Vascular Plants of North Carolina
Account for Japanese Knotweed - Reynoutria japonica   Houttuyn
Members of Polygonaceae:
Members of Reynoutria with account distribution info or public map:
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Section 6 » Family Polygonaceae
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DistributionAcross most of the state, with some gaps. Cultivated at Biltmore (Buncombe County) as early as 1897; first found outside of cultivation in 1949 in Forsyth County. Certainly will be found in additional counties.

Native of eastern Asia; in N.A. essentially throughout southern and maritime Canada south to GA, LA, OK, CA.
AbundanceGenerally fairly common to locally common, and disturbing -- increasing considerably and becoming a major invasive species. Populations should be eradicated where found.
HabitatRoadsides, railroad margins, waste places, disturbed ground, fields, ditches.
PhenologyFlowering and fruiting May-October.
IdentificationJapanese Knotweed is easily identified by its robust size to 6 feet tall (or more) and semi-woody stems -- with a wide-branching appearance. The leaves are large, broadly elliptical, rapidly tapered to the tip, and squared off at the base (truncate). The inflorescences are in leaf axils, multi-branched, with numerous small white flowers; these racemes distinctively grow erect (vertically) from the axils.
Taxonomic CommentsThis species has typically been known as Polygonum cuspidatum. A hybrid between R. japonica and R. sachalinensis has been reported from the NC mountains. See Weakley (2018) or FNA for ID criteria.

Other Common Name(s)
State RankSE
Global RankGNR
State Status
US Status
USACE-agcpUPL link
USACE-empFACU link
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B.A. SorrieRoadside, Fire Tower Road, Aug 2014. MoorePhoto_non_natural
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