Resembles Cliostomum tenerum in the apothecia having a thalline margin but the two species differ in a number of significant characters. The most obvious differences are that the thallus of C. subtenerum is sorediate and that the apothecia and ascospores are both larger than in Cliostomum tenerum. in additional Thalli of C. subtenerum abundantly fertile and pycnidia are rare, whereas C. tenerum is rarely fertile and commonly pycnidiate. Recorded rarely from shaded underhangs on siliceous rock, both on the coast, (on natural outcrops and at least once on a dry stone wall), and in montane habitats. See Friday & Coppins (2012) The Lichenologist 44(6): 723–737 and Fungi of Great Britain and Ireland.