Zig-zag stem, shield shaped leaf with flat base. Some hybrid forms have heart-shaped base.
Bamboo-like canes with purple/red speckles
Lacey white flowers that appear between August and September in Michigan.
Japanese knotweed and Giant knotweed can hybridize and form Bohemian knotweed, which inherits traits from both parents. Unfortunately, it's being reported that Bohemian knotweed inherits some of the WORST traits making it a more formidable foe. Only trained personnel can tell a difference between species of knotweed, so this information is a general overview of knotweed.
Midwest Invasive Species Information Network (MISIN) Training modules: