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