Picture Notes: Pictures 9 to 11 are Polygonum cuspidatum var. compactum.
Pictures 12 to 15 are Polygonum cuspidatum cv. Crimson Beauty.
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.
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.
= 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.
listed as Polygonum reynoutria or Reynoutria japonica var.
Grows only 12 to 18 in. tall.
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