Psoraceae Protoblastenia calva Growth type crustose Chemical results: Apothecia K+ crimson Only found on hard limestone. N.B. Many British records of P. calva are of Protoblastenia lilacina, apothecia K- or with only a very weak reaction The smooth, cracked, white or pale-grey thallus is +/- immersed with large (to 1.5mm), convex, deep-orange apothecia initially in shallow pits. Micrograph of apothecia showing K+ crimson reaction. Similar: Protoblastenia rupestris is common on mortar and calcareous rocks, comparison below.

Micrograph

Protoblastenia calva
Godlingston Hill, Studland and Wool, Dorset. October 2012, February 2014, March 2017