Reynoutria japonica
Common Name(s):
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:
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- var. compacta
Less weedy than the species but still not recommended
- var. compacta
- var. compacta
- Tags:
- Cultivars / Varieties:
-
- var. compacta
Less weedy than the species but still not recommended
- var. compacta
- var. compacta
- Tags:
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-
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.
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Whole Plant Traits:
- Plant Type:
- Edible
- Herbaceous Perennial
- Weed
- Habit/Form:
- Arching
- Growth Rate:
- Rapid
- Maintenance:
- High
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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
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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.
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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.
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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.
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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.
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Landscape:
- Problems:
- Invasive Species
- Weedy
