Japanese knotweed (Polygonum cuspidatum)
Description: Knotweed is an upright, shrub-like plant that dies back to the ground each year. Up to 10' high. The plant is aggressive and produces dense colonies from extensive rhizomes.
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: Alternately arranged on stem; typically grow to 4"-6" in length and 3"-4" in width, oval with a pointed tip.
Stems: The main stems are stout, upright, round in cross-section and hollow, resembling bamboo. The secondary stems are more delicate with a unique zig-zag pattern. As stems emerge from soil in spring they resemble pink and green spears of asparagus.
Flower: Many tiny white flowers arranged in spikes. Blooms in August and September.
Fruit: Small glossy winged fruits produce dark shiny seeds. Can be spread by wind, water, birds and insects. Not all seeds are fertile.
Root: Agressive, spreading rhizomes.
The problem is…an aggressive plant that forms dense colonies, excluding other plants. Knotweed is a threat to stream-side 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 cause cracks in concrete.
