Giant knotweed (Fallopia (Polygonum) sachalinensis (sachalinense)) is an invasive plant. It is a native of Japan and was first detected in Eastern USA in 1894.
Giant knotweed is an herbaceous perennial, strongly rhizomatous, growing over 12 feet tall. Once established, giant knotweed spreads by rhizomes, enabling this species to dominate and out compete native or beneficial plants. Research indicates that giant knotweed produces allelochemicals from the roots, which aids in the aggressiveness and rapid colonization strategy.