Caloplaca teicholyta (images of British lichens)

Thallus white to whitish grey, forming irregular to rounded crusts, irregularly and rather obscurely lobed (placodioid) at the margins, surface scurfy, eroding towards the centre to become granular-sorediate (i.e. soralia not clearly delimited); apothecia uncommon, orange to red-brown, scattered and initially immersed in the thallus surface. Only the apothecia give the purple reaction with potassium hydroxide that generally characterises Caloplaca species. Locally common in the south and east, more restricted to the coast in the west, on calcareous rocks, walls and monuments; northern records said to be less certain.

Refs: Smith et al. (2009), 271; Purvis et al. (1992), 157; Dobson (2005), 107 (photo); Dobson (2011), 116 (photo); van Herk & Aptroot (2004), 106-107 (photo); Wirth (1995), 1: 214, 215 (photo); Wirth et al. (2004), 239 (photo); Puntillo (1996), plate 9 (photo); Lichen Atlas of the British Isles 6: 281 (2001).

When lacking apothecia, C. teicholyta can be confused with Diploicia canescens or Dirina massiliensis, with which it may grow.

lastdragon.org

Images of British Lichens