Xanthoparmelia mougeotii (images of British lichens)

Thallus foliose, green-grey or distinctly yellow-grey (but commonly appearing pure grey in digital photographs or with digital printing technology), lobes radiating, usually narrow and somewhat serpentine, often convex in cross-section or flattened at the tips, cracked and brown in the centre part of the thallus, with subglobose yellow to grey-yellow soralia on the lobe surfaces, lower surface black; apothecia small, with brown discs and pale, crenulate margins, said to be rare. Widespread and locally common on exposed, base-poor rocks and gravestones, able to colonise various man-made surfaces.

Refs: Smith et al. (2009), 965; Purvis et al. (1992), 429 (as Parmelia); Dobson (2005), 460 (photo); Dobson (2011), 469 (photo); Jahns (1983), 194-5 (photo, as Parmelia); Fox, Guest & Harmer (2003), plate 6 (photo); van Herk & Aptroot (2004), 294-5 (photo); Nordic Lichen Flora (2011) 4: 134, 173 (photo); Wirth (1995), 2: 644, 668 (photo, as Parmelia); Lichen Atlas of the British Isles 1: 1005 (1995) (as Parmelia).

Arctoparmelia incurva (page pending) could be confused with this species but has more crowded, uniformly convex lobes, turning under at the tips.

lastdragon.org

Images of British Lichens