Diorygma

''Diorygma'' is a genus of lichen-forming fungi in the family Graphidaceae. The genus was circumscribed by Franz Gerhard Eschweiler in 1824. Species of the genus are widely distributed in tropical and subtropical regions of the world. These lichens form paint-like crusts on bark and rock that range from chalky white to light green, with elongated, pencil-like slits containing their spores that may flex and branch across the surface. The genus was established in 1824 for tropical script lichens with large, many-celled spores, but molecular studies in the 2000s and 2010s expanded it significantly by transferring species from other genera and revealing new diversity.

Taxonomy

The name ''Diorygma'' was coined by Franz Gerhard Eschweiler in 1824 for a group of neotropical script lichens in the family Graphidaceae that have large, many-celled () spores and a thin, naked hymenium. Elias Fries accepted the genus in 1825—likening it to what is now '' Arthonia''—but made no additional combinations. Eschweiler himself broadened the concept in 1833 by adding several species that subsequent work has reassigned to ''Fissurina'' and '' Platythecium''. Towards the end of the nineteenth century, Johannes Müller Argoviensis erected the genus '' Graphina'' for -spored taxa, retaining a handful of ''Diorygma'' species within his sections ''Platygraphina'' and ''Platygrammina'', thereby narrowing the scope of Eschweiler's original taxon.

Interest in the group revived in the twentieth century. Dharani Dhar Awasthi and Mamta Joshi, while revising '' Helminthocarpon'' in 1979, recognised that these lirellate lichens formed a discrete lineage, but instead of resurrecting Eschweiler's name they introduced ''Cyclographina''. In a comprehensive monograph of 2002, Bettina Staiger restored ''Diorygma'' for this assemblage and, on the basis of its rather unusual tissue organisation, suggested that it might fall outside the core Graphidaceae. Subsequent molecular analyses have confirmed that ''Diorygma'' does indeed belong within that family and have expanded its limits to include species with either single-spored, muriform asci or with spores divided only by transverse walls.

Description

Species of ''Diorygma'' form a crustose (tightly adherent, paint-like) thallus that ranges in hue from chalky white or cream to light olive-grey or green. The surface is generally dull and may be uneven, slightly wrinkled, or minutely warted; fine cracks are common. Unlike many other script lichens, the thallus lacks special powdery propagules (soralia or isidia). A true outer "skin" () is poorly developed or absent, while the interior medulla is white and often riddled with conspicuous crystal deposits. The embedded partner alga is '' Trentepohlia'', a filamentous green alga that imparts a faint orange tinge when exposed.

The sexual fruit-bodies are —elongate, pencil-like slits that may flex and branch across the thallus. Their margins can be thick and swollen or remain almost flush with the surface, and the exposed is usually brown, sometimes dusted with a whitish or yellowish bloom (). Internally, the lateral wall () may be pale or blackened ("") and often shows fine striations produced by repeated regrowth events. The hymenium—the spore-producing layer—is clear and oil-free but stains bluish-violet in iodine at its upper and outer portions. At its roof lies a tangle of gelatinous, net-like paraphyses that carry nodular tips and brown or colourless . Club-shaped asci have the so-called "''Graphis''-type" apex with a thickened inner cap, and they bear one to eight colourless ascospores. These spores are oblong with rounded ends, occasionally spindle-shaped, and show transverse walls (sometimes with additional vertical walls to give a brick-like, pattern); they measure roughly 15–250 × 5–60 μm and may turn blue-violet in iodine.

Asexual reproduction is rare and takes place in tiny pycnidia embedded in wart-like swellings about 0.1 mm across. These structures release minute, sausage-shaped to rod-shaped conidia 3.5–6 × 1–1.5 μm. Chemically, most species contain compounds of the norstictic or stictic acid families, while others produce protocetraric-series substances—secondary metabolites that can aid in species identification through chemical spot tests and thin-layer chromatography.

Species

, Species Fungorum accepts 80 species of ''Diorygma''.

