Bohemian knotweed

(Reynoutria × bohemica)

Conservation Status
Bohemian knotweed
  IUCN Red List

not listed


NNA - Not applicable


not listed

Weed Status

State Prohibited Noxious Weed, Prohibited – Control

Bohemian knotweed is listed as an invasive terrestrial plant by the Minnesota Department of Natural Resources.

Wetland Indicator Status
  Great Plains

FACU - Facultative upland


FACU - Facultative upland

  Northcentral & Northeast

FACU - Facultative upland


Bohemian knotweed is an erect, 5 to 8 tall, perennial forb. It rises on usually clustered stems from a long, creeping, horizontal, underground stem (rhizome). It is a fertile hybrid between two highly invasive plants, Japanese knotweed (Reynoutria japonica) and giant knotweed (Fallopia sachalinensis), and it shares features of both of those plants. The hybrid was introduced into North American and cultivated as an ornamental. It escaped from cultivation and is now naturalized across northern United States. It is reported to be partially or fully fertile, but it spreads mostly by rhizomes and by the dispersal of plant fragments. It is found on river banks, along roadways, and in other disturbed areas. It often forms large dense colonies.

The bamboo-like stems are erect, stiff, hollow, green, and hairless. There are usually many slender branches. They are not climbing or twining. They are swollen at the nodes and are covered with a whitish waxy bloom (glaucous). Like other knotweeds (Fallopia and Persicaria), there is a sheath (ocrea) that wraps around the stem at each node. The ocrea is papery, membranous, white to tan or greenish-brown, and usually to ¼ long, sometimes up to long. It may be hairless or covered with short, fine hairs, but does not have longer bent hairs and does not have bristles at the base. It is usually deciduous.

The leaves are alternate, 2 to 12 long, and ¾ to 4 wide, larger than Japanese knotweed but smaller than giant knotweed. They are on to 1¼ long leaf stalks. The leaf blade is variable in shape, and may resemble the leaves of either parent. It may be spade-shaped, straight across (truncate) at the base, or slightly heart-shaped, indented (cordate) at the base. Both leaf shapes may appear on the same branch. They are tapered at the tip with concave sides along the tip (acuminate). They do not terminate in a sharp firm point. The upper surface is hairless. The lower surface is glaucous and has minute hairs along the veins. The margins are untoothed and may be hairless of have a short fringe of hairs.

Flowers appear from July to October. The inflorescence is an erect or spreading, 1½ to 4¾ long, cluster of flowers at the end of each branch and rising from leaf axils. It may be long, narrow, and unbranched (raceme), or short, broad, branched (panicle), and plume-like, and it may be either shorter or longer than the subtending leaf. The flowers are grouped into elongated bundles (fascicles) of 3 to 15 flowers each. There is an ocrea at the base of each fascicle. The flowers are

Each flower is to ¼ (4 to 6 mm) long and is constricted and stipe-like at the base. There are 5 petal-like tepals, 8 stamens, and 3 styles. The tepals are egg-shaped to ellipse-shaped, creamy white or greenish-white, and hairless. The outer 3 tepals are long and winged along the midrib, the inner two shorter and unwinged. All of the tepals become larger as the fruit forms. The styles are fused at the base. Each flower appears perfect, with both male and female reproductive parts, but some of the flowers are female, with nonfunctional male parts.

The fruit is a single-chambered seed capsule (achene). The achene is 1 16 to (2.6 to 3.2 mm) long, dark brown, shiny, and smooth.




5 to 8


Flower Color


Greenish-white to pink


Similar Species


Rivers; roadways and other disturbed areas




July to October


Pests and Diseases






Distribution Map



2, 3, 4, 7, 22, 28, 29, 30.




Both parent plants are native to Asia. The hybrid was introduced and cultivated as an ornamental. It escaped cultivation and is now naturalized in North America.





  Kingdom Plantae (green algae and land plants)  
  Subkingdom Viridiplantae (green plants)  
  Infrakingdom Streptophyta (land plants and green algae)  
  Superdivision Embryophyta (land plants)  
  Division Tracheophyta (vascular plants)  
  Subdivision Spermatophytina (seed plants)  
  Class Magnoliopsida (flowering plants)  
  Superorder Caryophyllanae  


Caryophyllales (pinks, cactuses, and allies)  


Polygonaceae (knotweed)  
  Subfamily Polygonoideae  
  Tribe Polygoneae  
  Subtribe Reynoutriinae  



Bohemian knotweed is a fertile hybrid between two highly invasive plants, Japanese knotweed (Reynoutria japonica) and giant knotweed (Reynoutria sachalinensis).

The parent plants were originally placed in the new genus Reynoutria in 1777. Later, the genus was merged with Fallopia, separated again, and merged again, the last time in 1988.

Species Complex
The Japanese Knotweed Complex includes Japanese knotweed, giant knotweed, and Bohemian knotweed, a hybrid of the former two.


Subordinate Taxa






Fallopia × bohemica

Polygonum × bohemicum


Common Names


Bohemian knotweed














A dry, one-chambered, single-seeded seed capsule, 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.



Gradually tapering with concave sides to a sharply pointed tip.



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



A small bundle or cluster, often sheathed at the base, as with pine needles.



Pale green or bluish gray due to a whitish, powdery or waxy film, as on a plum or a grape.



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



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



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



Referring to a flower that has both male and female reproductive organs.



On plants: The stalk of a leaf blade or a compound leaf that attaches it to the stem. On ants and wasps: The constricted first one or two segments of the rear part of the body.



An unbranched, elongated inflorescence with stalked flowers. The flowers mature from the bottom up.



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



Growing in a spiral usually around a stem of another plant that serves as support.

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    Bohemian knotweed      

Plume-like Inflorescence

    Bohemian knotweed      
  Spade-shaped Leaf  
    Bohemian knotweed      

Shallowly Heart-shaped Leaf

    Bohemian knotweed      



City of Boulder



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Other Videos
  Emerging Bohemian Knotweed

Apr 21, 2020

Ever wondered what Bohemian knotweed looks like as it starts to emerge in the spring? Check out this video by the Invasive Species Council of Metro Vancouver (ISCMV) to see new growth of knotweed, emerging alongside last years dead knotweed canes.

  Identification of Invasive Perennial Knotweeds
Wisconsin First Detector Network

Jun 11, 2018

Learn how to identify three invasive perennial knotweeds in Wisconsin from the Wisconsin First Detector Network.




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