A foliose species with light to dark grey, narrow lobes that are clearly separated from each other and become palmate and ascending at the tips. There are no pseudocyphellae or cilia. Grey lip-shaped soralia are apical but may spread along the lobe margins and become confluent.
Cortex: K+ yellow. Medulla: K-
In Scotland, Physcia dubia is mainly restricted to lowland and eastern areas where it is found on well-lit, acid, nutrient-rich enriched rocks, including gravestones. BLS distribution map
Physcia dubia is distinguished from Physcia caesia on basis of the presence of apical, lip-shaped soralia that may spread along the lobe margins rather than clusters of soralia that are laminal. Physcia dubia also has a preference for non-calcareous substrata.
scottishlichens.co.uk 