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Similar but less problematic plants:
Aruncus dioicus Form
Viburnum lentago Flowering form
Reynoutria japonica is often confused with:
Persicaria orientalis Flower and Leaves
Native alternative(s) for Reynoutria japonica:
Clethra alnifolia Clethra alnifolia
Itea virginica Itea virginica
Viburnum dentatum Viburnum dentatum
Plants that fill a similar niche:
Nandina domestica Growing Form
Paulownia tomentosa Paulownia tomentosa
Persicaria perfoliata Stem and Leaves

Reynoutria japonica

Previously known as:

  • Fallopia cuspidatum
  • Fallopia japonica
  • Pleuropterus cuspidatus
  • Polygonum cuspidatum
Phonetic Spelling
RAY-nu-tree-AH juh-PON-ih-kuh
This plant is an invasive species in North Carolina
Description

Japanese knotweed is an herbaceous, perennial, weed in the buckwheat family (Polygonaceae).  It is native to eastern Asia, and it is an invasive species in North Carolina. It quickly grows 10 to 13 feet tall and forms dense stands 3 to 20 feet wide that crowd out native plants.

The erect, hollow stems of Japanese knotweed have swollen nodes that give it the look of bamboo, but Japanese knotweed is not related to bamboo. It dies to the ground in winter and new growth is reddish-brown. Flowering occurs on erect panicles in late summer to fall. Older stems become woody near the ground. It spreads by strong underground stems (rhizomes) that can damage foundations, roads, walls and other structures. Cut or broken stems will root if left on moist soil or put directly into water. 

Japanese knotweed dominates an ecosystem and can be particularly problematic in riparian areas where it lowers the quality of habitat for fish and wildlife. Also, dead stems can accumulate and cause flooding or it can contribute to streambank erosion. In parts of the UK where this weed is a problem, its presence on a property lowers the property value. Avoid adding this plant to a landscape.

Quick ID Hints:

  • Upright stems are hollow and resemble bamboo.
  • Leaves are heart to triangular shaped and alternate.

Insects, Diseases and Other Plant Problems: Weedy and listed as invasive by the NC Invasive Plant Council. Do not plant. See native alternatives to the left.

See this plant in the following landscape:
Cultivars / Varieties:
  • var. compacta
    Less weedy than the species but still not recommended
var. compacta
Tags:
#invasive#edible weed#high maintenance#stream banks#fast growing#aggressive#disturbed areas#edible stems#roadside#weed#hs303
 
Cultivars / Varieties:
  • var. compacta
    Less weedy than the species but still not recommended
var. compacta
Tags:
#invasive#edible weed#high maintenance#stream banks#fast growing#aggressive#disturbed areas#edible stems#roadside#weed#hs303
  • Attributes:
    Genus:
    Reynoutria
    Species:
    japonica
    Family:
    Polygonaceae
    Uses (Ethnobotany):
    Used in Asian herbal medicine
    Life Cycle:
    Perennial
    Country Or Region Of Origin:
    Eastern Asia
    Edibility:
    Young stems are edible with a sour rhubarb flavor.
    Dimensions:
    Height: 10 ft. 0 in. - 13 ft. 0 in.
    Width: 3 ft. 0 in. - 20 ft. 0 in.
  • Whole Plant Traits:
    Plant Type:
    Edible
    Herbaceous Perennial
    Weed
    Habit/Form:
    Arching
    Growth Rate:
    Rapid
    Maintenance:
    High
  • Cultural Conditions:
    Light:
    Full sun (6 or more hours of direct sunlight a day)
    Soil Drainage:
    Moist
    Occasionally Wet
    Available Space To Plant:
    6-feet-12 feet
    12-24 feet
  • Fruit:
    Fruit Color:
    Cream/Tan
    Fruit Type:
    Achene
    Fruit Length:
    < 1 inch
    Fruit Width:
    < 1 inch
    Fruit Description:
    Small winged triangular achene with small shiny dark brown to black triangular shaped seeds.
  • Flowers:
    Flower Color:
    Cream/Tan
    Green
    White
    Flower Inflorescence:
    Panicle
    Spike
    Flower Bloom Time:
    Fall
    Summer
    Flower Petals:
    4-5 petals/rays
    Tepals
    Flower Size:
    < 1 inch
    Flower Description:
    Small creamy-white flowers with 5 tepals in 3-6 inch long erect panicles from the leaf axils in later summer to fall. Male and female flowers are on separate plants with the male flowers being more erect and the female flowers drooping.
  • Leaves:
    Leaf Color:
    Green
    Red/Burgundy
    Leaf Type:
    Sheath
    Simple
    Leaf Arrangement:
    Alternate
    Leaf Shape:
    Deltoid
    Elliptical
    Subcordate
    Leaf Margin:
    Entire
    Hairs Present:
    No
    Leaf Length:
    3-6 inches
    Leaf Width:
    1-3 inches
    Leaf Description:
    3 to 7 inches long and 2-4 inches wide broadly oval, to triangular, sharply pointed, alternate leaves with truncated bases and entire margins. Leaves are dark green on top and light green below with reddish veins. Where they meet the stem there is a sheath-like structure called an ocrea. New growth is red.
  • Stem:
    Stem Color:
    Brown/Copper
    Green
    Red/Burgundy
    Stem Is Aromatic:
    No
    Stem Cross Section:
    Round
    Stem Description:
    Stems are green to reddish-brown large, hollow, slightly rideged lengthwise, jointed and mottled. They resemble bamboo and remain after the plant has died back to the ground. Older stems become woody near the ground.
  • Landscape:
    Problems:
    Invasive Species
    Weedy