Invasive SpeciesJapanese knotweed

Fallopia japonica
FOUND by Fro-do
ID Confirmed
Quality checked by Komomo
Peer reviewed by Komomo
Field Notes
I am happy because I'm writing my research paper on this plant, and now I don't have to spend three hours looking for knotweed. Oh yeah, and for scientific discovery and that stuff. I smell dew and water, wet soil, and gas (the road I'm on is strangely busy). I hear cars driving by and birds chirping, and my mom telling me to stop taking pictures of grass and get in the car. I'm worried that this stand of knotweed might not be Fallopia japonica, but actually its hybrid plant, because those things are kinda scary. I'm also a little worried about being in a stream next to a power plant, but you know. I'd like to know if this really is japanese knotweed, and if I can expect it to grow more and overrun this place.
A sketch of our study site.
Supporting Evidence
Photo of my evidence.
Leaves of Fallopia japonica are green and very large, they can grow to be 18 cm long. They are heart-shaped with a flattened base, kind of like a shield. Okay, so they're shield-shaped. These leaves are obviously green, and they are large and shield-shaped.
Photo of my evidence.
Knotweed stems are hollow and green with reddish-purple spots all over. Since I don't think I can legally slaughter a stand of knotweed to prove it's hollow, I think I'll just stick to the colors. This stem is clearly green and covered in reddish-purple specks. It also looks kind of hollow, but I wouldn't know, because I'm a good citizen.
Photo of my evidence.
Back to the stems! Knotweed stems have several joints that are usually dark red, with a few branches always growing from them. This stem clearly has a red joint with adjoined branches.
Species Observation: Species Looked For
Did you find it?: 
I think I found it
Scientific name:
Fallopia japonica
Common name:
Japanese knotweed
Sampling method: 
Just looking around
Photo of our sampling method.
Place Studied
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Map this species
N 43.487117 °
W -70.472888 °
Observation Site Information
A photo of our study site.
Coastal - Beach or dune
Trip Information
May Street Power Plant Swamp
Trip date: 
Sun, 2013-05-26 16:30
Town or city: 
Type of investigation: 
Species Survey


Dear Fro-do,

Thank you for all that additional information! If you'd reported all that in your observation, I wouldn't have had a question. I'm glad I did ask because now we can all benefit from the extensive work you did!


The dangers of the hybrid... I just did a quick google search and did find some information. They have named the hybrid in Great Britain (Bohemian knotweed, or F. x bohemica), where all the Fallopia species are causing problems. Take a look here:

This page does report that the hybrid is a more aggressive spreader, at least in Great Britain, than the other Fallopia species.


thanks for the review. I made one for Purple Loosestrife too, you wouldn't mind reviewing that too would you?

I'm happy to take a look at it, but I'm no expert in purple loosestrife. I can't confirm your observation, if that's what you were hoping.

I'll take a look right now.


Hi Fro-do,

I loved reading your field notes and evidence statements! They are clear, engaging, interesting, and well written. Nice work.

And I share your concerns and curiosity about Fallopia japonica, and all Fallopia species. How much of the state could it cover? Who knows, which is why we need to keep watching it!

As to your identification... You definitely found a Fallopia species, you nicely documented several diagnostic characteristics (leaf shape, stems, joints). Most likely it is F. japonica, however, it could be the hybrid or F. sachalinensis.

Here's how you can tell: go back to the stand and take a close and careful look at the underside of the leaves. If there are little tiny hairs growing off the raised white veins on the underside of the leaf, it is likely Fallopia sachalinensis (giant knotweed) or the hybrid. If you can find no hairs, you are most likely right about it being F. japonica.

There is a species card for F. sachalinensis on

So, you're not quite done yet with your research. Hopefully your mom will take you back and be patient while you take once more picture of the underside of the leaf. You can use the link above to send the picture to us.

Thanks for your excellent work!


the stems are disimilar, there aren't red spots all over giant knotweed stems.
the way the branches grow are disimilar, giant knotweed doesn't have as many branches, and their joint are not dark red.
the leaves of giant knotweed are usually a minimum of 15cm, this leaf is barely past 12. at this time, the leaves would be at least 15 or 20 centimeters.
If this evidence doesn't convince you, I did check, there weren't hairs underneath, so you can just take my word for it.
Also, you wouldn't happen to know the dangers of the hybrid would you?