Knotweed complex

Polygonum spp.

Family: Polygonaceae

Description and Life Cycle

As with most weeds, knotweeds’ spread is due mainly to human activity. Knotweeds can produce viable seed, but the primary means of spread is by their roots. Rhizomatous roots may extend from the parent plant up to 7 m laterally and to a depth of 2 m. Grubbing, chopping or cultivation of the roots encourages spread. Plants can sprout from root pieces buried up to 1 m deep and growing shoots have been known to penetrate asphalt 5 cm thick.

Also, stem pieces as small as 0.7 gram in soil or water can produce viable plants in 6 days. Once established, young shoots sprout in March-April and can grow 8 cm a day.

Notes

The official scientific name of Japanese knotweed is Polygonum cuspidatum but is has also been called Fallopia japonica and Reynoutria japonica. Some nurseries offer a dwarf variety called P. cuspidatum var. compactum or P. aubertii and goes by common names such as Japanese fleece-flower, Silver Lace Vine, or Silvervine fleece-flower. Giant knotweed, P. sachalinense is also known as Fallopia sachaliensis. The male flowers of Giant knotweed are a viable pollen source for Japanese knotweed, resulting in male, fertile hybrids known as Fallopia bohemica.

Giant knotweed P. sachalinense is very similar to Japanese except in size.

Knotweed key

Key to identification of Invasive Knotweeds in British Columbia - Forest Practices Branch, Ministry of Forests (pdf 904KB)

References

MFR staff observations and comments