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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.

Trapelia placodioides
On siliceous. coastal rock, Rispond, Sutherland, August 2012.
 
Trapelia placodioides
Trapelia placodioides
Variant with pale pink thallus and soredia, on montane rock, Glencoe, Argyllshire, April 2009.
 
Trapelia placodioides
Areolate thallus on coarse surface of stone wall, Balmaha, Stirlingshire, November 2008 (thallus det. J. Douglass, October 2008).


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