2021 Margot Cunningham 2019 John Malpas 2019 John Malpas 2018 David Greenberger 2021 William Miller 2018 Rachel Kesel 2005 Louis-M. Landry 2019 David Greenberger 2018 John Malpas 2018 Chris Qian 2011 Louis-M. Landry
Fallopia japonica is a perennial herb that is not native to California.
[www.invasive.org] Background, Distribution & Habitat, Ecological Threat: Background
Japanese knotweed was probably introduced into the United States in the late 1800s. First used as an ornamental plant, it has also been planted for erosion control and landscape screening. It is designated a noxious weed in the state of Washington.
Distribution and Habitat
Japanese knotweed occurs across the U.S. and has been reported to be invasive in natural areas throughout the northeast into Georgia and west to Missouri, with additional infestations in Oregon and Washington. It can tolerate a wide variety of challenging conditions, including deep shade, high salinity, high heat, and drought. Knotweed is commonly found near water sources, such as along streams and rivers, and in a variety of low-lying areas like ditches, waste places, utility rights-of-way and around old home sites.
It spreads quickly to form dense thickets and pushes out native plant species. Knotweed poses a significant threat to riparian areas where it can survive flooding events and rapidly colonize scoured shores and islands. Once established, populations are extremely persistent. (contributed by Mary Ann Machi)
[Wikipedia] Japan, China, Korea native: Reynoutria japonica, synonyms Fallopia japonica and Polygonum cuspidatum, is a species of herbaceous perennial plant in the knotweed and buckwheat family Polygonaceae. Common names include Japanese knotweed and Asian knotweed. It is native to East Asia in Japan, China and Korea. In North America and Europe, the species has successfully established itself in numerous habitats, and is classified as a pest and invasive species in several countries. (contributed by Mary Ann Machi)
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Information on California plants for education, research and conservation,
with data contributed by
public and private institutions and individuals.
[web application]. 2023. Berkeley, California:The Calflora Database
[a non-profit organization].Available: