Lecanographaceae Alyxoria culmigena (Opegrapha herbarum) Chemical reactions negative Found on acidic to basic, smooth, often shady bark, also sometimes on plant stems (especially brambles) and sandstone. Occasionally host to Laeviomyces opegraphae Thin or inconspicuous pale grey, brownish or olive-green thallus. Lirellae usually simple, less frequently branched, the discs becoming fully open, rarely pruinose. Pycnidia are very rare. Spores 3-septate, 18-25 x 5-7 µm with a thin perispore. Microscope photograph below. Similar: Non-pruinose forms of Opegrapha ochrocheila have smaller spores without a perispore, 3-septate

Microscope photograph

Opegrapha herbarum
Arne and Badbury Rings, Dorset. February 2014, January 2017