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Family Name:        Polygonaceae  =  Knotweed or Buckwheat  Family
Scientific Name: previous scientific namePolygonum  cuspidatum  next scientific name      plant name pronunciation
Common Name:   Japanese Knotweed, Mexican Bamboo
1  Polygcusp_AAA03_May5
2  Polygcusp_AF01
3  Polygcusp_AF02_Aug20
4  Polygcusp_DS09_Aug20
5  Polygcusp_LF03_Aug20
6  Polygcusp_LF08_Aug20
7  Polygcusp_OF03_Sep24
8  Polygcusp_OF07_Aug20
9  Polygcuspcomp_AF01
10  PolygcuspComp_AF03
11  Polygcuspcomp_OF01b
12  PolygcuspComp_OF03
13  PolygcuspCrimsonBeauty_DS
14  PolygcuspCrimsonBeauty_DS
15  PolygcuspCrimsonBeauty_DS
16  PolygcuspCrimsonBeauty_LF

Picture Notes:  Pictures 9 to 11 are Polygonum cuspidatum var. compactum.
Pictures 12 to 15 are Polygonum cuspidatum cv. Crimson Beauty.

More Information:                                

Distribution:  Japan; species often becomes weedy.

Synonyms:  RHS uses *Polygonum japonicum for Polygonum cuspidatum. Polygonum cuspidatum is sometimes listed as * Fallopia japonica (in Flora of North America), Polygonum reynoutria, or Reynoutria japonica.

Hardiness Zone:  USDA Zones 5-9       (view USDA zone map)

Size:   3-8 ft. by 4 ft.

Form:   Herbaceous rhizomatous perennial.


Stem/Bud:   Stems are mottled red-brown, erect, angled, hollow and outward curved. Leaves are swollen at nodes, stout, leafy, branched, and bamboo-like.

Leaves:   Leaves are round or ovate, pointed, alternate, simple and 4-6 in. long with 1 in. long petioles. Leaves have paired stipules (basal leaf appendages) of cylindrical sheaths (ocreae) positioned above the swollen stem nodes.

Fall Color:   

Flower:   Flowers are green-white, small (1/8 in. long), 5-sepaled, lacking petals and loosely clustered on 2-3 in. long, axillary spikes. Flowers July to October.

Fruit:   Fruit are small, 3-sided, smooth, black achenes.

Uses:   Found in waste places and on roadsides. Can be used as hedges or screens in a large garden. Species can become invasive and difficult to eradicate. Often mistaken as bamboo. The cultivars are not imvasive.


Culture:   Grow in full sun to part-shade in moist, average soil.


Notes:    RHS uses *Polygonum japonicum. Sometimes listed as Fallopia japonica (FNA), Polygonum reynoutria, or Reynoutria japonica. Species ia a very aggressive weed, especially near water. Thrives in alleys and on roadsides, etc., often reaching the size of a lilac hedge.

Notes 2:   Introduced in Michigan. Weedy.

Notes 3:   


                 var. compactum  =   Dwarf Japanese Knotweed, Dwarf Mexican Bamboo
                        ( RHS uses *Polygonum japonicum var. compactum. Sometimes listed as
                         Polygonum reynoutria, or Reynoutria japonica var. compacta. )
                                 [ RHS uses Polygonum japonicum var. compactum. Sometimes
                                  listed as Polygonum reynoutria or Reynoutria japonica var.
                                  compacta. Grows only 12 to 18 in. tall. ]

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