Appearance ²

It is an annual herb with hollow, light-green stems that resemble bamboo. Early in the growing season, the new shoots can grow three to four inches a day. The plants have greenish-white flowers that appear from August to October.

Introduction ²

It was introduced in the late 1800’s, and it was native to Asia. It was introduced as an ornamental.

Similar Native Species ²

Giant knotweed (Fallopia sachalinensis) is larger than Japanese knotweed, often reaching 4m (13 ft) in height. It can be distinguished by its larger leaves and heart-shaped leaf bases. They taper towards their tips, rather than being abruptly pointed. Giant knotweed leaves have long, wavy hairs on their undersides, while the hairs on Japanese knotweed are reduced to barely visible bumps.
Giant knotweed and Japanese knotweed hybridize to form Bohemian knotweed (Fallopia Xbohemicum). The hybrids are fertile and back-cross readily, yielding a continuous range of variation between the characteristics of their parent species, including size, leaf bases and tips. The hairs on the leaf undersides are short with broad bases.
The related non-native Himalyan knotweed (F. polystachyum) has narrower, sharply-pointed lance-shaped leaves that are up to 20 cm (8 in) long. Its leaf bases may be tapered or slightly heartshaped. It can grow up to 1.8 m (6 ft) tall.

Impacts on Ecosystem ²

It is known to crowd out native species because it quickly produces dense stands that can clog waterways and displace other vegetation.

Citations ²

http://www.invasivespeciesinfo.gov/plants/knotweed.shtml
http://www.dcnr.state.pa.us/cs/groups/public/documents/document/dcnr_010254.pdf
http://mnfi.anr.msu.edu/invasive-species/JapaneseKnotweedBCP.pdf

Sources and Credits

1. (c) Marie Studer, some rights reserved (CC BY), uploaded by Marie Studer
2. (c) gburg2016, some rights reserved (CC BY-SA)

More Info

• iNat taxon page
• Biodiversity Heritage Library
• BOLD Systems BIN search
• eFloras.org
• Global Biodiversity Information Facility (GBIF)
• HOSTS - a Database of the World's Lepidopteran Hostplants
• IPNI (with links to POWO, WFO, and BHL)
• Maryland Biodiversity Project
• NBN Atlas
• SEINet Symbiota portals
• Tropicos
• World Flora Online

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