These are five species of plants which are now illegal to buy in the uk because they have caused problems having been released into the wild and have clogged up waterways, smothering native plants and animals.
Pleese visit the link below for more details.
Azolla filiculoides Water fern
Crassula helmsii Australian swamp stonecrop
Hydrocotyle ranunculoides Floating pennywort
Ludwigia grandiflora Water primrose
Myriophyllum aquaticum Parrot's feather