Japanese knotweed

(Fallopia japonica var. japonica)

               
Conservation Status

IUCN Red List

not yet assessed

Japanese knotweed

NatureServe

NNA - Not applicable

SNA - Not applicable

Minnesota

not listed

Wetland
Indicator
Status

Great Plains

FACU - Facultative upland

Midwest

FACU - Facultative upland

Northcentral & Northeast

FACU - Facultative upland

Weed Status

Specially Regulated Plant

Invasive

 
Nativity

Native to Japan, Korea, Taiwan, and China. Introduced and naturalized in the United States and Canada. Introduced; escaped cultivation.

 
Occurrence

 

 
Habitat

Moist to moderate moisture. Woods, fence rows, roadsides. Full to partial sun.

 
Flowering

August to September

     
Flower Color

White to greenish

     
Height

3½ to 10

     

Identification

This is a 3½ to 10 tall, erect, perennial forb that rises from a long, horizontal, spreading, underground stem (rhizome). It often forms a dense thicket. It spreads aggressively and can form colonies up to an acre in size.

The stems are annual, erect or arching, stout, hollow, and hairless. They are unbranched or few-branched, round in cross section, somewhat zigzagged, and swollen at the nodes. They are light green, often with reddish spots, or reddish-brown. Above each node the stem is surrounded by a papery, fringed sheath (ocrea). Older stems are finely ridged.

The leaves are alternate, deciduous, stalked, broadly oval, 3 to 6 long, and 2 to 4¾ wide. The base of the leaf is usually broad and straight across, sometimes slightly heart-shaped. The blade tapers to a point at the tip with concave sides along the tip. The upper surface is hairless. The lower surface is minutely rough-hairy along some of the veins. The hairs are not visible without a hand lens. The margins are untoothed.

The inflorescence is a branched, elongated, erect, 3 to 6 long cluster (panicle) of numerous flowers rising from upper leaf axils.

In its native range each plant produces either flowers with both fertile male and fertile female parts or flowers with infertile male and fertile female parts. In North America only the latter have been introduced.

The flowers are white or greenish-white and bell-shaped. There are 5 tepals consisting of 2 small inner petals and 3 larger, outer, keeled, petal-like sepals. The tepals are fused at the base. Male flowers have 6 to 8 reduced, nonfunctional stamens (staminodes). Female flowers have 3 spreading styles.

The fruit is a shiny, dark brown, hairless, three-angled, 1 16 to long nut (achene).

 
Similar
Species

 


Distribution Distribution Map   Sources: 2, 3, 4, 7, 22, 28.

Comments

Propagation
In North America only plants with fertile female and infertile male plants have been introduced. The plant spreads by an extensive rhizome system. Having no fertile male flowers the plant cannot produce by reseeding. Fragments of stem or rhizome can produce new plants. Dispersal occurs when plant fragments are washed downstream or are inadvertently transported in dirt by humans.


Taxonomy

Family:

Polygonaceae (buckwheat)

 

Subfamily:

Polygonoideae

 

Tribe:

Polygoneae

 
Synonyms

Pleuropterus cuspidatus

Pleuropterus zuccarinii

Polygonum cuspidatum

Polygonum cuspidatum var. compactum

Polygonum zuccarinii

Reynoutria japonica

 
Common
Names

fleeceflower

Japanese knotweed

Mexican bamboo


 

 

 

 

 

 

 

 

 

 

Glossary

Achene

A dry, one-chambered, single-seeded fruit, formed from a single carpel, with the seed attached to the membranous outer layer (wall) only by the seed stalk; the wall, formed entirely from the wall of the superior ovary, does not split open at maturity, but relies on decay or predation to release the contents.

 

Axil

The upper angle where a branch, stem, leaf stalk, or vein diverges.

 

Keeled

Folded, as in a grass blade, or with a raised ridge, as in a grass sheath; like the keel of a boat.

 

Node

The small swelling of the stem from which one or more leaves, branches, or buds originate.

 

Ocrea

A sheath around the stem at the base of a petiole formed from the stipules; a feature of many members of the Polygonaceae.

 

Panicle

A pyramidal inflorescence with a main stem and branches. Flowers on the lower, longer branches mature earlier than those on the shorter, upper ones.

 

Rhizome

A horizontal, usually underground stem. It serves as a reproductive structure, producing roots below and shoots above at the nodes.

 

Staminode

A modified stamen that produces no pollen. It often has no anther.

 

Tepal

Refers to both the petals and the sepals of a flower when they are similar in appearance and difficult to tell apart. Tepals are common in lilies and tulips.

       

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Plant

  Japanese knotweed   Japanese knotweed
       

Inflorescence

  Japanese knotweed    
       

Leaves

  Japanese knotweed   Japanese knotweed
       
  Japanese knotweed   Japanese knotweed
       

Stem

  Japanese knotweed    
       
       

 

Camera

     

Slideshows

   
  Fallopia japonica
Susanne Wiik
 
  Fallopia japonica  
 
About

Parkslirekne, Japanese knotweed

 
     
  Japanese Knotweed
Wez Smith
 
  Japanese Knotweed  
 
About

Japanese Knotweed (Fallopia japonica).

 
     
  Japanese Knotweed
Andree Reno Sanborn
 
  Japanese Knotweed  
     
  Japanese Knotweed Identification
Invasive Weeds Agency
 
   
 
About

Published Jan 25, 2013

How to identify Japanese knotweed (Fallopia japonica) throughout the year. Find more info at Invasive Weeds Agency's website.

 
     

 

slideshow

     

Visitor Videos

   
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Other Videos

 
  The plant that breaks through concrete
One Minute Environment
 
   
 
About

Uploaded Jun 30, 2011

The Japanese Knotweed (Fallopia japonica) is by law banned from Switzerland. It spreads nevertheless. It can breakt through concrete and pushes out native plants.

 
     
  Japanese Knotweed
backyardfarmer
 
   
 
About

Uploaded May 20, 2011

UNL Extension Educator Nicole Haxton shows us what Japanese Knotweed looks like and discusses strategies to control it.

 
     
  Invasive Species: Japanese Knotweed
Cindy Sandeno
 
   
 
About

Published on Jun 22, 2012

Potomac Highlands Cooperative Weed and Pest Management Area short film about the invasive species: Japanese Knotweed. Identification, the problems, and treatment of Tree of Heaven.

 
     

 

Camcorder

         

Visitor Sightings

   
Report a sighting of this plant.

Debbie
8/15/2018

Location: Grant (Washington County)

Starting to see it all over the place!


Tia
4/20/2016

Location: Shelton Washington

pain in the button, taken over acre


     
     
 

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