Saxicolous on siliceous rock together with Ephebe hispidula. The specimen has a pale to dark grey thallus with a violet tinge. Perithecia are partly immersed, solitary or confluent. Spores 34–38 × 3–4 µm, 7-septate, fusiform.  The somewhat similar P. curnowii and P. grandis differ, for example, in spore characters.  New to Greenland. Although sparsely occurring at its habitats (moist, siliceous rocks at the border of watercourses and lakes) P. guentheri has a wide distribution in both northern and southern areas ranging from subarctic Greenland and North America to Italy and Sardinia (Purvis & James 1992, Esslinger & Egan 1995).