giant knotweed (Fallopia sachalinensis)
A knotweed native to Japan and the island of Sakhalin, introduced in the 19thC. It is now an alien invasive species, widespread in Britain but less common and less aggressive than its close relative Japanese knotweed. It is found mainly on river banks, lake shores and other moist sites, and on disturbed ground. It grows up to 5m tall and its leaves are up to 40cm long.