Reynoutria japonica (Japanese Knotweed)

Plant Info
Also known as: Mexican Bamboo, Hancock's Curse
Family:Polygonaceae (Buckwheat)
Life cycle:perennial
  • Invasive - ERADICATE!
  • Noxious Weed
  • Prohibited or Restricted species
Habitat:part shade, sun; moist, disturbed soil, fields, along roads and railroads, gardens
Bloom season:August - September
Plant height:4 to 8 feet
Wetland Indicator Status:GP: FACU MW: FACU NCNE: FACU
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

Pick an image for a larger view. See the glossary for icon descriptions.

Detailed Information

Flower: Flower shape: 5-petals Cluster type: panicle

[photo of flowers] Branching spike-like or raceme-like clusters arising from leaf axils and at the tips of branching stems, with 3 to 6 flowers at each node. Flowers are 1/8 inch across with 5 white to greenish or pinkish petals. In the center is a bullet-shaped green ovary topped with a feathery 3-parted style and surrounded by 8 very short, white-tipped stamens, though the stamens are often sterile. Cupping the flower is a pale green to whitish calyx, tapering at the base to a slender stalk.

Leaves: Leaf attachment: alternate Leaf type: simple

[photo of leaves] Leaves are alternate, 4 to 6 inches (to 15 cm) long, 2 to 4½ inches wide, toothless, broadly egg-shaped to nearly round, abruptly narrowed to a pointed tip, straight across to broadly wedge-shaped or occasionally rounded at the base, on a stalk shorter than the blade. Surfaces are hairless; early leaves have minute, blunt hairs along major veins on the underside that can give it a rough texture, though these hairs do not persist.

[photo of a cluster of stems] Stems are hairless, hollow and bamboo-like, light green to blue-green often with red flecks or streaks, and usually clustered. Old stems may persist to the next season before disintegrating. Plants often form dense thickets from long, woody rhizomes.

Fruit: Fruit type: seed without plume

[photo of fruit] Fruit is a dry seed 2 to 4 mm long, shiny black-brown at maturity, with 3 broad, whitish wings, but seed production is usually poor, the plants primarily spreading by rhizomes.


Japanese Knotweed, also known by synonyms Fallopia japonica and Polygonum cuspidatum, is native to eastern Asia. It was introduced to the UK in 1825 by gardeners as an ornamental, brought to North America in the late 1800s, quickly escaped cultivation, and is now considered one of the top invasive species world-wide. Its tough rhizomes can break through concrete and it is incredibly difficult to eradicate, since root fragments can resprout. It is widespread in the eastern US and is likely now present in all of the lower 48 states. In Minnesota, it was available in the garden trade until 2014, when it was (finally!) designated a Prohibited Control Noxious weed.

Two other related species are also present in Minnesota: Giant Knotweed (Reynoutrias sachalinensis) and their offspring, the hybrid Bohemian Knotweed (Reynoutria × bohemica). Giant Knotweed is uncommon; there are currently no herbarium records for it and very few Minnesota records of it in other databases I've checked; it has quite large leaves (6 to 12+ inches long) with heart-shaped bases and young leaves have twisted, multicellular hairs along the veins. Bohemian Knotweed is more common, possibly more common than either parent, and is intermediate between the two, though it and Japanese Knotweed are frequently mistaken for each other.

There are hundreds of records on iNaturalist and EDDMapS for both Japanese and Bohemian Knotweeds, though the true abundance and distribution of either is murky and the images posted on those sites don't always show characteristics that could result in a positive ID. Thus the county distribution maps are incomplete to say the least. Multiple references note, in early growth, a difference in the hairs on new leaves, but we don't have the evidence to back up that claim. When flowers are present it is much easier: Japanese Knotweed flowers have very short stamens and Bohemian has comparatively long stamens. Late season plants lacking flowers should be distinguished by the leaves: the largest leaves of Japanese Knotweed don't exceed 6 inches (15 cm) long and leaf bases are mostly straight across to broadly wedge-shaped, where Bohemian leaves are distinctly longer than 6 inches and leaf bases are straight across to somewhat heart-shaped. But the bottom line is: both are invasive and should be eradicated.

If you have an invasive Knotweed on your property: the Minnesota DNR has more information, including control measures, that may be helpful. The best alternative for your landscape? The native Spikenard, Aralia racemosa!

About the genus Reynoutria: According to the Centre for Agriculture and Bioscience International (CABI), "Fallopia japonica was independently classified as Reynoutria japonica by Houttuyn in 1777 and as Polygonum cuspidatum by Siebold in 1846. It was not until the early part of the twentieth century that these were discovered to be the same plant (Bailey, 1990), which is generally referred to as Polygonum cuspidatum by Japanese and American authors but, following Meissner's 1856 classification, as Fallopia japonica in Europe (Bailey, 1990). Galasso et al. (2009) proposed transfer back to Reynoutria based on rbcL plastidial sequence analysis and Reynoutria japonica Houtt. is cited as the preferred name in The Plant List (2013)." The trend in databases such as iNaturalist and EDDMapS has been to revert to Reynoutria, and we have followed suit.

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More photos

Photos by K. Chayka taken in Ramsey and Washington counties. Photos by Peter M. Dziuk taken at various locations in Minnesota. Reynoutria japonica flowers by Paul Rothrock used under CC BY-NC 4.0 (cropped from original photo).


Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: Alissa - Coon Rapids, MN
on: 2011-05-13 13:32:07

This plant is taking over the yard on one side of my house! It's sprouting up through the grass, in the window wells, everywhere! My last two seasons of work to get rid of them has seemed to do nothing! Any suggestions? Thank you!

Posted by: Diana - NE Mpls
on: 2011-09-21 19:49:02

My yard - actually my neighbor's, but encroaching into mine. I understand ridding us both of this will be my new hobby.

Posted by: Cynthia - golden valley
on: 2012-04-20 13:29:34

i would like to grow this in pots (to keep it from spreading) due to its effectiveness in treating Lyme disease ("Healing Lyme" Stephen Harrod Buhner, 2005). Purchasing the herb is very expensive, and treatment often lasts longer than a year.

Posted by: K. Chayka
on: 2012-04-21 21:01:49

Cynthia, if you must have these plants, keep them in pots and keep them indoors.

Posted by: Annette - Falcon Heights MN
on: 2012-04-28 19:26:33

I have shoots. When I bought my house there was a huge forest of the stuff. Over the past two years I have cut it all down and and am still mowing some smaller shoots and applying roundup.

Posted by: Deb - Eden prairie
on: 2012-08-08 19:36:17

I have a spreading area of this. Thought it was a pretty plant and smelled good. Now I know what it is and have been trying to eradicate it. Last year I cut some at ground level and IMMEDIATELY doused with undiluted Super Concentrate Roundup using a sponge paint brush. I also sprayed the diluted mixture on new plants (less than 12" tall). The cut and douse method seemed to work well. That area has minimal regrowth. The sprayed plants have deformed, very small leaves, but they continue to grow, albeit slowly. Plans are to do more cut and douse. I was told to douse immediately after cutting as the plant seals itself quickly after bing cut. It's a slow process, but seems to work. It will probably be a yearly battle as with buckthorn for several years (have that to contend with also in the same manner.)

Posted by: joe - Taylors Falls
on: 2012-10-04 13:35:00

Actually I'm in Amery, Wi. just a few miles east of Taylors Falls. I'm interested in digging some roots. This is kind of urgent, as I have a friend with reacurring Lymes, and needs this soon. Thank You Joe

Posted by: K. Chayka
on: 2012-10-24 08:14:28

To anyone requesting or wanting to share information about Japanese knotweed and Lyme disease: Minnesota Wildflowers is not a forum for this issue. There are many other web sites devoted to Lyme disease and/or natural healing that would serve you better. Please use those resources instead. Thank you.
Katy Chayka, Minnesota Wildflowers

Posted by: Linda - Greenfield
on: 2012-11-28 00:55:56

I'm really sorry to see that you do not welcome inquiries regarding Japanese knotweed if we are interested in using it for natural medicinal purposes. I'm puzzled actually. I am interested in getting anyone's plant to grow in a pot inside year round. Please contact me if you are willing to help me. Thanks so much.

Posted by: K. Chayka
on: 2012-11-28 06:44:20

Linda, et al: Minnesota Wildflowers is just a field guide--we are all about plant identification and promoting natives in the landscape. Putting people in touch with each other regarding the procurement of invasive species, regardless of the reason, goes against the mission of Minnesota Wildflowers.

We are not experts on natural medicine or food value of wild plants, nor do we wish to become a clearinghouse for such things. There are numerous other venues with more information and authority than we can provide.

So I am sorry, but we cannot help you. Good luck in your quest.

Katy Chayka, Minnesota Wildflowers

Posted by: Connie - Minneapolis
on: 2014-05-31 19:21:13

A woman, who claimed to be a Master Gardener, was holding a plant sale in White Bear Lake. She sold me a plant she said was Bamboo. It turned out to be Japanese Knotweed. At first I thought it was so beautiful. But after it started spreading everywhere, I panicked. I ended up getting info from the horticulture dept. at UMN. I was told to spray the leaves with Round Up. I covered the plant, where I was able, with plastic bags and sprayed and sprayed. As it died, I went after the roots. I dug deep and far to get them out of there. I was afraid it was going to grow in the cracks of the sidewalks. Thankfully, I have gotten rid of it.

Posted by: Erica - Roseville
on: 2014-07-23 13:35:44

Japanese knotweed is growing in mass in several places along Victoria just south of County Road B in Roseville. (Ramsey county and Roseville have been alerted, but private landowners in the area may want to know)

Posted by: Andy - On Co Rd 27 SW near Crooked Lake in Falwell
on: 2014-09-17 10:01:41

Large flowering stand seen flanking the driveway of a private residence, near the public landing for Lobster Lake.

