Rhizocarpon eupetraeum (Nyl.) Arnold

Flora, 53: 478, 1870. Basionym: Lecidea eupetraea Nyl. - Flora, 53: 36, 1870.
Synonyms: Lecidea parapetraea Nyl.; Lecidea petraeiza Nyl.; Rhizocarpon arcticum Räsänen; Rhizocarpon dissentiens Arnold; Rhizocarpon endamyleum Th. Fr.; Rhizocarpon grande f. eupetraeum (Nyl.) Th. Fr.; Rhizocarpon petraeizum (Nyl.) Kieff.
Distribution: N - Ven, TAA, Piem (Isocrono & al. 2004), VA (Piervittori & Isocrono 1999), Emil (Fariselli & al. 2020). C - Tosc, Marc, Mol (Nimis & Tretiach 1999). S - Pugl (Nimis & Tretiach 1999).
Description: Thallus crustose, episubstratic, whitish grey, grey to rarely pale brown, dull, areolate, forming 2-6 cm wide patches delimited by a dark prothallus, the areoles contiguous, 0.3-1(-1.4) mm wide, 0.4-0.8 mm thick, strongly convex, smooth. Medulla white, I+ faintly blue. Apothecia lecideine, black, 0.3-1(-1.3) mm across, with a soon convex disc and a thin, soon excluded proper margin. Epithecium brown to brown-black, K+ strongly purple-red, rarely K-; hymenium colourless, 100-140(-160) µm high; paraphysoids coherent, branched and anastomosing; hypothecium brown, K-. Asci 8-spored, clavate, fissitunicate, with a well-developed tholus that is K/I- in lower part and K/I+ blue near the apex, lacking an ocular chamber, Rhizocarpon-type. Ascospores muriform, many-celled, dark brown to brown-black, 19-40 x 10-18 µm. Pycnidia black, subglobose, developing on the prothallus or immersed in the areoles. Conidia hyaline, filiform, 8-14 x 0.5-1.4 µm. Photobiont chlorococcoid. Spot tests: medulla K+ yellow turning red (needle-like crystals), C-, KC-, P+ pale yellow. Chemistry: medulla with norstictic acid.
Note: on inclined to vertical faces of acidic siliceous rocks, mostly sandstone, with a wide altitudinal range, up to the nival belt in the Alps.
Growth form: Crustose
Substrata: rocks
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly sexual

Commonnes-rarity: (info)

Alpine belt: rare
Subalpine belt: very rare
Oromediterranean belt: extremely rare
Montane belt: extremely rare
Submediterranean belt: extremely rare
Padanian area: absent
Humid submediterranean belt: absent
Humid mediterranean belt: absent
Dry mediterranean belt: absent

pH of the substrata:

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Solar irradiation:

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Aridity:

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Eutrophication:

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Poleotolerance:

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Altitudinal distribution:

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Predictive model
Herbarium samples
INDEX FUNGORUM GBIF DOLICHENS

Leif Stridvall - Source: http://www.stridvall.se/la/galleries.php



P.L. Nimis CC BY-SA 04
TSB 24997


Pier Luigi Nimis - CC BY-SA 4.0
Herbarium: TSB 25997


Wolfgang von Brackel - CC BY-4.0
Germany, Bavaria, Plöckenstein


Photo by E. Timdal. Source: Möller E.J., Timdal E., Haugan R., Bendiksby M. 2025. Integrative taxonomy and genus delimitation in the Rhizocarpaceae (lichenized Ascomycota). Fungal Syst. Evol., 16: 215-231. – CC BY-NC-ND
R. eupetraeum, Greenland, O-L-139134.