A relative of the more widely known Japanese knotweed (Fallopia japonica), Giant knotweed grows much taller, up to 4m high and has large (to > 30cm), heart-shaped leaves. Similar to Japanese knotweed, this plant produces woody, knotted, bamboo-like stems.
Leaves of Giant knotweed singly and shown side by with Bohemian knotweed, Japanese knotweed, Himalayan knotweed.
It is highly invasive, spreading from green plant fragments, rhizome or root fragments. Plants originating from buried fragments can grow through damaged walls and concrete.It is less widely distributed in Ireland than Japanese or Bohemian knotweed.
Originating from the Japanese island Sakhalin, it was first introduced as an ornamental garden plant but has thrived in the wild in Ireland and the UK. In spring it regenerates rapidly, as much as 7-10cm per day. In summer small clusters of flowers are produced, ranging in colour from creamy-white to greenish white. This highly aggressive invader breeds readily with Japanese knotweedand the hybrid is known as Bohemian knotweed (Fallopia japonicus x bohemica), also an invasive species.
Distribution of giant knotweed in Ireland
Data from Biodiversity Maps held by the National Biodiversity Data Centre www.biodiversityireland.ie 2011