Degelia plumbea (images of British lichens)

Thallus lead grey, paler when dry, marked above with longitudinal marks and striations and with lobes usually concentrically undulate-ridged, felted blue-black beneath and at the margins, lacking isidia, apothecia usually plentiful, red-brown, lacking thalline margins but with pale 'proper' margins. Mostly in the north and north-west, on mossy trunks and sometimes rocks.

Refs: Smith et al. (2009), 371; Purvis et al. (1992), 230; Dobson (2005), 161 (photo); Dobson (2011), 167-8 (photo); Wirth (1995), 1: 369 (photo), 370; Nordic Lichen Flora (2007) 3: 97, 177 (photo); Moberg & Holmåson (1984), 167 (photo, as Parmeliella plumbea); Holien & Tønsberg (2008), 106 (photo); Arup et al. (1997), 177 (photo); Puntillo (1996), plate 15 (photo); Hinds & Hinds (2007), 233 (photo); Lichen Atlas of the British Isles 4: 1029 (1999).

A taxon previously considered a variant of D. plumbea but recently restored to specific rank is D. cyanoloma. It differs in its larger size, apothecia darker brown to blackish, lobe-tips less divided and with more prominent, curved, transverse ridges on the lobes giving it a distinctly shell-like appearance (see Blom & Lindblom (2009), Lichenologist 42: 23-27). It has been widely collected in Norway and it is proving to be locally frequent in north-western Scotland and in Ireland. The photographs cited above all appear to represent true D. plumbea.
Another but smaller look-alike is Pannaria rubiginosa, which has the same blue-black, felted margins to the lobes, but with upper surfaces of lobes smooth and with apothecia that have distinct, crenulate, truly thalline margins.

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Images of British Lichens