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Rhizocarpon petraeum (Wulfen) A. Massal

Synonyms:

Rhizocarpon concentricum auct.



Family: RHIZOCARPACEAE

Habitat: Ubiquitous

Description

    Thallus crustose, most often rounded, to 5 cm diam., or more, cracked and often slightly areolate towards the center, areoles angular, 0.5 mm across, crowded, white-chalk, whitish, pale grey, prothallus thin and narrow, dark grey. Apothecia up to 0.5 mm diam., sometimes arranged in concentric circles, innate, often angular or oval, disc flat becoming convex, rough, black, not pruinose, exciple persistent, paler and tinged with blue or green, sometimes white owing to pruine of the same colour. Ascii 8-spored, 120-140 x 30-50 µm according to our measures, Ascospores muriform, at first colourless, then  blackish, 20-50 x 13-25 µm according to literature, 22-37 x 12-20 µm according to our measures. Photobiont: Chlorococcoid. Medulla : K+ yellow, Pd+ orange. Not especially maritime, but not so rare on walls near the seashore when alkalised by the mortar, or on neutral rocks. Not to be confused with Rhizocarpon reductum of which the thallus usually is smaller and more cracked, less whitish or darker and with a conspicuous well-developed black prothallus, growing on siliceous rocks. See also some resembling Buellia species of which the ascospores are not muriform.







Rhizocarpon petraeum L'Aber en Crozon 4
Joël QUERELLOU



Rhizocarpon petraeum Spores Eau L'Aber en Crozon 9
Jacques HAINE



Rhizocarpon petraeum Aber en Crozon
Michel DAVID



Rhizocarpon petraeum Aber en Crozon 2
Alain GERAULT



Rhizocarpon petraeum Pont-Croix 3
Bernard BOUFFINIER



Rhizocarpon petraeum L'Aber en Crozon 5
Joël QUERELLOU



Rhizocarpon petraeum L'Aber en Crozon 6
Bernard BOUFFINIER



Rhizocarpon petraeum Pont-Croix 2
Bernard BOUFFINIER



Rhizocarpon petraeum Lostmarc'h 1
Michel DAVID



Rhizocarpon petraeum Lostmarc'h 2
Michel DAVID



Rhizocarpon petraeum Lostmarc'h 3
Michel DAVID



Rhizocarpon petraeum Asque Ardennes
Jacques HAINE



Rhizocarpon petraeum L'Aber en Crozon 7
Jacques HAINE



Rhizocarpon petraeum Vieilles spores Eau L'Aber en Crozon 10
Jacques HAINE



Rhizocarpon petraeum Spores Bleu coton L'Aber en Crozon 11
Jacques HAINE



Rhizocarpon petraeum Asque Bleu coton L'Aber en Crozon 13
Jacques HAINE



Rhizocarpon petraeum Pointe de Kerdra 1
Michel DAVID



Rhizocarpon petraeum Pont-Croix 1
Bernard BOUFFINIER



Rhizocarpon petraeum Pointe de Dinan 2
Bernard BOUFFINIER



Rhizocarpon petraeum Pont-Croix 4
Bernard BOUFFINIER



Rhizocarpon petraeum Pont-Croix 5
Bernard BOUFFINIER



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