Images of British Lichens
Trapelia placodioides Coppins & P.James
Thallus crustose, often thick, white to pink, continuous and smooth to cracked or areolate, margin often rather obscurely lobed (± placodioid), soredia produced at areole margins or across the thallus surface, cream to yellowish, pale green or pink, rather coarse, thallus and soredia testing C+ red with bleach; apothecia rare, red-brown, with white, halo-like, residual rims of thallus (Coppins & James, see below). Widespread and locally frequent on siliceous and metalliferous rocks and stonework.
Refs: Coppins & James (1984) Lichenologist 16: 241-264; Smith et al. (2009), 907; Purvis et al. (1992), 611; Dobson (2005), 432 (photo); Dobson (2011), 438 (photo); van Herk & Aptroot (2004, 2013), 366-7 (photo); Valcárcel et al. (2003), 362-3 (photo, with apothecia, assuming correctly named); Wirth (1995), 2: 918, 919 (photo).
A variable species. Sterile Ochrolechia androgyna can be confused with this species and also tests C+ red. Generally it has a somewhat warted thallus surface and its soralia are rounded and strongly convex. Llimonaea sorediata forms pink crusts and tests C+ red, but its thallus surface is minutely crystalline and its soralia initially white and dot-like.
|On siliceous. coastal rock, Rispond, Sutherland, August 2012.|
|Variant with pale pink thallus and soredia, on montane rock, Glencoe, Argyllshire, April 2009.|
|Areolate thallus on coarse surface of stone wall, Balmaha, Stirlingshire, November 2008 (thallus det. J. Douglass, October 2008).|
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