Bohemian knotweed

(Fallopia × bohemica)

               
Conservation Status

IUCN Red List

not listed

Bohemian knotweed

 

NatureServe

NNA - Not applicable

Minnesota

not listed

Wetland
Indicator
Status

Great Plains

FACU - Facultative upland

Midwest

FACU - Facultative upland

Northcentral & Northeast

FACU - Facultative upland

Weed Status

Not listed in Minnesota

Nativity

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

Occurrence

Uncommon

Habitat

Rivers; roadways and other disturbed areas

Flowering

July to October

 
Flower Color

Greenish-white to pink

 
Height

5 to 8

 
 
Identification

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 (Fallopia japonica var. 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.

 
Similar
Species

 

 
Distribution Distribution Map  

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

 
Comments

Taxonomy
This plant is a fertile hybrid between two highly invasive plants, Japanese knotweed (Fallopia japonica var. japonica) and giant knotweed (Fallopia 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. There is currently confusion, or at least disagreement, about the correct genus name. Both names, Fallopia × bohemica and Reynoutria × bohemica, are now in use.

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

 
Taxonomy

Family:

Polygonaceae (buckwheat)

 

Subfamily:

Polygonoideae

 

Tribe:

Polygoneae

 
Parents

Japanese knotweed (Fallopia japonica var. japonica) and giant knotweed (Fallopia sachalinensis)

 
Synonyms

 

 
Common
Names

Bohemian knotweed

   

 

 

 

 

 

Glossary

Achene

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.

 

Acuminate

Gradually tapering with concave sides to a sharply pointed tip.

 

Axil

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

 

Fascicle

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

 

Glaucous

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

 

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.

 

Perfect

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

 

Petiole

The stalk of a leaf blade or compound leaf that attaches the leaf blade to the stem.

 

Raceme

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

 

Rhizome

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

 

Twining

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

       
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Branch

  Bohemian knotweed    
       

Plume-like Inflorescence

  Bohemian knotweed    
       
Spade-shaped Leaf
  Bohemian knotweed    
       

Shallowly Heart-shaped Leaf

  Bohemian knotweed    
       
       

 

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