''Melarthonis'' is fungal

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 ...

in the family

Chrysotrichaceae Chrysotrichaceae is a family of lichenized fungi in the order Arthoniales. Member of this family have a widespread distribution, but are especially prevalent in tropical areas. "Chrysothrichaceae" and "Chrysothricaceae" are alternative spellings ...

. It is a

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...

genus, containing the single species ''Melarthonis piceae'', a rare

corticolous lichen A corticolous lichen is a lichen that grows on bark.Alan Silverside's Lichen Glossary (a-f), Alan Silverside/ref> This is contrasted with lignicolous lichen, which grows on wood that has had the bark stripped from it,Alan Silverside's Lichen Glo ...

. This lichen forms a very thin, almost invisible layer of tiny pale-green granules on tree bark, along with small black reproductive structures. It is known only from a single location in

Hokkaido is the list of islands of Japan by area, second-largest island of Japan and comprises the largest and northernmost prefectures of Japan, prefecture, making up its own list of regions of Japan, region. The Tsugaru Strait separates Hokkaidō fr ...

, Japan, where it was discovered growing on

spruce A spruce is a tree of the genus ''Picea'' ( ), a genus of about 40 species of coniferous evergreen trees in the family Pinaceae, found in the northern temperate and boreal ecosystem, boreal (taiga) regions of the Northern hemisphere. ''Picea'' ...

trees in an

old-growth forest An old-growth forest or primary forest is a forest that has developed over a long period of time without disturbance. Due to this, old-growth forests exhibit unique ecological features. The Food and Agriculture Organization of the United Natio ...

Taxonomy

Both the genus and species were described as new to science in 2014 by Andreas Frisch and Göran Thor. The

type specimen In biology, a type is a particular wikt:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to ancho ...

was collected from

Mount Oakan is a stratovolcano located in Akan National Park in Hokkaidō, Japan. Geography and geology Mount Oakan sits in the Akan caldera northeast of Lake Akan. The volcano rises some above the surrounding terrain. The top of the volcano is above se ...

( Kushiro Province,

) at an altitude of ; there, it was found growing on the bark of a

tree in an

. It is only known to occur in the type locality. The genus name alludes to the black

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 ...

that are similar to those in genus ''

Arthonia ''Arthonia'' is a genus of lichens in the family Arthoniaceae. It was circumscribed by Swedish botanist Erik Acharius in 1806. It is a genus of thin crustose lichen of widely varying forms, commonly called comma lichens.Field Guide to California ...

'', while the

species epithet Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In Taxonomy (biology), taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany) ...

refers to the genus of 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 * ...

tree (''Picea'').

Description

''Melarthonis'' forms a very inconspicuous lichen layer. The

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 ...

is sparse and made up of minute, glossy, pale-green only 0.02–0.05 mm across. It lacks a protective , so each granule is little more than a tangle of colourless fungal threads that wrap around clusters of the

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 ( ...

l partner (a photobiont with rounded cells 4–9

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 ...

wide). No dark line or

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 ...

crystals are present, and the 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 themselves are about 1 μm thick and dusted with tiny colourless crystals. The reproductive structures are tiny black warts (

) that sit flat on the bark, yet bulge strongly in the middle. Each ascoma is rounded, 0.1–0.3 mm in diameter, and has a finely warted surface; in cross-section it is 70–80 μm thick. A narrow dark-brown rim (the , 10–15 μm wide) surrounds a clear, jelly-like interior. The outer hyphal tips project slightly and are pigmented dark brown, giving the ascoma its colour, while the very top layer () is 3–8 μm tall. Inside, a hyaline (translucent and colourless)

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 ...

35–40 μm high contains slender, club-shaped asci of the ''

''-type (27–34 × 10–12 μm), each producing eight colourless, three-celled

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 taper at both ends (10.0–14.0 × 2.5–4.0 μm) and never show a pinched "waist" at the internal walls. No asexual

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 ...

have been observed. Standard chemical spot tests are negative on the thallus, but the gelatinous tissue within the ascomata turns a very pale greenish blue in iodine–potassium iodide (KI+) and shows no hemi-amyloid cap () inside the asci.

References

{{Taxonbar , from1=Q107279649 , from2=Q108041969 Arthoniomycetes Arthoniomycetes genera Lichen genera Taxa described in 2014 Monotypic Ascomycota genera Taxa named by Göran Thor Taxa named by Andreas Frisch