Caloplaca squamuloisidiata van den Boom & V. J. Rico is described as new to science. It is a saxicolous species, pale green to grey, with olivaceous patches, with a rimose-areolate, squamulose, lobulate and isidiate thallus, growing on inland exposed acid rock faces in the western half of the Iberian Peninsula in the Mediterranean region. Its ecology and distribution, and the lichen communities in which it was found are presented. A key to the isidiate and granular-isidiate Caloplaca species in Western Europe is also included.