Polygonum capitatum

Persicaria capitata, the pink-headed persicaria, pinkhead smartweed, pink knotweed, Japanese knotweed, or pink bubble persicaria, is an Asian species of plants in the genus Persicaria within the Polygonaceae (US: buckwheat) family. It is native to Asia (China, South Asia, Indochina) and grown as an ornamental in other countries. It has become naturalized in Australia, South Africa and a few scattered locations in the Americas.