Koenigia is a new genus name, to replace some plants previously known as Persicaria . Around 35 species spread across much of the Northern hemisphere.
The larger, ornamental Koenigia species (as opposed to the original, and until recently only, species K. islandica, a rare, tiny mountain-top plant) are all floriferous, and attractive to honeybees, social wasps, hoverflies and a whole raft of other pollinators over the long flowering season. Several species are spreading in the wild, especially in western parts of Britain and Ireland; of these K. campanulata is the most widespread. It seems not to set seed, so dispersal is likely to be by means of root fragments - steps should be taken to avoid it escaping by keeping garden waste where it belongs, inside the garden fence!