[2][6] It has a yellow to dark olive green thallus with black perithecia which can become visible in older specimens,[7] giving rise to the British common name blackberries in custard.

However, in 2003, a paper by Javiar Etayo and André Aptroot proposed that this should be re-evaluated, with the European and Macaronesian specimens having the name Pyrenula hibernica.

[1] Pyrenula hibernica grows on the smooth bark of Corylus (hazel), Ilex (holly), and Sorbus trees in sheltered, moist ravines,[10] as well as more open slopes, especially in Ireland.

[12] Pyrenula hibernica is a vulnerable species in the IUCN Red List categories, based on criteria D2 (having "a very restricted area of occupancy ... or number of locations").

[3] It was initially recorded as sterile Pyrenula macrospora because all the characteristic perithecia 'fruit' were fully immersed in the thalli and not visible from the surface; this was corrected after a sample was taken, revealing the fruit.