Japanese knotweed (Fallopia japonica) is a fast growing, invasive perennial with a terrible reputation for spreading and excluding other native plants. Its roots are also capable of breaking through concrete and other man-made materials (1).
But it’s not all bad! It looks quite nice when it is flower, right now in September, and it’s good for bees and insects. Another blogger beat me to the excellent title ‘knotty but nice’ (2) and there is a lot out there on the Web on it’s good-for-beeness!
There seems to be some debate on bee fora (forums) about the tastiness of Knotweed honey, which is sometimes sold as ‘bamboo honey’ in the US apparently. I’d like to try it; bet it’s nice.