Japanese Knotweed

Common name: Japanese Knotweed

Growth form: Large, herbaceous

Life Span: Perennial

Origin: Eastern Asia in Japan, China and Korea.

Flowering Dates: July-August

Reproduction: This species spreads by seed and by long, stout rhizomes. However, colonies rarely establish from seed. Primary spread of the species is reported to be through mechanical movement of plant parts.

Height: 6 to 12 ft.

Flower: are small , creamy white to greenish white, and grow in showy plume-like, branched clusters from leaf axils near the ends of the stems. Flower clusters are generally longer than the subtending leaf, unlike the shorter flower cluster found on giant knotweed and the midsize clusters found on the hybrid Bohemian knotweed. Leaf and flower characters are most reliable when looking near the middle of the branch.

Fruit: is 3-sided, black and shiny, approximately 1/8 inch long fruits are brown, shiny, triangular achenes

Seed: Knotweed can germinate from seed, although this is less common. Knotweed spreads when roots and stems are moved by waterways, floods or in contaminated soil. New plants quickly establish from the fragments.

Leaves: are thick and tough in texture, with short petioles, 2 to 7 inches long and about two-thirds as wide, spade shaped with a truncate base and an abruptly narrowed leaf tip. An identifying character is the lack of hairs on the leaf undersides. Instead of hairs, there are low, bump-like structures (scabers) visible on the veins with a hand lens.

Stems: are stout, cane-like, hollow between the nodes, (giving it the appearance of bamboo), The stem nodes are swollen and suronded by thin papery sheaths.

somewhat reddish-brown, 5 to 8 feet tall, and profusely branched. The plants die back above the ground at the end of the growing season.. However, the dead reddish brown canes often persist throughout the winter.

Underground: large underground network of roots (rhizomes).

Where Found: An escaped ornamental, Japanese knotweed is often found on disturbed soil, in waste places, neglected gardens, along roadsides, riverbanks and stream-banks and other moist areas in fields.

Uses and Values: The plant is sometimes grown as an ornamental. Flowers are valued by some beekeepers. Young stems are edible as a spring vegetable, similar to mild rhubarb. An excellent source of vitamin A, along with vitamin C and its cofactor, the antioxidant flavonoid rutin. It also provides potassium, phosphrous, zinc, and manganese. It is an excellen source of resveratrol, the same substance in the skin of grapes and in red wine that lowers LDL (bad) cholesterol and reduces the risk of heart attacks. Resveratrol may delay the onset of Alzheimers disease or slow its progression.

Poisoning: Caution should be used when consuming plant because it contains oxalic acid which may aggravate conditions such as rheumatism, arthritis, gout, kidney stones of hyperacidity.

Other: The species forms dense stands that crowd out all other vegetation, degrading native plant and animal habitat. In addition, Japanese knotweed can create a fire hazard in the dormant season. This perennial plant is difficult to control because it has extremely vigorous rhizomes that form a deep, dense mat. In addition, the plant can resprout from fragments; along streams, plant parts may fall into the water to create new infestations downstream.

Similar Species: Giant Knotweed (P.sachalinnse), Bohemian knotweed, (P. x bohemicum, a hybrid species) Himalayan knotweed (P. polystachyum) and cultivars including Pink Fleece Flower (Fallopia Japonica’Reynoutria), Varigated Fleece Flower (Fallopia Japonica, Variegata), Compacta, Crimson Beauty, Devon Cream, Milk Boy and others..