Mycoblastus alpinus

Thallus ± spreading, film-like, effuse, with scattered to contiguous grey, low warts; prothallus grey to blackish; soralia at first scattered, punctiform, bright or citrine-yellow, bursting from low warts, often becoming efflorescent and forming irregular granular-sorediate patches, ± covering the entire thallus. Apothecia very rare, bluish black, glossy, < 1 mm diam., similar to those in M. affinis. Asci 1-spored, spores 50–80 × 30–38 µm, wall uniformly thickened, 1 or 2 aborted spores often also present in the asci. Thallus C–, K± yellow, KC± yellow, Pd–, UV– (atranorin, planaic acid, usnic acid is restricted to the soralia).

Spribille et al. (2011a, b) found that populations of Mycoblastus alpinus clustered within a strongly supported M. affinis clade, and their separation in Britain merits further study. It appears that the number of spores per ascus and the thickness of the spore wall in the two ‘species’ is not convincingly diagnostic. The thalli of both species have an identical chemistry including atranorin and planaic acid; usnic acid in M. alpinus is strictly confined to the yellow-green soralia in that species. Sparingly sorediate but fertile specimens have sometimes been assigned to M. affinis and suggest that there may be a continuum between the two ‘species.’ Sterile morphs of M. alpinus resemble Ochrolechia inaequatula, which is C+ red.