Japanese knotweed (Polygonum cuspidatum)
Description: Knotweed is an upright, shrub-like, herbaceous plant that can grow up to 10' high. The plant is aggressive and produces extensive rhizomes in dense clumps.
Life cycle: Perennial
Habitat: Grows best in full sun and can grow semi-shade. It is found along roadsides, stream and river banks, wetlands, wet depressions and woodland edges. It can tolerate a wide array of soil and moisture conditions.
Leaves: Alternating and broad. They typically grow to 4"-6" in length and 3"-4" in width with an abrupt pointed tip.
Stems: Upright, round, and hollow. Resemble bamboo.
Flower: Many white flowers arranged in spikes. Bloom in August and September.
Fruit: Small glossy winged fruits the produce dark shiny seeds. Can be spread by wind, water, birds and insects. Not all seeds are fertile.
Root: Rhizomes
The problem is…an aggressive grower. Widespread rhizomes form dense undergrowth. Knotweed is a threat to riparian areas because small pieces of rhizome washed downstream can start new colonies. Knotweed can contribute to both stream and bank erosion and flooding. Its rhizomes and shoots can penetrate asphalt and cracks in concrete.
