Description: Formerly known by the name Polyblastia diminuta, this species is most likely to be found overgrowing the thallus of other lichens such as those belonging to the genera Polyblastia, Thelidium and Verrucaria on limestone. The thallus is immersed and the spherical discs (perithecia) form burrows or pits from which they project very slightly so they need to be dug out with the sharp edge of a razor blade. There are several lookalikes but under the microscope the rather small (22-28&

371;m long), brown, 6- to 15-celled, muriform spores and distinctive halo-like perispore are key features. Look for it on the carboniferous limestone; mainly western in Ireland.

Key Identification Features:

• It is lichenicolous = grows on other pit-forming limestone lichens forming smaller pits or burrows
• The small, brown, muriform spores surrounded by a perispore (like a transparent halo) help to distinguish it from similar species.

Original text submitted by Vince J. Giavarini

Distribution Map from NBN: Merismatium deminutum at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Merismatium deminutum at iNaturalist World Species Observations database.