Roccellaceae Gyrographa saxigena (Opegrapha saxigena) Growth type crustose Chemical results negative. BLS conservation evaluation: LC NS Sc IR On sheltered, deeply shaded siliceous rocks, especially in old woodlands. Occasional on smooth bark. Can be locally frequent in the SW and West. Mosaic-forming thin or partially cracked dark-chocolate to deep purplish brown thalli surrounded by a thin dark prothallus. Apothecia are often sparse, short, rarely branched, the disc a persistent slit. Spores 3-septate, (15-)16-20(-22) x 4-5(-6) µm. Soredia absent. Micrograph below. Similar: Gyrographa gyrocarpa is sorediate with gyrose apothecia

Microscope photograph

Opegrapha saxigena
On chert. Portland, Dorset. February 2016