Description: Thallus of minute, peltate, usually dispersed, concave squamules 0.2(-1.0) mm diam., the upper surface densely white-pruinose, becoming pale brown to grey where rubbed, the margins raised, revealing excavate soralia bearing black, granular soredia 18-24 μm diam., which encrust the lower surface and sometimes also the underlying rock, in this case resembling a crust of cyanobacteria. Apothecia extremely rare, innate in the centre of squamules, with a concave, brown, pruinose disc. Paraphyses moniliform, the apices 2-4 µm. Ascospores not known. Photobiont chlorococcoid. Spot test: all negative. Chemistry: no lichen substances.
Note: a mainly temperate, inconspicuous lichen, certainly more widespread in northern Italy on on steeply inclined faces of man-made substrata (mortar, concrete, etc.), more rarely on calciferous schists; very much overlooked. For further details see Nordin & al. (2009). The record from Venezia Giulia is from the wall of a private house in the village of S. Lorenzo near Trieste (vidi sed non legi!).
Growth form: Crustose
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly asexual, by soredia, or soredia-like structures (e.g. blastidia)