Lecidea silacea (images of British lichens)

Thallus yellow-brown to rust-brown, deeply cracked into small, convex areoles; apothecia black, convex at maturity, arising between the areoles. Very local, on upland metalliferous rocks in the north and west.

Refs: Smith et al. (2009), 518; Purvis et al. (1992), 335; Moberg & Holmåson (1984), 124 (photo); Wirth (1995), 1: 510, 511 (photo); Hansen & Andersen (1995) 100 (photo); Thomson (1997), 377-9 (photo).

Lecidea is, obviously, 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