Based on a study of photographs from 2 adjacent sites with closed crustose lichen mosaics on rock in Cardiganshire [England] taken in 1959-1960 and 1973, examples of overgrowth and equilibrium are provided. Ochrolechia parella overgrew Rhizocarpon obscuratum but reached an equilibrium on contact with Lecanora gangaleoides. L. gangaleoides was unable to overgrow islets of R. obscuratum included in its thallus. Coalescence of L. ganglaleoides small thalli to make a larger thallus was also observed. Growth rates for the species considered with calculated.