Order: Arthoniales       Family: Arthoniaceae Species: Bryostigma lapidicola (Arthonia muscigena) Growth type crustose. Photobiont chlorococcoid. Photos: On Weigela twig. Knockgorm, Co. Cork, SW Ireland. Identified by John Douglass Found as small patches of thin olive-grey or greyish-brown minutely granular thallus with tiny convex black apothecia. Spores 1-septate with upper cell shorter and broader than lower, 8-12(-14) x 2.5-4 µm. Microscope photograph below. Chemical results negative Usually found on Sambucus (Elder) twigs but also on Acer and Ulmus trunks

Microscope photograph

Bryostigma lapidicola (Arthonia muscigena) . May 2012