Arthoniaceae Arthonia didyma Growth type crustose. Photobiont Trentepohlia Red-brown pigment K+ grey or olive. Epithecium yellow-brown to red-brown, K +/- purple-violet. Hymenium colourless to spotty pale orange-brown, pigmented parts K+ purple-violet or K- Smooth bark of shrubs and trees (often Corylus) in unpolluted woodlands Thallus +/- inconspicuous, pale brownish or olive-grey. Small, flat, brown or black apothecia are irregular, rounded or shortly linear. Spores 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