Acarosporaceae Acarospora privigna (Polysporina simplex) Growth type crustose Chemical results negative Common on siliceous rocks, granite memorials and chippings, slate roofs and walls. Also found on weakly calcareous rocks and pebbles. Thallus inapparent on granite or thin and scurfy, pale grey or green-grey on sandstone. Apothecia are partly immersed or sessile, often following cracks in the substratum. Discs non-pruinose, black (becoming dark red when wet) with wide, crenullate margins giving a knotted appearance. Asci with 100+ spores, 3-5 x 1-1.5 µm. Microscope photograph below.

Microscope photograph

Polysporina simplex
Church Knowle and Wareham, Dorset. March 2014, December 2016