Myriospora smaragdula (Wahlen. ex Ach.) Nägeli ex Uloth.
Acarospora smaragdula (Wahlenb.) A. Massal.
Thallus crustose, 1-5 cm wide; contiguous convex areoles, 1-1,5 mm wide, forming a well-developed pavement-like continuous crust, typically brown-yellow, brown-cream, light brown-green, yellow-brown often of a waxy appearance. Apothecia 3-7 per areole; thalline margin absent to well-developed, most often deformed by compression, black ; disc small, dark or black-brown, 0.2-0.3 mm diam., plane, smooth, occasionally widening to 0.7 mm diam. Spores somewhat keyed-up, small and nearly 100 in each ascus, broadly elliptical, 2-5 x 1-2 µm. C-, K + red, KC + red, P + yellow (variable according to the authors because there are several chemoforms). Photobiont: Chlorococcales. Species not especially coastal and rather with northern tendencies but rather frequent on the very exposed acid siliceous rocks.
N.B. At the seaside on rocks rich in iron and not very acidic see: Myriospora rhagadiza which has fewer apothecia with a sharper margin. NB There is great confusion in the taxonomy and interpretations of this "species" which varies greatly depending on its substrate and its environment and it is preferable to consider it as a group of taxa "to be sorted out", however the yellow tints. a little greenish to ivory ochraceous characterizes this group quite well.