Thallus thin, grey, containing crystal clusters that may be visible as translucent dots when moist (Edwards et al., in Smith et al., 2009), surface with scattered, small (1mm), convex, pale yellow soralia; apothecia rare, variable in colour, said to have margins that become turned under. Generally on smooth bark, in humid woodland in the west, rare elsewhere.
Refs: Smith et al. (2009), 490; Purvis et al. (1992), 308; Dobson (2005), 225-6 (photo); Dobson (2011), 229 (photo).