• Arthonia atlantica P.James
Arthonia atlantica
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(Map updated: 11 August 2009)

This species grows below dry siliceous underhangs and in sheltered recesses in walls near the coast. It has a pale grey, scurfy thallus which looks unimpressive at first sight. However, closer inspection shows the presence of numerous iced-over discs joined together in a continuous mosaic reminiscent of Enterographa. Spores are two- to four-septate with an enlarged upper cell. The thallus tests Pd+ pale yellow or red. In Ireland, it is a western oceanic species and is known from Counties Kerry, Cork, Galway and Mayo, especially the offshore islands.

Key characteristics

  • Small, white to pale grey mosaic-forming crust with hidden Enterographa-like frosted discs; spores with enlarged upper cell
  • On the sheltered underhangs and shaded recesses of cliffs and walls along western coasts; Peterjamesia circumscriptum scratches orange with a finger nail.

Original text submitted by Vince J. Giavarini

 Simms, M. J., (2016). Arthonia atlantica P.James. [In] LichenIreland. Accessed on 2019-06-17.