Cresponea premnea
Thallus crustose, whitish to greyish, continuous, smooth, thin, effuse, usually poorly developed and sometimes evanescent, occasionally delimited by a dark brown hypothallus line. Soralia and isidia absent. Photobiont Trentepohlia.
Anamorph: conidiomata pycnidia, 60-100 μm diam., occasional, mostly arranged in lines or groups, black, half-immersed to sessile. Conidia 3.5-4.6 × ca 0.8 μm, bacilliform.
Teleomorph: ascomata apothecia, 0.4-1.5 (-2) mm diam., disciform, black, sessile, slightly constricted at the base. Disc sometimes thinly grey-green-pruinose, especially in young apothecia. Thalline exciple absent. True exciple persistent, prominent, ± crenulate. Hymenium 60-120 µm tall, I+ reddish, K/I+ blue. Subhymenium 25-40 µm thick, brownish in the inner part and hyaline in the upper part, I+ and K/1+ blue. Interascal tissue composed of pseudoparaphyses, 1.5-2 µm diam., the apical cell thickened (to 4-5 µm), with a distinct dark brown cap which is formed in the inner part of the cell wall. Asci 60-75 (-80) x 12-13 µm, cylindrical to cylindric-clavate, short-stalked, thick-walled and fissitunicate, 8-spored. Ascospores arranged bieriately, 18-25 × 4.5-6 (-7) μm, cylindric-fusiform, with pointed ends, often curved, (4- to) 5- (to 7-) septate, often appearing slightly distoseptate, hyaline, thick-walled, smooth, without an epispore, gelatinous sheath or appendages.
Chemistry: no lichen products detected by TLC.
Assessed by Woods & Coppins (2012) as of Least Concern, but listed as of International Responsibility and a Priority Taxon for Biodiversity in Scotland.
Specimens on rocks have been named as Cresponea premnea var. saxicola (Leight.) Egea & Torrente (1993), and occur throughout the distribution range of the species, although considerably rarer.
Scattered and most frequent in S and SW England, rare in N England and W Scotland, also in Wales and Ireland. BLS map here.
On dry, rough, usually well-lit bark of mature Quercus, Taxus and (rarely) Fagus, often occurring with Lecanographa lyncea, in ancient, usually open, parklands or forests, more rarely on hard, acid rocks under dry overhangs. It is the dominant species of the post-climax Lecanactidetum premneae association on old trees.