Rhynchostegium megapolitanum was observed during a study of the effects of the invasive nonnative Rosa rugosa in a sand dune. The vascular as well as the epiphytic and epigeic cryptogam vegetation was recorded., and soil properties were measured. Epihytic lichens were abundant on dead or dying branches of Rosa rugosa scrubs, under which the stable substrate and high light exposure provided growth conditions for an epigeic community dominated by lichens and bryophytes. The occurrence of the rare bryophyte Rhynchostegium megapolitanum is discussed.