Flora of New Zealand Series

giant knotweed

Giant rhizomatous herb forming large thickets; stems glabrous, green, 2-4 m high, c. 2 cm diam., woody at base. Petiole 2-6 cm long, often reddish, channelled above, with 3 pits at base on dorsal side except in some infl. lvs. Lamina 10-30-(40) × 5-22-(30) cm, broad- to oblong-ovate, glaucescent below, entire to somewhat undulate, usually glabrous when mature, or sometimes puberulent towards base of veins on upper side, with > 14 pairs of lateral veins; base shallow- to deep-cordate; sinus wide; apex acute to cuspidate. Ochreae to 6 cm long, glabrous, soon deciduous. Panicle branches solitary or fascicled, at least the lower branches < or = petioles, erect to spreading, densely puberulent. Bracts small, ± puberulent, acuminate or long-cuspidate. Pedicels 0.5-3 mm long, glabrous, jointed in lower 1/2. Perianth 1-2 mm long at anthesis (excluding basal decurrent wing), white or greenish white; segments broad- or oblong-obovate, keeled. Filaments to c. 1.5 mm long. Stigmas fimbriate. Fr. valves prominently winged. Nut not seen.

N.: from New Plymouth southwards; S.: commonest in Westland, but also in drier areas such as Motueka (Nelson Province) and Christchurch and Hororata (Canterbury).

E. Asia, N. Japan 1935

Very sporadic cultivation escape, usually on roadsides in the vicinity of habitations and forming very conspicuous giant clumps.

FL Nov-Apr.

R. sachalinensis is sometimes confused with R. japonica, although the characters given in the key adequately distinguish them; in addition, R.sachalinensis does not produce mature fr. in N.Z. It has previously been recorded in N.Z. as Polygonum sachalinense.