Incertae sedis Petractis clausa Growth type crustose Chemical reactions negative. Photobiont Scytonema (cyanobacteria) On +/- damp, partly shaded, highly calcareous rocks, loose limestone and chalk pebbles Endolithic whitish or yellowish-white thallus with immersed urceolate apothecia that leave pits in the rock when they decay. Discs pinkish to pale orange, spores mostly 3-septate with distinct perispore, (15-)17-23(-35) x 5-7 µm excluding perispore. Microscope photographs below. Similar: Petractis nodispora, photobiont Trentepohlia. Gyalecta jenensis, photobiont Trentepohlia, submuriform spores

Microscope photographs





Petractis clausa
Canford Magna and Ulwell Gap, Dorset. January 2016