Stereocaulon leucophaeopsis
Thallus: primary thallus crustose, areolate, the areoles scattered to contiguous, to 1 mm diam., grey, spreading, with slightly tumid margins and a darker central area, remaining conspicuous especially when wet. Soralia, when present, usually confined to the margins of the areoles. Pseudopodetia and cephalodia absent, but cyanobacteria are often abundant between the areoles.
Anamorph: no information available.
Teleomorph: ascomata apothecia, rather frequent, developing from between the thalline areoles; disc to 1.5 mm diam., black, the exciple distinct. Hypothecium dark brown. Ascospores (25-) 30-38 (-40) × 6-7 μm, 3- to 5-septate, ± sub-clavate with one end ± tapered, rarely fusiform.
Chemistry: thallus K+ yellow, KC+ violet, Pd+ faintly yellow, UV+ white (atranorin and lobaric acid).
Assessed by Woods & Coppins as of Least Concern, but listed as Nationally Scarce.
Characterized by the basal, peltate areoles with dark centres which resemble the basal phyllocladia in young material of Stereocaulon vesuvianum, which, however, produce pseudopodetia. Distinguished from S. tornensis in the restriction of soredia to the margins of the areoles and the presence of lobaric acid and atranorin giving Pd+ pale yellow, UV+ white reactions.
Mainly in the west of Great Britain, rather local. BLS map here.
Usually on metal-rich rocks, occasionally on calcareous substrata.