Hypotrachyna afrorevoluta (images of British lichens)

Thallus foliose, light grey, lobes smooth and often slightly lustrous above, to matt with surface very minutely rugulose, edges turned down and tinged tan-brown, soredia initially pustulate, marginal and laminal, with rather coarse, grey-green to dark grey soredia (green when wet), undersurface black, brown at margins, rhizines unbranched or some bifurcate, occasionally projecting horizontally as cilia from lobe margins; apothecia rare. Widespread and evidently frequent but under-recorded, on trunks and main branches of deciduous trees; only recently distinguished from H. revoluta.

Refs: Nordic Lichen Flora (2011) 4: 62, 157 (photo, printed too dark); Smith et al. (2009), 441 (briefly, under H. revoluta); Purvis et al. (1992), 430 (as Parmelia, briefly, under P. revoluta); Dobson (2011), 198 (photo); van Haluwyn et al. (2009), 96-7 (photo); Frahm et al. (2010), 110-11 (photo); Hinds & Hinds (2007), 277.

H. revoluta differs in its green soralia on the tips of terminal lobes, with finer soredia, and pale to darkish brown undersurface. Hinds & Hinds (2007) and Elix & Thell in Nordic Lichen Flora (2011) give useful descriptions of both species, and van Haluwyn et al. (2009) provide a valuable photographic comparison. Correct placement of some specimens is difficult, but they seem distinct when growing in proximity, H. afrorevoluta on trunks and main branches, H. revoluta favouring smaller branches.
I first encountered this species in 2009 (photographs above), at a time when the BLS website considered British records to be erroneous, but it was immediately apparent that this was not H. revoluta as I knew it and matched continental internet pictures of H. afrorevoluta. It is now generally accepted. Elix & Thell consider it more coastal than H. revoluta in Scandinavia.

lastdragon.org

Images of British Lichens