Fallopia japonica
Common name
Japanese knotweed
Synonyms
Reynoutria japonica, Polygonum cuspidatum
Family
Polygonaceae
Flora category
Vascular – Exotic
Structural class
Herbs - Dicotyledons other than Composites
Conservation status
Not applicable
Habitat
Terrestrial.
Features
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)
Flowering
December, January, February, March
Flower colours
White
Year naturalised
1935
Origin
Japan
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.
Reason For Introduction
Ornamental
Life Cycle Comments
Perennial.