Lecidella scabra (images of British lichens)

Thallus a pale- to dark-grey, cracked crust, initially with scattered greenish soralia but the whole thallus commonly becoming green-sorediate; apothecia small, black, concave to convex, when young with defined, more shiny, regular to convoluted margins. Widespread and often common on rocks, walls and stonework.

Refs: Smith et al. (2009), 523; Purvis et al. (1992), 339; Dobson (2005), 239 (photo); Dobson (2011), 244 (photo); van Herk & Aptroot (2004), 230-31 (photo); Valcárcel et al. (2003), 228-9 (photo).

Lecidella is part of the very large 'Lecidea group' of lichens – crustose species with dark or black apothecia that lack distinct 'thalline' margins, though they will usually have differentiated 'proper' margins the same colour as the disk. Microscopic examination of mature apothecia (and sadly they are often not mature) is usually necessary even to be sure of the genus, and field identification of all but a few distinctive species is risky. Dobson (2011), pp. 236-7, gives an invaluable analysis of the component genera.

lastdragon.org

Images of British Lichens