A distinctive, crustose species with a milk-chocolate brown thallus that may be olive-green in shade. The thick thallus is clearly raised above the substratum. It is divided by cracks into clearly separated angular islands and sometimes looks almost squamulose. The relatively large perithecia are over half immersed.
Verrucaria macrostoma is found locally in the east of Scotland on calcareous sandstone, mortar and limestome, including vertical saxicolous substrata in churchyards, and probably prefers some nutrient-enrichment. BLS distribution map
scottishlichens.co.uk 