Bacidiaceae Tephromela atra var. atra Growth type crustose Chemical results: Cortex K+ yellow, C-, KC+ yellow. Medulla UV+ ice-white. The apothecia are purplish in section. Common on coastal siliceous or slightly basic rocks and walls, also inland. T. atra var. torulosa is only found on trees, the apothecia <1mm Thick, warted-areolate, whitish or pale grey thallus with blackish prothallus. Round or irregular, sessile or immersed black apothecia, the discs flat or concave, their margins swollen, entire or flexose, 1-2.5mm diam. Hymenium is dark purple-brown, the upper parts pale purple-violet. Spores are simple, 10-15 x 6-8 µm. Similar: Lecanora gangaleoides. Thecium dark green, UV +/- pale orange

Tephromela atra
On ironstone. Brands Bay, Dorset. January 2013