Thallus crustose, thin, pale grey to dark olive-brown , smooth to minutely cracked; apothecia, lirellate, 1-3 x 0.2-0.35mm, sessile, prominent, curved to serpentine, rarely straight; remaining persistently slit-like. Ascospores (40-)50-70(-80) × 6-8 μm, 8- to 14-septate, elongate-fusiform, with a narrow perispore. Forming large spreading patches, often along the crevices of rough barked trees. All reactions negative.
Only likely to be confused with other corticolous Opegrapha species. Opegrapha xerica is found in similar very habitats on veteran trees but has smaller, shorter apothecia with a slightly exposed disc with greenish pruina; the spores are shorter and 3-5 – septate. Non-lichenized bark fungi such as Hysterium spp. have prominent sessile, lirellate apothecia that remain persistently slit like with rounded ends, but are typically straight and shorter than those of O. prosodea.
Confined to South Pembrokeshire where it has been recorded from:
|Location||Grid Reference||Last Rec'd||Recorder||SSSI|
|Pembroke – Upton Castle||SN020045||1987||PW James & PA Wolseley|