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Opegrapha

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Opegrapha
Opegrapha cesareensis
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Fungi
Division: Ascomycota
Class: Arthoniomycetes
Order: Arthoniales
Family: Opegraphaceae
Genus: Opegrapha
Ach. (1809)
Type species
Opegrapha vulgata
(Ach.) Ach. (1809)
Synonyms[1]
  • Hysterina (Ach.) Gray (1821)
  • Kalaallia Alstrup & D.Hawksw. (1990)
  • Leciographa A.Massal. (1854)
  • Lecoglyphis Clem. (1909)
  • Mycopegrapha Vain. (1921)
  • Opegrapha † Hysterina Ach. (1810)
  • Opegrapha subgen. Sclerographa Vain. (1890)
  • Opegraphella Müll.Arg. (1890)
  • Opegraphoidea Fink (1933)
  • Opegraphomyces E.A.Thomas ex Cif. & Tomas. (1953)
  • Phragmographum Henn. (1905)
  • Phyllographa (Müll.Arg.) Räsänen (1943)
  • Sclerographa (Vain.) Zahlbr. (1923)
  • Xylastra A.Massal. (1855)

Opegrapha is a genus of mostly lichen-forming fungi in the family Opegraphaceae. These lichens form crusty patches on bark, rock, or other lichens, and are easily recognized by their distinctive black, slit-like or rounded fruiting bodies that look like tiny scribbles or dashes on the surface. The genus includes more than 100 species found worldwide, with most partnering with orange-pigmented green algae, though some live as parasites on other lichens.

Description

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Opegrapha species form a crust-like thallus that adheres tightly to bark, rock or even the surface of other lichens. This crust may be paper-thin or rather thick and is often cracked into a mosaic of small areoles. Colours range from chalk white through shades of grey and mauve to dark brown or olive-green, and a narrow dark prothallus sometimes outlines individual colonies. Most members partner with the orange-pigmented green alga Trentepohlia, but a few live parasitically on lichens that employ different algal partners. Powdery reproductive patches (soralia) are uncommon and, when present, remain discrete rather than fusing into large swathes.[2]

The sexual fruit-bodies are characteristically lirellate apothecia—elongated, often branching slits that resemble tiny scribbles in the thallus. In bark-dwelling or lichenicolous forms these slits may round off into short dashes or nearly circular discs. Each apothecium sits flush with, or slightly above, the substrate; it lacks a true rim of thallus tissue, though a thin pseudo-margin may form. A tough black wall (excipulum) encloses the fertile layer and usually remains opaque, so the exposed surface looks like a narrow, glossy cleft; when thin sections are treated with the K spot test the internal tissues turn olive or reddish-brown, a useful field test. Inside, a gel-filled layer of branched, cross-walled filaments (paraphysoids) weaves among the club-shaped asci. These asci split apart along two walls when the eight ascospores are released—a mechanism called fissitunicate dehiscence—and a faint blue-staining ring at the tip can be seen with iodine staining. The spindle-shaped spores bear multiple cross-walls, start colourless and may develop a reddish-brown, grainy coat as they age. Minute black pycnidia, partially sunk in the crust, exude colourless curved conidia that provide an alternative means of dispersal. Despite the chemical diversity found in many roccellaceous lichens, Opegrapha generally lacks secondary lichen products.[2]

Taken together—crustose thallus, slit-like or rounded black apothecia with a pigmented excipulum, branched paraphysoids, multiseptate spores and fissitunicate asci—these traits distinguish Opegrapha from superficially similar genera such as Graphis (unbranched paraphyses and iodine-positive spores), Enterographa (much narrower, clustered apothecia) and Schismatomma (persistent thalline margin). Conidial size and shape are especially diagnostic at the species level, as is the number of spore septa. Ongoing molecular work shows that traditional morphological boundaries between Opegrapha and allied genera (e.g. Lecanactis, Lecanographa) need further refinement, but the suite of characters outlined above still provides a practical field definition of the genus.[2]

Species

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Opegrapha agelaeoides
Opegrapha niveoatra
Opegrapha intertexta

Species include:[3]

References

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  1. ^ "Synonymy. Current Name: Opegrapha Ach., K. Vetensk-Acad. Nya Handl. 30(2): 97 (1809)". Species Fungorum. Retrieved 24 September 2024.
  2. ^ a b c Cannon, P.; Coppins, B.; Ertz, D.; Fletcher, A.; Pentecost, A.; Simkin, J. (2021). Arthoniales: Opegraphaceae, including the genera Llimonaea, Opegrapha, Paralecanographa and Sparria (PDF). Revisions of British and Irish Lichens. Vol. 13. pp. 3–4.
  3. ^ Esslinger, T. L. "A Cumulative Checklist for the Lichen-Forming, Lichenicolous and Allied Fungi of the Continental United States and Canada, Version 22". Opuscula Philolichenum. 17: 6–268. Retrieved 19 January 2019.
  4. ^ Brodo, Irwin M.; Tønsberg, Tor (2019). "Opegrapha halophila (Opegraphaceae), a new lichen species from coastal British Columbia, Canada, and Alaska, U.S.A.". The Bryologist. 122 (3): 457–462. doi:10.1639/0007-2745-122.3.457.
  5. ^ a b Follmann, Gerhard; Werner, Birgit C. (2003). "Lichenicolous fungi occurring on Roccellaceae (Arthoniales) I. New species from South America". Journal of the Hattori Botanical Laboratory. 94: 261–292.
  6. ^ Aptroot, André; Cáceres, Marcela Eugenia da Silva (2017). "New Arthoniales from Amapá (Amazonian North Brazil) show unexpected relationships". The Lichenologist. 49 (6): 607–615. doi:10.1017/s0024282917000500.
  7. ^ Kondratyuk, S.Y.; Lőkös, L.; Farkas, E.; Oh, S.-O.; Hur, J.-S. (2015). "New and noteworthy lichen-forming and lichenicolous fungi 2". Acta Botanica Hungarica. 57 (1–2): 77–141. doi:10.1556/abot.57.2015.1-2.10.
  8. ^ Vondrák, Jan; Kocourková, Jana (2008). "New lichenicolous Opegrapha species on Caloplaca from Europe". The Lichenologist. 40 (3): 171–184. doi:10.1017/s0024282908007536.
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