urbpan | 365 Urban Species. #129: Japanese Knotweed (Reply)

Photos by

cottonmanifesto. Location: The Riverway, across from Landmark Center, Boston.

Urban species #129: Japanese knotweed Fallopia japonica or Polygonum cuspidatum *

This plant is rivaled only by phragmites and purple loosestrife in its ability to spread and alter a riparian (river) ecology. Since it was first brought to Boston in 1908 as an ornamental, and planted in later years to stabilize soil, it has become a troublesome part of the landscape. Coastal areas, fence lines, roadsides, and vacant lots are all homes to volunteering Japanese knotweed. Its rhizomes (underground stems) are its main route to overtaking an area and its quick growth in spring and dense coverage are its methods of obstructing competitors. Later in the year knotweed produces vast amounts of tiny white flowers (apparently prized as a nectar source by beekeepers) followed by likewise vast amounts of seeds. Landscape managers wishing to control this invasive species must continually cut back new growth, and if they wish to eventually succeed, inject herbicide into the cut stems.

The dry stalks of the plant persist somewhat into winter, providing brittle perches for overwintering birds. The stalks are hollow tubes, separated by stem nodes (or "knots"), giving a bamboo-like appearance. If cut when fresh and supple, the stems can be used to construct a crude wind chime or pan flute. In the buckwheat family, knotweed is favored by some wild food enthusiasts, who use it either as an asparagus-like vegetable, or in place of its relative, rhubarb. Japanese knotweed has its own "fan" website (it's actually quite well done, and is done with the fact that the plant is invasive in mind) at www.knottybits.com.

* See this page for more information about knotweed's various names. Polygonum cuspidatum is the most commonly used name, but there is good basis to move this species into a separate genus. If this is made official, its new name will be Fallopia japonica