Myriospora smaragdula (Ach.) UlothThallus crustose, episubstratic, yellowish, yellowish brown or pale brown (yellow-green on copper-rich rocks), areolate, the areoles dispersed or in small groups, more or less flat, rounded to irregular, the fertile ones (0.4-)0.6-2(-3) mm wide, epruinose. Epinecral layer 5-20 µm thick; cortex 30-50 µm thick, paraplectenchymatous, the uppermost cells opaque-yellowish, with a dense layer of crystals (norstictic acid), the lower part intergrading into a prosoplectenchyma that merges with the medulla; algal layer appearing continuous on a thick section, but actually interrupted by thick anticlinal bundles of medullary hyphae; lower cortex absent. Apothecia (1-)3-6(-8) per areole, immersed, 0.1-0.2(-0.4) mm across, with a usually sunken, at first punctiform, later somewhat expanded, dark brown to brown-black, usually rough, epruinose disc and a thin thalline margin. Proper exciple colourless, to 35 µm thick laterally, to 50 µm thick in upper part; epithecium reddish brown; hymenium colourless, (60-)120-250(-280) µm high, hemiamyloid, IKI+ reddish brown; paraphyses 1-1.5 µm thick at mid-level, the apical cells to 3.5 µm wide; hypothecium colourless to greyish, IKI+ blue. Asci 100-200-spored, clavate, the apical dome K/I-, up to 150 × 31 µm. Ascospores 1-celled, hyaline, narrowly ellipsoid to bacilliform, 2.5-5 x 1-1.5 µm. Photobiont chlorococcoid. Spot tests: thallus K+ yellow then rapidly blood-red (red crystals in microscope slides), KC-, C-, P- or P+ faintly yellow, UV-. Chemistry: norstictic acid.