Watsoniomyces obsoletus
Thallus inconspicuous, immersed, sometimes granular and greenish white due to superficial algae; prothallus absent.
Anamorph: not known.
Teleomorph: ascomata apothecia, 0.1-0.2(-0.35) mm diam., sessile, sometimes partially immersed, pinkish to reddish brown, finally sometimes ± black, ± closed and perithecioid at first but finally expanded with a ± flat disc True exciple persistent, colourless to creamy, becoming irregularly dentate. Epithecium red-brown, K–. Hymenium to 150 μm tall. Hypothecium orange-brown. Interascal tissue of paraphyses, simple to sparsely branched, the apices not swollen or capitate. Asci 50-70 × 12-14 μm, obpyriform, somewhat attenuated towards the apex, the apex thickened, K/I–, with a K/I+ blue gelatinous outer coat. Ascospores (14-)16-19 × (5-)6-8 μm, elongate-ellipsoidal, hyaline, with conspicuous oil drops, aseptate but sometimes appearing so, the contents I+ yellow-orange.
Chemistry: not known.
Assessed by Woods & Coppins as of Least Concern, but indicated as Nationally Scarce and possibly endemic [thus considered a species for which the UK has International Responsibility].
Almost certainly misplaced in Lecidea; Aptroot et al. (2009) suggested that it might belong in Trapelia, but molecular data is needed to elucidate the placement.
Mostly confined to SE England, with outliers in Gloucestershire and Yorkshire; the distribution largely mirrors that of chalk. BLS distribution map here.
On chalk pebbles in disturbed habitats (e.g. around rabbit burrows).