Megasporaceae Circinaria calcarea (Aspicilia calcarea) Growth type: Crustose Chemical results: Negative Common on limestone walls and tombstones where it can form large patches to 40cm diameter but not found on cement or mortar. Smooth white to pale-grey thallus, usually areolate and often surrounded by zoned, cracked, grey prothallus. Black, lecanorine, apothecia have distinct but non-persistent margins. Ascus 4-8 spored, spores 18-30 x 14-27 µm. Sometimes host to Toninia episema and Opegrapha parasitica Similar: Aspicilia contorta. Common on limestone, mortar and cement

Aspicilia calcarea
On limestone wall. Westbourne, Dorset. November 2012