Japanese knotweed
Reynoutria japonica Houtt.
- light
- Full sun
- water
- Medium
- tall
- 3.5 m
- wide
- 3.5 m
Polygonaceae
Also called Asiatic Knotweed, Japanese fleece flower, Donkey rhubarb, Itadori knotweed, Japanese Knotweed
Formerly Fallopia japonica, Pleuropterus cuspidatus, Pleuropterus zuccarinii, Polygonum cuspidatum, and 11 more
When it flowers
Not known yet in the tropics: too few flowering observations to read a season from.
Read from iNaturalist photographs of it in flower. A month counts at 50% of the best month's flowering share (smoothed over three months) and 10% of its flowering count, from at least 100 flowering observations in the band.
If a child, a pet or anyone may have eaten a plant, contact a doctor or vet straight away, or call the National Poisons Information Centre (AIIMS, New Delhi) on 1800 116 117, free and open 24 hours.
Something wrong with it?About it
- Grows as
- Perennial or rhizomatous geophyteKew's checklist, not yet checked
- Climate
- TemperateKew's checklist, not yet checked
- Wild in
- Russian Far East to China and Temp. E. AsiaKew's checklist, not yet checked
- Light
- Full sun (6 h or more)Read from NC State Extension, one source
- Height
- 3.0 m to 4.0 mRead from NC State Extension, one source
- Spread
- 91 cm to 6.1 mRead from NC State Extension, one source
- Water
- Average: moist, well drainedRead from NC State Extension, one source
- Flowers
- White, cream, greenRead from NC State Extension, one source
Not known yet: coldest it survives, heat, hottest it survives.
In other languages (12)
- Polish
- rdestowiec ostrokończysty
- Chinese
- 虎杖, 虎杖叶, 贯脚
- root
- FALJAP, Glúineach bhiorach, Canclwm Japan
- Norwegian Bokmål
- parkslirekne
- Portuguese
- Sanguinária-do-japão
- Japanese
- イタドリ, メイゲツソウ, ケイタドリ
- Dutch
- Japanse duizendknoop, Compacte Duizendknoop
- Finnish
- japanintatar, neidontatar
- French
- Renouée du Japon
- Czech
- křídlatka japonská
- Hungarian
- Ártéri japánkeserűfű, japán óriáskeserűfű
- Slovenian
- Japonski dresnik, japonski dresnik
Where this comes from
- iNaturalist, read 2026-10-25, CC0-1.0 (observation counts)
- Wikidata, read 2026-10-25, CC0-1.0
- Kew's checklist, read 2026-10-24, CC-BY-4.0
- NC State Extension, read 2026-10-25, fact, cited
- Wikimedia Commons, read 2026-10-25, CC0
- iNaturalist, read 2026-10-25, CC BY-SA
- iNaturalist, read 2026-10-25, CC BY
- iNaturalist, read 2026-10-25, CC BY
- 3D model: Reynoutria japonica (built for Vanagrha) by Vanagrha, own
A fact “checked by a majority of its sources” was settled by a vote of the pages it was read from, not by a person reading it; one marked “one source” rests on that page alone. Anything else not marked checked has not been checked yet. Where nothing is known, the page says so rather than guess.