Xanthocarpia crenulatella (Caloplaca crenulatella) Growth type crustose Chemical results: Apothecia K+ red/purple Can be frequent on flat concrete and mortar including drain covers, untreated patios and disused runways. The greyish-yellow thallus is usually thin and rimose but can vary from almost absent to subsquamulose. Crowded apothecia, the yellow-orange discs with slightly paler margins. Spores 15-18 x 6.5-8.5 µm, the septum less than 1/8 spore length. Microscope photograph below. Similar: Caloplaca flavovirescens is larger, spores with wide septum

Microscope photograph

Caloplaca crenulatella
Wimborne Minster, Dorset. March 2017