Elsewhere, I have nicknamed Japanese knotweed the "Godzilla weed." That's because this noxious weed (Polygonum cuspidatum) is the most difficult invasive plant to eradicate that you are ever likely to encounter! More typical nicknames you'll find for this plant are "Mexican bamboo" and "Japanese bamboo."
The picture here shows what the new shoots look like. When its "bamboo shoots" first appear in spring, they can be considered edible weeds. I would be very cautious, though, in harvesting this plant for eating -- no matter how tender and nutritious the new shoots are supposed to be. The reason for my caution? Well, because this noxious weed is so difficult to get rid of, people have thrown everything but the kitchen sink at it over the years, in attempts to eliminate it. That includes toxic substances. So unless you are very familiar with the ground where a potential crop of Japanese knotweed is growing, I would err on the side of safety and refrain from harvesting it for culinary purposes.
The tender Japanese bamboo shoots eventually harden as they grow taller, then die in winter, becoming brittle canes (the root system lives on underground, unfortunately). Even as new shoots in spring, though, they have the strength of Godzilla: many a time I have seen them exploiting cracks in concrete in urban areas to push there way up through sidewalks, driveways or paved parking lots.