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 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, oval with a pointed tip.
Stems: The main stems are stout, upright, round, and hollow; resemble bamboo. The secondary 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. 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: Agressive, spreading rhizomes.
The problem is…an aggressive grower that forms dense colonies, excluding other plants. Widespread rhizomes form dense undergrowth. 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 cracks in concrete.
