T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network

Fallopia sachalinensis (Giant knotweed)

Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Core eudicots
Order: Caryophyllales
Family: Polygonaceae
Genus: Fallopia
Species: F. sachalinensis
Binomial name: Fallopia sachalinensis
Synonyms: Polygonum sachalinense, Reynoutria sachalinensis, Reynoutria brachyphylla, Tiniaria sachalinensis
Common name: Giant Knotweed, Sakhalin knotweed

Fallopia sachalinensis a large, upright, herbaceous plant or shrub native to north-eastern Asia, northern Japan and the far east of Russia. It was brought to New Zealand as a garden plant by has now escaped to the wild and is now as an invasive species forming large clonal colonies. It is similar to Fallopia japonica (Japanese knotweed) but is larger, growing over 4m high and having leaves around 20-40cm. 
Fallopia sachalinensis also has flowers that are greener in colour and leaves that are more rounded at the base than Japanese knotweed and have scattered hairs on the undersides. It is found growing along roadsides and on wasteland.

Fallopia sachalinensis has smooth, hollow stems have prominent, swollen joints that give them a slightly bamboo-like appearance.
The alternately arranged leaves are very large, heart-shaped and are >40 cm long and > 20 cm wide and have a somewhat wavy, crenate margin. Where the leaf stalk meets the stem there is a membranous, sheath-like, structure.
The small whitish or greenish flowers are borne in late summer or early autumn on short dense panicles up to 10 cm long. The male and female flowers are often produced on separate plants.
The seeds which are a blackish or a dark brown in colour (>4 mm long) are enclosed in a three-winged fruit (>15 mm long).
Fallopia sachalinensis has strong, extensively creeping, spreading rhizomes which form large colonies. A significant proportion of the biomass of Fallopia sachalinensis is below ground. The roots can extend deep into the ground forming a deep mat that can be more than 2 m deep and >20 m long.

There is also a hybrid between Japanese Knotweed and Giant Knotweed called Fallopia x bohemica. This hybrid is particularly worrying as it may be capable of producing viable seed. Stands grow to 2.5 - 4 metres. Leaves are intermediate between Japanese and Giant Knotweed and have scattered stiff hairs on the undersides.

The short dense panicles of flowers

A spouting rhizome.

 Thanks to Wikipedia for text and information: https://creativecommons.org/licenses/by-sa/3.0/