Megalaria pulverea  

Thallus effuse, thin, sometimes ± evanescent. Soralia usually extensively developed, large, effuse, grey-white to glaucous, granular, sometimes coalescing to form an almost continuous, sorediate crust. Soredia grey-green, bluish or yellowish green, 40-100 μm diam. Photobiont Dictyochloropsis, with cells 5-14 μm diam.
Anamorph: not known.
Teleomorph: ascomata apothecia, 0.5-2.2 mm diam., rare, flat, sometimes convex and contorted, grey-brown to black. Thalline exciple absent. True exciple distinct, colourless or pale brownish in the upper part, sometimes concolorous with the epithecium at the upper outer edge, the hyphae coherent in K, 2-3 μm diam., each with a thick gel coat. Epithecium dark green, K+ green intensifying, N+ red, sometimes with additional violet K+ green patches. Hymenium 45-75 μm tall, hyaline. Hypothecium (and exciple) hyaline or pale brown in the uppermost and/or lowermost parts, with minute, colourless crystals that do not dissolve in K or N. Interascal tissue composed of thick-walled anastomosing paraphyses 1.8-2 (-2.5) μm diam., the apices clavate, 3-4 μm diam. and surrounded by dark pigment. Asci with the apical cushion narrow, ± surrounded by a thin, dark blue zone in I. Ascospores 10-16 (-19) × 4.5-6.5 μm, broadly to fusiform-ellipsoidal, with a ± median septum, hyaline, the walls rather thick, smooth, without an epispore, gelatinous sheath or appendages.
Chemistry: thallus K+ yellow, Pd+ red, often Pd– or faint yellow, UV– (atranorin, zeorin and usually fumarprotocetraric acid).