Japanese Knotweed (Fallopia japonica) Japanese Knotweed facts: Arrived in UK (South Wales) late 19th century. 2 – 3m height but spreads 7m horizontally. Perennial Rhizome. Edible (the early shoots!). Female only in UK but can Hybridise with Himalayan Knotweed. Can be spread via small cut pieces. Estimated to cost £1.56 billion to eradicate in UK (2007). Significant issue for developers (eg Olympic grounds). Can be sprayed with round up but can prove resistant. Can hybridise with Himalayan Knotweed which has male flowers. For more information on Japanese Knotweed, especially with regards homes and developments, please see here.