Arthoniaceae Diarthonis spadicea (Arthonia spadicea) Growth type crustose Thallus negative. Apothecia and pycnidia K+ pale purple Can be abundant near the base of shaded, basic-barked, deciduous trees in moist woodlands Immersed or greyish-green thallus with +/- rounded, flat or convex, black apothecia and frequent pycnidia. Spores 1-septate, 7-11 x 3-4 µm. Microscope photograph below. Similar: Arthonia didyma and Arthonia vinosa

Microscope photograph

Arthonia spadicea
Holton Lee and Puddletown, Dorset. December 2012, April 2017