Physconia grisea (images of British lichens)

Foliose, thallus green when wet, drying grey or brown-grey, but densely white-pustulate pruinose over the whole surface, medulla white, margins coarsely sorediate, undersides with long rhizines, which are single to tufted and usually fused at the base but then the majority unbranched, pale or becoming blackish; apothecia uncommon, with pruinose, grey-blue disks and sorediate margins. Widespread and often common, but much less frequent in the north and west, on stonework, or tree bark, especially when the latter (according to books) is dust-impregnated.

Refs: Smith et al. (2009), 705; Purvis et al. (1992), 472; Dobson (2005), 343-4 (photo); Dobson (2011), 344 (photo); Jahns (1983), 252-253 (photo, printed with incorrect colour in my copy); Whelan (2011), 132 (photo); Nordic Lichen Flora (2002) 2: 40, 100 (photo); van Haluwyn et al. (2009), 94-5 (photos); van Herk & Aptroot (2004), 304-5 (photo); Wirth (1995), 2: 729, 738 (photo); Wirth et al. (2004), 125 (photo); Frahm et al. (2010), 141 (photo); Moberg & Holmåson (1984), 203 (photo); Lichen Atlas of the British Isles 3: 1127 (1998).

Most reliably confirmed by the rhizines, which are variable, more so than may be suggested in books, but which do not match the black, squarrosely-branched ("bottle-brush") rhizines of other British Physconia species.

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Images of British Lichens