Japanese knotweed

Fallopia japonica
Seed set less likely in Australia but hybridizes readily with F. sacchalinenis; hybrid is known as F. x bohemica
Family: Polygonaceae
Origin: East Asia (Korea,Taiwan and eastern China) and Japan
Habit: Large herbaceous perennial 1.5–3 m high, forming a dense thicket. Hollow stems with raised nodes bamboo-like in appearance, often glaucous and red-brown, numerous and branched above, dying back in winter
Leaves: Leaves broad-ovate with margin entire, 5–15 cm long, 2–12 cm wide, apex long-acuminate to cuspidate, base truncate
Flowers: Small cream or white clusters in erect racemes 6-15 cm long in late Summer and Autumn
Fruit and Seeds: Three angled papery sheath covers seed 2-4 mm long, glossy dark brown to blackish
Roots: Invasive rhizomatous root system that can extend 7 metres horizontally and 3 metres deep; can crowd out any other herbaceous species
Dispersal: Landfill; vegetative fragments spread by water, reasonably strong wind and earthmoving activities
Control: As reproduction almost entirely by extensive rhizome system capable of germination from minute fragments makes removal by excavation difficult; sprouts vigorously from cut roots. Integrated management according to infestation size and situation recommended e.g. smothering/suppression from photosynthesis, herbicide applied close to flowering in late Summer or Autumn. .
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