Verrucariaceae Thelidium pyrenophorum Growth type crustose. BLS conservation evaluation: LC NS Chemical results negative Can be found on limestone, mortar, mica-schist and base-rich siliceous rocks. Common on limestone gravestones. Immersed or superficial greyish or white thallus, the prominent perithecia without a thalline collar at the base. Ostiole inconspicuous or slightly depressed. Spores 0-1 septate, (16-)21-28(-36) x (8-)10-13(-16) µm. Micrograph below. Similar: T. papulare. Usually with thalline collar at base of perithecia

Microscope photograph

Thelidium pyrenophorum
Canford Magna, Dorset. February 2016