The New Zealand Plant Conservation Network

Species

Fallopia japonica

Etymology

japonica: of Japan

Common Name(s)

Japanese knotweed

Family

Polygonaceae

Flora Category

Vascular - Exotic

Structural Class

Dicotyledonous Herbs other than Composites

Synonyms

Reynoutria japonica, Polygonum cuspidatum

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

This page last updated on 24 Feb 2013