Crutarndina petractoides
Thallus cream, white or pale ochraceous, uniformly thin, somewhat immersed, ± continuous, cortex an ill-defined, superficial layer of necrotic cells mixed with sloughed bark cells, interspersed with calcium oxalate crystals; prothallus absent. Soredia and isidia absent. Photobiont Trentepohlia.
Anamorph: not known.
Teleomorph: ascomata apothecia 0.4-0.7 (-0.8) mm diam., flattened, not immersed in warts, erumpent, urceolate; ostiolar opening to 0.3 mm wide; true exciple free, colourless, ± radially stellate-lacerate, partly obscuring the black to ± densely grey-white pruinose apothecial disc; hymenium (90-) 100-120 (-130) µm, colourless, I–; hypothecium colourless; epithecium colourless to pale brown, encrusted with numerous, small, irregular crystals. Interascal tissue of filamentous, unbranched, rarely septate paraphyses; periphysoids lining the upper inner surface of the true exciple. Asci subcylindrical, with a single functional wall layer, abruptly thickened at the apex, sometimes with a minute internal apical beak, K/I–, (4-) 6- to 8-spored. Ascospores (30-) 35-50 (-55) × (7-) 8-10 µm, cylindrical to broadly cylindric-fusiform with rounded ends, remaining colourless when mature, with (7-) 9-11 (-12) strongly thickened lateral distosepta and no longitudinal septa, I+ purplish blue, with a perispore that appears to be constricted between the septa.
Chemistry: thallus C–, K–, KC–, Pd–, UV– (no lichen products detected by TLC).
Assessed by Woods & Coppins (2012) as of Least Concern, but listed under Section 2(4) of the NC (Scotland) Act 2004 and a species for which the UK has International Responsibility.
The flattened apothecia ± level with the thallus surface, with a well-developed, stellate-lacerate true exciple and pruinose disc, plus the eroding thalline margin are useful field characters separating this species from Thelotrema lepadinum.
Western Scotland, west and south-west Ireland. BLS map here.
An oceanic species on ± shaded, smooth bark, mainly of Corylus and Sorbus, more rarely of other broadleaved trees, in sheltered woodlands and boggy areas.