Fallopia japonica
NPPA pest plant
Environmental Weed (2024)
Common names
Japanese knotweed, Asiatic knotweed
Biostatus
Exotic
Category
Vascular
Structural class
Herbs - Dicotyledons other than Composites
Flower colours
White
Detailed description
Rhizomatous herb forming large clumps; stems usu. 1~2m tall, approx. 1.5cm diam. at the woody base, generally zig-zagging, glabrous, glaucous to reddish. Petiole 1~5.5 cm long, mostly dark crimson, channelled above, with a single pit at base on dorsal side. Lamina 8~23 x 5~17cm (infl. leaves often smaller and more elongated), broad-ovate, glaucescent below, with < 14 pairs of lateral veins, often minutely puberulent on veins near base above, otherwise glabrous, undulate; base usu. truncate, sometimes shallowly subcordate, esp. on vegetative shoots; apex cuspidate. Ochreae to around 3cm long, deciduous, glabrous. Panicles with branches clustered to 6cm long, > petioles, erect or suberect, densely puberulent. Bracts small, glabrous or puberulent, cuspidate or cuspidate-acuminate. Pedicels > bracts, glabrous, jointed in lower half. Perianth 1.5~2.5mm long at antithesis (excl. decurrent base), white; segments obovate to oblong-obovate, keeled. Filaments to 2mm long. Stigmas fimbriate. Valves of fruit 7~11mm long (incl. broad wing); apex notched. Nut 2.5~3mm long, obtusely angled, glossy brown. (-Webb et. al., 1988)
Habitat
Terrestrial.
Conservation status
Not applicable
Detailed taxonomy
Family
Synonyms
Reynoutria japonica, Polygonum cuspidatum
Ecology
Flowering
December, January, February, March
Year naturalised
1935
Origin
Japan
Reason for introduction
Ornamental
Life cycle and dispersal
Perennial.
Other information
Etymology
japonica: Of Japan
National Pest Plant Accord species
This plant is listed in the 2020 National Pest Plant Accord. The National Pest Plant Accord (NPPA) is an agreement to prevent the sale and/or distribution of specified pest plants where either formal or casual horticultural trade is the most significant way of spreading the plant in New Zealand. For up to date information and an electronic copy of the 2020 Pest Plant Accord manual (including plant information and images) visit the MPI website.
Environmental Weed (2024)
This plant is named in a list of 386 environmental weeds in New Zealand 2024 prepared by DOC. 759 candidate species were considered for inclusion on this new comprehensive list of environmental weeds in New Zealand. The species considered were drawn from published lists of weed species, lists of plants that must be reported or managed by law if observed, existing national and regional programmes and agreements for pest management, and species already managed by the Department of Conservation (DOC). Candidate species were then assessed to see if they were fully naturalised and whether they have more than minor impacts in natural ecosystems. Read the full report here.