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Physcia caesia (Hoffm.) Fürnr.


A small, foliose species, typically 1-2 cm in diameter, with narrow, convex lobes lacking marginal cilia, lobe surfaces with distinct white flecks (pseudocyphellae), soralia large, usually rounded and convex, conspicuous, first appearing as grey-blue areas on the thallus surface; apothecia rare. An evidently toxitolerant species, widespread and common, especially on urban walls and similar substrates but also in upland areas. Usually in company with Phaeophyscia orbicularis, which has similar soralia – see that species for notes on separation.

Refs: Smith et al. (2009), 700; Purvis et al. (1992), 468 (describes other morphological variants); Dobson (2005), 339 (photo); Dobson (2011), 340 (photo); Fox et al. (1993), plate 8 (photo); Jahns (1983), 252-253 (photo); Nordic Lichen Flora (2002) 2: 35, 98 (photo); van Herk & Aptroot (2004, 2013), 298-9 (photo); Wirth (1995), 2: 728, 731 (photo); Wirth et al. (2004), 151 (photo); Wirth, Hauck & Schulz (2013), 2: 873, 877 (photos, upper parasitised); Frahm et al. (2010), 134 (photo); Hansen & Anderson (1995), 54 (photo); Moberg & Holmåson (1984), 200 (photo); Holien & Tønsberg (2008), 78 (photo); Stenroos et al. (2011), 355 (photo); Brodo et al. (2001), 553 (photo); Hinds & Hinds (2007), 392-3 (photo); McCune & Geiser (2009), 270 (photo); Lichen Atlas of the British Isles 3: 1114 (1998).

 
Physcia caesia
Physcia caesia
Physcia caesia
Sandstone wall of urban building, Paisley, Renfrewshire, June 2008


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Uploaded June 2008, last updated December 2013