Cliostomum subtenerum
Thallus effuse, thin and discontinuous, occasionally thicker (to 400 µm thick), white, non-corticate. Soralia 100-300 µm diam, pale green, covering most of the thallus, soon confluent and appearing effuse; soredia ca 200 µm diam, farinose. Photobiont chlorococcoid, cells 8–12 µm diam.
Anamorph: conidiomata pycnidia, rare; flesh-coloured to pale brown, immersed in thicker areas of the thallus. Conidia 7–8 x 15–20 µm, ellipsoidal to bacilliform.
Teleomorph: ascomata apothecia, 400-800 µm diam, scattered, sessile, becoming tuberculate and then to 1.2 mm diam; disc pinkish brown to pale brown with paler margin, slightly convex, soon becoming tuberculate with excluded margin. Excipulum composed of conglutinate radiating hyphae 5 µm diam; internally colourless to yellow-brown with grey-brown granular intrusions not dissolving in K, outer cells with brown pigment, becoming colourless in K. Hymenium 40–45 µm tall, hyaline, I+ blue, epihymenium brown, granular, becoming colourless in K. Hypothecium hyaline, composed of randomly orientated hyphae. Interascal tissue of paraphyses 1.5–2 µm diam, moderately branched and anastomosing, apices to 3 µm diam, pigmented cap absent. Asci ca 30 x 12 µm, clavate, Bacidia-type. Ascospores (10–)12–15(–20) x 3–4 µm, narrowly ellipsoidal to fusiform, hyaline, 0- or 1-septate, often slightly curved.
Chemistry. Thallus and soredia C--, K+ yellow, Pd+ orange, UV+ dull yellow; atranorin, stictic acid and zeorin by TLC.
Cliostomum subtenerum resembles C. tenerum in the ascomata having a thalline margin but the two species differ in a number of significant characters. The most obvious differences are that the thallus of the new species is sorediate and that the apothecia and ascospores are both larger [100–200 (–500) µm diam and 7–10 (–15) x (1.5–) 2–3 µm respectively in C. tenerum]. That species also has a wider ecological amplitude, occurring in underhangs in montane situations and in coastal habitats, as well as a different chemistry (zeorin absent in C. tenerum). An additional difference is that all collections of C. subtenerum are abundantly fertile and pycnidia are rare, whereas C. tenerum is rarely fertile and commonly pycnidiate.
Known from Scotland (Stirlingshire) and Wales (Anglesey).
Reported from shaded underhangs on schistose rock.