Japanese knotweed
Japanese Knotweed (Fallopia japonica) has a stem similar to bamboo, which is covered in purple speckles and triangle-like green leaves with a length of 10-15cm. The roots form an extensive system, that can penetrate up to 3m in depth, and up to 7m laterally; this makes it very difficult to remove.
It was first introduced to Europe from Asia in the mid 1800s, and was first recorded in the wild in the UK in Wales in 1886. It was introduced as an ornamental plant, and was grown in gardens and parks before it began to spread. It was also planted along pathways and embankments, as it was thought to protect the ground against landslips.
Japanese Knotweed grows best on disturbed ground; and is commonly found on riverbanks, railways, the sides of roads, and in urban areas. It can also be found in woodlands.
Find some more information on Japanese knotweed here.