Phlyctis argena (Spreng.) Flot.

    Thallus crustose, to 10-20 cm across, more or less thick, smooth to slightly cracked, whitish, cream white tinged glaucous, white-greenish, white-greyish, covered with white granular soredia, white-greenish more or less in smears or clustered on potentially the whole surface of the thallus, sometimes in minute piles, resembling eroded warts, prothallus glossy, whitish. Apothecia very rare, isolated at the bottom of warts, irregular to rounded, 0.2-0.5 mm diam., disc whitish, pruinose. Ascii 1-spored. Ascospores colourless, broadly ellipsoid, muriculate, 80-140 x 25-50 µm. Soralia and thallus: C-, K+ yellow > red, KC+ red, Pd+ orange, UV-. Common, on tree barks (to the exception of resinous trees) in moist and shaded areas, seldom on rocks and in that case, not to be confused with sterile forms of Pertusaria lactescens of which chemical spot tests are identical except Pd+ golden yellow, isidia not in heaps, and which are less grey-greenish and more cream-ochre.*