Caloplaca limitosa (Nyl.) H. Olivier

    Thallus crustose, cracked to areolate, pale grey, pale grey-ochre, pale grey-olive, dark grey-olive when old, prothallus always present, conspicuous, blackish tinged blue, sometimes visible between areoles. Apothecia usually numerous, 0.5-1.5 mm diam., disc flat to slightly convex, red, rusty when young, turning lead-grey to olive-brown when old. Ascii 8-spored. Ascospores polarilocular, colourless, (10) 12-13 (17) x (5) 6-7 (10) µm, septum thickness 4-7 mm. Pycnidia numerous, visible as minute red dots. Photobiont: Trebouxia. Thallus and apothecia: K+ purple. Coastal Mediterranean species, rare, thermophile, in the seawater spray zone on siliceous well lit rocks. N.B. Caloplaca crenularia lookalike but with a very important black hypothallus.