Thallus: superficial, greenish-brown to brown, composed of rounded algal units agglomerated into irregular areoles. A thin pseudocortex composed of small-celled paraplectenchyma is overlain by dead cells. The algal layer occupies much of the thickness of the thallus. The algal cells are up to 8-10 µm in diameter, arranged in weakly defined columns.
Teleomorph: Ascomata perithecioid. Perithecia forming projections 100-200 µm in diameter, mainly one quarter to half immersed, sometimes more deeply immersed. Usually one perithecium is present per algal unit, several such units agglomerated into each areole. Involucrellum absent. Exciple brown throughout in mature perithecia, globose, 180-250 µm. Periphysoids unbranched, 20-25 µm long. Ascospores colourless, simple or sometimes also two-celled, narrowly oblong-ellipsoid, 16-22 x 7-8 µm.
Anamorph: not known.
Verrucaria obfuscans is characterized by its green-brown to brown thallus composed of rounded algal units, the rather prominent perithecia, lack of an involucrellum and narrow, medium sized ascospores.
Other saxicolous species of Verrucaria, such as V. macrostoma, V. nigrescens and V. viridula, could be confused with V. obfuscans although the latter tends to have more prominent perithecia. Anatomically the lack of an involucrellum and the pigmented exciple are features shared with V. ochrostoma but that species usually has a paler thallus comprising neatly rounded algal units.
This species was first reported for GB&I in February 2015 when it was found on an iron-stained church windowsill (Great Milton) in Oxfordshire. Subsequently it has been found to be widespread in England and has been recorded from Bedfordshire, Cambridgeshire, Huntingdonshire, Norfolk, Northamptonshire, Somerset and Wiltshire. Further records are likely now that its presence in Britain is recognised.
The first confirmed records in GB&I were from limestone mouldings (windowsills and string courses) of medieval churches where the stone was affected by metal run-off from window grilles. Subsequent records have mainly been from the same habitat but more rarely V. obfuscans has been found on limestone memorials without any metal contamination. It has also been recorded from a limestone boulder in a disused quarry. In Poland it is recorded on limestone outcrops without metal contamination.