Vascular Plants of North Carolina
Section: Common Name: Scientific Name: Family:
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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AuthorHouttuyn
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
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B.A. SorrieRoadside, Fire Tower Road, Aug 2014. MoorePhoto_non_natural
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