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Ironic, isn't it, that the leaves are shaped something like those shovels they use for grave-digging, in horror movies?
(truncate, that is)
There was an outbreak of it locally a couple of years ago, and I had to be "very firm" with the council to get them to kill it.
How to take close-ups with cheap phone and hand-lens:
Field Guides for Budding Botanists:
There is a good description of the differences between japonica and bohemica in Watsonia
Another clue to its ID are the healthy looking anthers in these pictures. Most japonica in Europe is a male sterile clone.
Also good pictures at http://alienplantsbelgium.be/content/reynoutria-x-bohemica
Interesting, thanks. I should have taken a picture of the leaf underside. It is hard to know what will be important until after the event. I have made a note to check later in the year.
Lat/Lng: 45.822083, 8.440702