''Bacopa''. ''Neotropical' ...
: records span Central and South America, West and Central Africa, Madagascar, India, Southeast Asia and north-east Australia. All known species are obligately foliicolous, colonising the shaded, humid
understory In forestry and ecology, understory (American English), or understorey (English in the Commonwealth of Nations, Commonwealth English), also known as underbrush or undergrowth, includes plant life growing beneath the Canopy (biology), forest ca ...
of evergreen rainforests from lowland plains up to the montane
cloud forest A cloud forest, also called a water forest, primas forest, or tropical montane cloud forest, is a generally tropical or subtropical, evergreen, Montane forest, montane, Tropical and subtropical moist broadleaf forests, moist forest characteri ...
belt. A
phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology (physical form and structure), its developmental processes, its biochemical and physiological propert ...
-based
phylogeny A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or Taxon, taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, M ...
indicates a South American origin in the mid-
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
(roughly 120–100 Ma) followed by stepwise dispersal through Africa, India and Southeast Asia, with most present-day taxa now restricted to a single continent. Because they depend on intact, moist canopy
microclimate A microclimate (or micro-climate) is a local set of atmosphere of Earth, atmospheric conditions that differ from those in the surrounding areas, often slightly but sometimes substantially. The term may refer to areas as small as a few square m ...
s, ''Chroodiscus'' species are considered sensitive
indicators Indicator may refer to: Biology * Environmental indicator of environmental health (pressures, conditions and responses) * Ecological indicator of ecosystem health (ecological processes) * Health indicator, which is used to describe the health ...
of undisturbed tropical forest and tend to disappear after forest clearance or prolonged drought.


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 19 species of ''Chroodiscus'': *'' Chroodiscus africanus'' *''
Chroodiscus anomalus ''Chroodiscus'' is a genus of leaf-dwelling lichens in the family Graphidaceae. These lichens form thin, smooth crusts directly on living leaves and are characterized by distinctive star-shaped fruiting bodies that split into triangular segme ...
'' *'' Chroodiscus argillaceus'' *'' Chroodiscus australiensis'' *'' Chroodiscus australis'' *'' Chroodiscus coccineus'' *'' Chroodiscus defectus'' *'' Chroodiscus graphideus'' *'' Chroodiscus homchantarae'' *'' Chroodiscus khaolungensis'' *'' Chroodiscus khaosokensis'' *'' Chroodiscus mirificus'' *'' Chroodiscus neotropicus'' *'' Chroodiscus parvisporus'' *'' Chroodiscus subhimalayanus'' – India *'' Chroodiscus submuralis'' *'' Chroodiscus verrucosus''


References

{{Taxonbar, from=Q5114276 Graphidaceae Taxa described in 1883 Graphidales genera Taxa named by Johannes Müller Argoviensis Lichen genera