# Diorygma fuscum

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Species of lichen

Diorygma fuscum Scientific classification Kingdom: Fungi Division: Ascomycota Class: Lecanoromycetes Order: Graphidales Family: Graphidaceae Genus: Diorygma Species: D. fuscum Binomial name Diorygma fuscum Jian Li bis & Z.F.Jia (2016)

***Diorygma fuscum*** is a species of [corticolous](/source/Corticolous_lichen) (bark-dwelling) [crustose lichen](/source/Crustose_lichen) in the family [Graphidaceae](/source/Graphidaceae).[1] It forms thin, pale grey crusts on bark surfaces and produces distinctive slit-like reproductive structures that are dusted with white powder ([pruina](/source/Glossary_of_lichen_terms#pruina)). The lichen reproduces through [ascospores](/source/Ascospore) that have a brick-like internal structure with multiple compartments, and it contains several [lichen substances](/source/Lichen_substance) that help distinguish it from related species. The species was first [scientifically described](/source/Species_description) in 2016 from specimens collected in [Fujian](/source/Fujian) Province. *Diorygma fuscum* is known only from low-elevation [primary forests](/source/Old-growth_forest) in China, where it grows alongside other bark-dwelling lichens.

## Taxonomy

*Diorygma fuscum* was [described](/source/Species_description) in 2016 by Jian Li and Ze-Feng Jia on the basis of material collected from bark in low-elevation forests at Wanmulin, [Fujian](/source/Fujian), China. The [epithet](/source/Botanical_name) *fuscum* refers to the brownish tone assumed by the mature, many-celled spores. [Morphologically](/source/Morphology_(biology)) the species falls squarely within *[Diorygma](/source/Diorygma)*—it has [lirellate](/source/Glossary_of_lichen_terms#lirellate), white-pruinose apothecia and *[Graphis](/source/Graphis_(lichen))*-type asci—but it differs from its closest ally *D. pruinosum* by having smaller spores (40–60 × 12–18 μm vs 95–170 × 19–50 μm), eight rather than one spore per ascus, and by containing stictic-series compounds instead of protocetraric acid. Chemical profiles likewise set it apart from *D. erythrellum* and *D. poitaei*, which share 8-spored asci but differ in their [secondary metabolite](/source/Secondary_metabolite) suites and degree of exciple [carbonisation](/source/Glossary_of_lichen_terms#carbonisation).[2]

## Description

The thallus forms a thin (60–100 μm), pale grey to olive-grey crust that adheres closely to bark. Its surface is uneven to faintly warty and lacks powdery or finger-like [propagules](/source/Propagule). A poorly developed [pseudocortex](/source/Glossary_of_lichen_terms#pseudocortex) only 5–10 μm thick overlies a 30–40 μm algal layer composed of green *[Trebouxia](/source/Trebouxia)*-type cells; below this, the [medulla](/source/Medulla_(lichenology)) is sparse. Apothecia are abundant, appearing as flexuous, often branched slits (lirellae) 1–4 mm long that begin immersed but later burst open and rise slightly above the thallus. Their discs are thickly dusted with a white powder ([pruina](/source/Glossary_of_lichen_terms#pruina)), and ageing fruit-bodies frequently crack along the disc surface. The lateral wall ([exciple](/source/Glossary_of_lichen_terms#exciple)) remains pale or only weakly brown and is largely uncarbonised except at the base. The spore-bearing [hymenium](/source/Hymenium), 100–180 μm tall, is [iodine](/source/Iodine)-positive (bluish violet), and its cap ([epithecium](/source/Glossary_of_lichen_terms#epithecium)) is well developed, consisting of tangled paraphysis tips rich in gelatinous walls. [Paraphyses](/source/Paraphyses) are 1–2 μm wide, repeatedly branch and re-join, and tend to stick together near the [ascus](/source/Ascus) tips. Each club-shaped ascus produces eight colourless to pale-brown, densely muriform [ascospores](/source/Ascospore) with 10–14 transverse and 3–4 longitudinal walls; a thin gelatinous [halo](/source/Glossary_of_lichen_terms#halo) surrounds each spore. No asexual [pycnidia](/source/Pycnidia) have been observed. Chemically, the lichen contains [stictic acid](/source/Stictic_acid) as a major metabolite together with minor or trace amounts of [constictic](/source/Constictic_acid), [hypostictic](/source/Hypostictic_acid), and [hypoconstictic acids](https://en.wikipedia.org/w/index.php?title=Hypoconstictic_acid&action=edit&redlink=1), and it shows no colour reactions in standard [spot tests](/source/Spot_test_(lichen)).[2]

## Habitat and distribution

*Diorygma fuscum* is known to occur only in [subtropical](/source/Subtropics) south-eastern China, where it inhabits the bark of trees in relatively dry, open pockets of lowland [primary forest](/source/Old-growth_forest) at 300–540 m elevation. Collections from Wanmulin ([Fujian](/source/Fujian) Province) indicate that it co-occurs with various other [script lichens](/source/Script_lichen) such as *[Graphis hossei](https://en.wikipedia.org/w/index.php?title=Graphis_hossei&action=edit&redlink=1)* and members of *[Lecanora](/source/Lecanora)* and the [Graphidaceae](/source/Graphidaceae), suggesting a preference for lightly shaded [trunks](/source/Trunk_(botany)) that experience regular air movement. Until further surveys are conducted in neighbouring provinces and countries, the authors suggest that the species should be regarded as a regional [endemic](/source/Endemism) of [subtropical](/source/Subtropical) East Asia.[2] *Diorygma fuscum* is one of ten species of *[Diorygma](/source/Diorygma)* known to occur in China.[3]

## References

1. **[^](#cite_ref-CoL_6D8SZ_1-0)** ["*Diorygma fuscum* Jian Li bis & Z.F. Jia"](https://www.catalogueoflife.org/data/taxon/6D8SZ). *[Catalogue of Life](/source/Catalogue_of_Life)*. [Species 2000](/source/Species_2000): Leiden, the Netherlands. Retrieved 17 June 2025.

1. ^ [***a***](#cite_ref-Li_&_Jia_2016_2-0) [***b***](#cite_ref-Li_&_Jia_2016_2-1) [***c***](#cite_ref-Li_&_Jia_2016_2-2) Li, Jian; Jia, Ze-Feng (2016). ["*Diorygma fuscum* sp. nov. from China"](https://doi.org/10.5248%2F131.717). *Mycotaxon*. **131** (3): 717–721. [doi](/source/Doi_(identifier)):[10.5248/131.717](https://doi.org/10.5248%2F131.717).

1. **[^](#cite_ref-Cui_et_al._2024_3-0)** Cui, Can; Li, Yujie; Xu, Jiahui; Zhao, Xin; Jia, Zefeng (2024). ["*Diorygma tiantaiense* sp. nov. and a checklist and key to *Diorygma* species from China"](https://doi.org/10.3390%2Fd16040213). *Diversity*. **16** (4): e213. [Bibcode](/source/Bibcode_(identifier)):[2024Diver..16..213C](https://ui.adsabs.harvard.edu/abs/2024Diver..16..213C). [doi](/source/Doi_(identifier)):[10.3390/d16040213](https://doi.org/10.3390%2Fd16040213).

Taxon identifiers Diorygma fuscum Wikidata: Q107638486 Wikispecies: Diorygma fuscum CoL: 6D8SZ GBIF: 10706982 IndexFungorum: 570263 MycoBank: 570263 SpeciesFungorum: 570263

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Adapted from the Wikipedia article [Diorygma fuscum](https://en.wikipedia.org/wiki/Diorygma_fuscum) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Diorygma_fuscum?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.