Phaeophyscia endophoenicea (images of British lichens)

Similar to P. orbicularis and showing the same colour range, but thallus with a less regular outline, soralia initially marginal and lip-shaped, lower medulla yellow to orange (purple with KOH), upper medulla white; apothecia rare. Widespread but very scarce or overlooked on somewhat shaded trunks in old parkland and forest.

Refs: Smith et al. (2009), 694; Purvis et al. (1992), 464; Dobson (2005), 333; Dobson (2011), 335; Nordic Lichen Flora (2002) 2: 29, 96 (photo); Arup et al. (1997), 229 (photo); Thor & Arvidsson (1999), 304 (photo), 415; Wirth (1995), 2: 717 (photo), 730; Frahm et al. (2010), 130 (photo); Lichen Atlas of the British Isles 3: 1105 (1998).

Sorry, it's a pretty rubbish photograph, taken quickly on the end of the accursed wobbly monopod while in a queue of people all wanting to photograph the same thing. I would have rejected it, but it is not illustrated in Dobson and it does show that the young soralia are marginal and lip-shaped and that the lower medulla is orange where the thallus is broken.

lastdragon.org

Images of British Lichens