Previous British records of Calicium corynellum are now known to be of Calicium viride growing on rocks near epiphytic colonies of Calicium viride. However, true Calicium corynellum may occur in overhanging siliceous rocks in shaded and humid situations in upland Britain. Calicium corynellum differs from Calicium viride in its short-stalked, greyish white pruinose ascomata (C. viride has long stalks and a brown pruina), distinctly narrower spores compared with C. viride, and the leprose bright green thallus which is granular to verrucose in C. viride.
See Olariaga, Pérez-Ortega & Wedin (2020) Lichenologist 52, 333–335 Link
No confirmed locations in Britain.