• Opegrapha mougeotii A.Massal.
Opegrapha mougeotii
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Where there are sheltered niches in the vertical, mortared walls of old monasteries, abbeys and castles, the beautiful gaping discs (lirellae: 0.6-1.5 x 0.3-0.5mm diam.) overflowing with grey-blue powdery pruina of this lichen, are most likely to be seen. The thin, scurfy thallus may act as a guide but it is the widely exposed, slit-like discs which draw the eye in through a hand lens. For confirmation under the microscope the spores are 4-7-septate, often with an enlarged middle cell. All reactions negative. Very local and scattered in Ireland.

Key characteristics

  • Lirellae, black, straight or curved at first becoming gaping (when fully expanded) revealing blue-grey or rarely green, powdery pruina
  • On sheltered, thickly mortared walls of old castles and churches, especially ruins.

Original text submitted by Vince J. Giavarini

 Simms, M. J., (2016). Opegrapha mougeotii A.Massal.. [In] LichenIreland. Accessed on 2018-07-23.