AimWe use data from 13 mountain regions and surrounding lowland areas toidentify (1) the origins, traits and cultural uses of alien plant species that establishin mountains, (2) the alien species that are most likely to be a threat and (3) howmanagers might use this information to prevent further invasions.LocationAustralia, Canada, Chile, India, New Zealand, South Africa, Spain,Switzerland, USA.MethodsLists of alien species were compiled for mountains and theirsurrounding or nearby lowlands. Principal co-ordinates analysis was performedon a matrix of similarities created using presence/absence data for alien species.The significance of differences between means for (1) similarity metrics oflowland and mountain groups and (2) species traits of lowland and mountainalien floras was determined usingt-tests. In seven of the 13 mountain regions, listsof alien species undergoing management were compiled. The significance ofdifferences between proportions of traits for species requiring and not requiringmanagement input was determined with chi-square tests.ResultsWe found that the proximal lowland alien flora is the main determinantof a mountain region’s alien species composition. The highest similarities betweenmountain floras were in the Americas/Pacific Region. The majority of alienspecies commonly found in mountains have agricultural origins and are of littleconcern to land managers. Woody species and those used for ornamentalpurposes will often pose the greatest threat.Main conclusionsGiven the documented potential threat of alien species invadingmountains, we advise natural resource managers to take preventive measuresagainst the risk of alien plant invasion in mountains. A strategy for preventionshould extend to the surrounding lowland areas and in particular regulate theintroduction of species that are already of management concern in other mountainsas well as climatically pre-adapted alien mountain plants. These may well becomemore problematic than the majority of alien plants currently in mountains.