Strigula stigmatella var. stigmatella

This unprepossessing crustose lichen has a thin, smear-like, pale greenish-grey to grey-white crustose thallus (becoming greyer on long-storage in the herbarium) dotted with half-immersed, small black perithecia, c. 0.3mm diam., sometimes with a slightly paler zone around the ostiole apex, which are at first covered by a thin thalline layer. The thallus can sometimes appear immersed in the bark. Accurate identification requires critical and careful microscopic examination of the photobiont, asci and ascospores (see ‘similar species’ below).