*'' Diorygma aeolum''
*'' Diorygma africanum''
*'' Diorygma agumbense'' – India
*'' Diorygma alagoense'' – Brazil
*'' Diorygma albocinerascens'' – India
*'' Diorygma albovirescens'' – India
*'' Diorygma angusticarpum'' – Thailand
*'' Diorygma antillarum''
*'' Diorygma archeri'' – Vietnam
*'' Diorygma australasicum''
*'' Diorygma basinigrum''
*'' Diorygma cameroonense'' – Africa
*'' Diorygma chumphonense'' – Thailand
*'' Diorygma circumfusum''
*'' Diorygma citri'' – Thailand
*'' Diorygma confluens''
*'' Diorygma conprotocetraricum'' – Thailand
*'' Diorygma dandeliense'' – India
*'' Diorygma dealbatum'' – India
*'' Diorygma defectoisidiatum'' – Brazil
*'' Diorygma epiglaucum''
*'' Diorygma erythrellum''
*'' Diorygma excipuloconvergentum'' – India
*'' Diorygma extensum''
*'' Diorygma fuscopruinosum'' – Thailand
*'' Diorygma fuscum'' – China
*'' Diorygma gyrosum'' – Brazil
*'' Diorygma hieroglyphicellum'' – Thailand
*'' Diorygma hieroglyphicum''
*'' Diorygma hololeucum''
*'' Diorygma inaequale'' – India
*'' Diorygma incantatum'' – Brazil
*'' Diorygma inexpectatum'' – Thailand
*'' Diorygma intermedium''
*'' Diorygma isabellinum''
*'' Diorygma isidiolichexanthonicum'' – Brazil
*'' Diorygma junghuhnii''
*'' Diorygma karnatakense'' – India
*'' Diorygma kurnoolense'' – India
*'' Diorygma lichexanthonicum'' – Brazil
*'' Diorygma longilirellatum'' – India
*'' Diorygma longisporum'' – Brazil
*'' Diorygma macgregorii''
*'' Diorygma manipurense'' – India
*'' Diorygma megaspermum'' – India
*'' Diorygma megasporum''
*'' Diorygma megistosporum'' – India
*'' Diorygma microsporum''
*'' Diorygma minisporum''
*'' Diorygma monophorum''
*'' Diorygma nigricans'' – Peru
*'' Diorygma norsubmuriforme'' – Brazil
*'' Diorygma occultum''
*'' Diorygma panchganiense'' – India
*'' Diorygma pauciseptatum'' – Brazil
*'' Diorygma poitaei''
*'' Diorygma pruinosum''
*'' Diorygma radiatum''
*'' Diorygma reniforme''
*'' Diorygma roseopruinatum'' – New Caledonia
*'' Diorygma rufopruinosum''
*'' Diorygma rufosporum'' – India
*'' Diorygma rupicola'' – India
*'' Diorygma salazinicum'' – Thailand
*'' Diorygma salvadoriense''
*'' Diorygma salxanthonicum'' – Brazil
*'' Diorygma saxicola'' – India
*'' Diorygma sipmanii''
*'' Diorygma soozanum''
*'' Diorygma sophianum'' – Brazil
*'' Diorygma spilotum''
*'' Diorygma sticticum''
*'' Diorygma streimannii'' – Australia
*'' Diorygma subalbatum'' – India
*'' Diorygma subpruinosum'' – Thailand
*'' Diorygma talisense''
*'' Diorygma thailandicum'' – Thailand
*'' Diorygma tibellii''
*'' Diorygma tocantinsense'' – Brazil
*'' Diorygma toensbergianum'' – Brazil
*'' Diorygma tuberculosum''
*'' Diorygma upretii''
*'' Diorygma verrucirimosum'' – India
*'' Diorygma wallamanensis'' – Australia
*'' Diorygma wilsonianum''

References

Cited literature

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{{Taxonbar, from=Q5279571

Graphidales genera
Lichen genera
Taxa named by Franz Gerhard Eschweiler
Taxa described in 1824