Photo credit: © Stoun Swon/Flickr
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Species at a Glance
Giant knotweed is an herbaceous perennial and member of the buckwheat family. It forms large colonies of erect stems which are woody in appearance and can reach heights over 3.7 m (12 ft).
Leaves: Large rounded leaves alternate on the stem and reach over 0.3 m (1 ft) in length. They have heart-shaped bases and rounded lobes. Thin wavy hairs are present on the underside of the leaves in June through mid-September.
Flowers: Small flowers reach about 10 cm (3.9 in) in length and range in color from a creamy white to greenish-white. They grow in short branched clusters from leaf axils at the ends of stems and appear from August to October.
Fruits/Seeds: Three-sided seeds are shiny, brown to black, egg-shaped, and have a paper-like texture.
Stems/Roots: Smooth, hollow, jointed stems are swollen at the nodes, light green in color, and resemble bamboo shoots.
Giant knotweed looks similar to the other knotweed species, including Japanese knotweed (Fallopia japonica) and Virginia knotweed (Persicaria virginiana). Giant knotweed is generally much larger and can be distinguished by its heart-shaped leaf bases and the fine hairs on the undersides of the leaves.
Giant knotweed grows in various levels of sunlight in moist soils of streams, riverbanks, wet meadows, roadsides, and areas of human disturbance.
Giant knotweed spreads primarily through rhizomes and root fragments that disburse to new areas by natural means such as wind and water, and by man-made disturbances such as roadside clearings and equipment
Native to the Sakhalin Islands of Japan, giant knotweed was introduced to the United States around 1900 as an ornamental. It is currently widespread across the United States and is found in all Mid-Atlantic states except South Carolina.
Note: Distribution data for this species may have changed since the publication of the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016), the source of information for this description.
Once established, giant knotweed is very difficult to eradicate. It quickly forms dense stands that crowd out native vegetation, clog waterways, and displace streamside vegetation, causing erosion along stream banks and degrading fish and wildlife habitat.
Information for this species profile comes from the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016).