Giant knotweed
Reynoutria sachalinensis · Aquatic plants
Whole plant · Photo: CC0
Also called Sakhalin knotweed, Polygonum sachalinense, Fallopia sachalinensis
State noxious weed listing
- Idaho: Control
- Oregon: B list
How to identify Giant knotweed
- Hollow, bamboolike canes 10 to 16 feet
- Very large leaves 8 to 16 inches with a deep heart shaped base
- Long, wavy hairs on the leaf underside
- Greenish white flower clusters shorter than the leaves
Similar plants
Japanese knotweed has smaller leaves with a squared off base; Bohemian knotweed is in between with short stiff hairs under the leaves.
Growth profile
| Growing season | Shoots come up in spring, flower in late summer and die back at frost. |
|---|---|
| Starts growing | Spring |
| Light | Full sun to part shade |
| Depth | Moist banks above the waterline |
| How it spreads | Rhizomes and stem fragments |
| Habitat | Streambanks, pond edges, ditches and old garden sites. |
Why it matters in a lake
The largest of the knotweeds, with the same deep rhizomes and control challenges as Japanese knotweed.
Where it is found
- Idaho: Rare
- Oregon: Occasional
- Wyoming: Not recorded
Classification
| Kingdom | Plantae |
|---|---|
| Phylum | Tracheophyta |
| Class | Magnoliopsida |
| Order | Caryophyllales |
| Family | Polygonaceae |
| Scientific name | Reynoutria sachalinensis |
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