Species: Tephromela atra var. atra
Photos: Coastal rocks; Co. Cork, tree trunk; Co. Limerick, Ireland.
Thick, warted-areolate, whitish or pale grey thallus with blackish prothallus. Black apothecia, round or irregular, sessile or immersed. Discs flat / concave, margins swollen, entire or flexose, 1-2.5mm diam. Hymenium dark purple-brown, upper parts pale purple-violet. Asci 8-spored, spores simple, 10-15 x 5-8 Ám. Micro photo below.
Cortex K+ yellow, C-, KC+ yellow. Medulla UV+ ice-white. Apothecia purplish in section.
Common on coasts and inland on siliceous or slightly basic rocks and walls, occasional on trees.
T. atra var. torulosa is rare, only found on trees, apothecia <1mm
Similar: Lecanora gangaleoides. Thecium dark greenish. UV +/- pale orange