Platismatia glauca
Thallus 1-6 (-15) cm diam., often forming extensive patches, rather thin and papery, especially when dry. Lobes to 1.5 cm wide, wavy, irregularly indented, margins ascending, entire or sub-lobulate, often with marginal clusters of simple to coralloid, much branched, isidia or in part, granular soredia. Upper surface pale to dull grey, often with a brown tinge or totally tinged brownish (in exposed sites), ± unchanged or ± greenish in colour when wet, smooth to wrinkled or slightly ridged, without pseudocyphellae. Lower surface entirely black, or brown or white (shade morphs), especially towards the margin, with few to many, scattered, simple or branched rhizines. Photobiont trebouxioid.
Anamorph: conidiomata pycnidia, marginal, immersed. Conidia cylindrical, not swollen at apices.
Teleomorph: ascomata apothecia, very rare, 5-9 mm diam., marginal, with a red-brown disc. Thalline exciple thin, ± excluded at maturity. Hymenium I+ blue. Hypothecium thin, I+ blue, usually lacking algae below. Asci 8-spored, Lecanora-type. Ascospores 3.5-8.5 × 3-5 μm.
Chemistry: cortex K+ yellow (atranorin), medulla C–, K–, KC–, Pd–, UV– (caperatic acid).
Assessed by Woods & Coppins (2012) as of Least Concern. A common and widespread species.
A very variable species; the lobes may be elongate, ± entirely erect with much dissected, coralloid-lobulate isidiate margins or ± closely adpressed with only the margins upturned with granular-sorediate isidia. The isidia or soredia are mainly confined to the margins but, on occasion, may also occur in small patches or widely dispersed on the upper surface.
Tuckermanopsis chlorophylla has brown lobes turning olive-green when wet. Cetrelia olivetorum has scattered, dot-like pseudocyphellae on the upper surface (×10), a C+ pink medulla and finely sorediate margins. Parmotrema perlatum and related species have marginal cilia and a different chemistry.
Throughout the British Isles and Ireland, more common in the north and west. BLS map here.
On trees, rocks and soil, especially acidic, leached habitats; particularly common on Betula bark.