Arthoniaceae Arthonia meridionalis Growth type crustose. Chemical results negative BLS conservation evaluation: VU D2 NR A Mediterranean and southern Atlantic species that has only been recorded in Britain from the Isle of Portland, Dorset. It occurs on limestone rocks and stones in sheltered, well-lit hollows below large boulders. Forms irregular, slightly raised patches of chalk-white thallus with numerous round or slightly elongated apothecia. The apothecia are black, thinly white pruinose and either immersed or level with the thallus. Asci 8-spored, spores colourless, 1-septate, 12-15 × 4.5-6 µm. Photobiont trentepohlioid. Similar: Diplotomma alboatrum has muriform spores

Arthonia meridionalis
On limestone, Portland, Dorset. February 2016