The authors report on the occurrence, distribution and invasion potential of Rubus armeniacus, a bramble species of Caucasian origin, in Hungary. The first verified records of the species are from the 1990s. It has established strong populations in ruderal habitats mainly around Budapest and some other cities, whereas its competiveness is rather weak in closed non-lowland forests rich in native bramble species. In terms of conservation, it constitutes a real threat to the vegetation of Pannonian sandy habitats. The results of this study also emphasize the importance of recognising "nonnative cryptic species" for ecology and conservation biology.