Lindernia dubia (L.) Pennell, a North American species, is still a rare and ephemerical neophyte in the Netherlands, but is invading the country rapidly now. We expect it to become a threat to plant biodiversity in Dutch wetlands. To describe its ecological and phytosociological position and assess its possible risk status we investigated known sites in the Netherlands. Being a pioneer species on open, muddy soil, more or less rich in nutrients, more or less acid, it occurs in different phytosociological classes: Littorelletea uniflorae, Phragmitetea, Isoeto-Nanojuncetea and Bidentetea tripartitae. We consider the species as possibly harmfull to vegetations belonging to the Littorelletea uniflorae and some associations of the Isoeto-Nanojuncetea, as those vegetations are already threatened by drainage and athmospheric deposition of nitrogen; they contain several species of the Dutch Red list for vascular plants and the size and growth rate of many characteristic plants makes them vulnerable to outcompeting by Lindernia dubia.