B&M - green caterpillar

A bright lime green caterpillar, on the leaf it was crawling under / over.
[not hairy and quite active, was about 30 - 35m long, at a guess ?]

Whatever the plant is [?] - I was cutting it out from in & behind one of my rosa rugosa bushes, when I found this caterpillar ... after photographing it, I found another example of said weed to put it onto ...