Posted by: Nicole - Hastings
on: 2015-05-12 09:49:56

We've read that in the UK, that Japanese Knotweed plants were actually coming through the foundations of houses and growing. Is there worry of this happening with the growth of these plants here in Minnesota?

Posted by: K. Chayka
on: 2015-05-12 20:04:33

Yes, Nicole, Japanese knotweed can crack foundations here as well.

Posted by: Carole - Shoreview
on: 2015-09-21 10:57:53

I was contacted by a Shoreview city volunteer group, replanting a boulevard, wanting id and removal advice. Their plant was the dwarf pink. I asked for but have not received an exact location yet. BTW; EDDMapS now lists this plant as Reynoutria japonica Sieb. & Zucc.

Posted by: K. Chayka
on: 2015-09-23 17:19:34

Flora of North America still lists it as Fallopia japonica, with Reynoutria japonica Houttuyn a synonym.

Posted by: Teri - Robbinsdale
on: 2016-08-12 11:46:13

There is a large bank of Japanese Knotweed along the channel coming out of Twin Lake, where there is a footbridge crossing near 46th Ave, 2 blocks west of France Ave.

Posted by: Lynn - Lake Elmo
on: 2017-01-27 14:35:31

My neighbor brought it back from Wisconsin and planted between our yards in terraces. I've been trying to remove. It's very difficult.

Posted by: Tom W - Mendota Heights
on: 2017-06-28 15:52:58

My fathers backyard has been overtaken by this stuff.

Posted by: Erica T - Roseville
on: 2017-07-20 13:37:55

Roseville has been battling this for a few years now, and I've heard Stillwater as well. A huge hedge was treated along Victoria near Reservoir woods. It required multiple treatments to remove many plants near the wetlands but the plant came back in full force on private properties in the area that were only treated once. I now see small plants popping up on residential properties between Victoria and Dale (south of County Road B). Just a note to the herbalists.... When it is farmed for food or root derivatives in its native country, they use bulldozers to get the roots which can span up to 60 or so feet. Even though it might be used for nutraceutical production, it easily escapes cultivation (so recommend letting those from country of origin do the farming).

Posted by: Patti Flynn Heimsness - Austin - Stewartville
on: 2018-08-18 19:04:00

I drive I90 weekly and I am seeing an alarming amount of Fallopia japonica var. japonica (Japanese Knotweed)(?)on the plantings in the ditches. It is so pervasive - it cannot be good. I hope someone can check on this for Mower County. The plant has a lovely (deceptive) white flower. I think we may have the Zebra Mussel of weeds here. Thank you.

Posted by: Z. Benson - Anoka County, Ramsey County
on: 2018-12-16 20:50:40

I have spotted a patch growing under a powerline between a road and a bike trail in Lino Lakes, about a mile north of the Anoka/Ramsey County line. I also spotted a patch somewhere in Circle Pines.

Posted by: magali disdier - Spring Valley
on: 2021-03-20 21:09:09

i have that plant in a corner of my yard, under the tress. I pulled out as much as I could, then covered with landscape thick black plastic. then I planted hostas in holes I made in the plastic. I haven't completely eradicated it , especially that my neighbors don't do anything about it. But the clump is lot less.

Posted by: Darrick P Wotachek - Cambridge
on: 2022-01-03 14:36:03

To Nicole from Hastings & others: I have witnessed a landowner have it grow through his foundation in his garage in a city in my jurisdiction. Another landowner on Long Lake has it growing on their septic system I am working with them to get it eradicated before it causes structural damages. In the UK they are spending thousands/millions of dollars trying to eradicate it from what I have read. MDA is regulating it on the Mandated Control List for these reasons and others. Takes 3-5 years to fully get rid of it when it escapes captivity due to the rhizome reserves. My goal is to keep it out of the Wild and Scenic Rum River Valley. Respectfully. Isanti County Agricultural Inspector.

Posted by: Susan M - NE Minnesota-Canada border
on: 2023-02-04 20:58:04

I'm often asked about a plant growing near a deck at our business and finally decided to figure out its name. After research, I'm certain it's compact Japanese knotweed. I gather it's not as invasive and indeed, in the 15 years I've known of this plant it has spread an additional 4 feet in the garden, but not outside the garden boundaries. We have a short summer here, so it doesn't get much growing time before it's killed back. Now I'm wondering if it's ok to leave it. We are on public lands in a national forest. I've never seen it growing anywhere else but this one spot, but is it irresponsible to let it be?

Posted by: K Chayka
on: 2023-02-05 10:02:28

Susan, public land in a national forest is no place for something like this. There is zero benefit in keeping it around. Any aesthetic value to humans just not justify its continued existence.

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