Arthoniaceae Arthonia didyma Growth type crustose. Photobiont Trentepohlia Red-brown pigment K+ grey or olive. Epithecium, hymenium and sometimes hypothecium with orange-red K+ purple-violet pigment Smooth bark of shrubs and trees (often Corylus) in unpolluted woodlands Thallus +/- inconspicuous, pale brownish or olive-grey. Small, flat, brown or black apothecia, irregular, rounded or shortly linear. Spores are 1-septate, 14-17 x 4.5-7 µm, colourless then becoming brownish and warted. Pycnidia are rare. Micrographs below. Arthonia spadicea has larger apothecia and smaller spores. A. muscigena (now Bryostigma lapidicola), photobiont chlorococcoid, narrower spores

Micrographs





Arthonia didyma
Brands Bay and Broadstone, Dorset. January 2013, March 2020, January 2024