Fallopia japonica (Japanese Knotweed)

Animated Image of Occurrences of Fallopia japonica over Time
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Fallopia japonica, commonly known as Japanese Knotweed, is also known by the scientific names Polygonum cuspidatum and Reynoutria japonica. This rhizomatous perennial invades habitats primarily through vegetative reproduction, though the plants are known to produce abundant showy displays of tiny white flowers followed by abundant amounts of seed.

Japanese Knotweed is native to Asia, and was first introduced to Europe in the mid-18th century by Phillipp Franz Balthasar von Siebold, a Bavarian physician in the Dutch East Indies Army.  Siebold, stationed in Japan, smuggled two shipments of Asian plants home to Europe, and among these was F. japonica, though at the time it was known by a different name. From there, cuttings were introduced into England, and by the late 18th century were being sold in nursery catalogs in the United States (Townsend 1997).

This is yet another example of a plant introduced in the U.S. over one hundred years ago, which has within the past decade become known as one of the more populous invasive plant species. While botanists and horticulturists of the 19th century did realize F. japonica's potential for rapid and persistent growth, it occurred in such isolated populations that its potential for serious habitat alteration must not have been recognized.  Stone (1913) identified both F. japonica and a related species, F. sachalinensis (Giant Knotweed), as becoming naturalized on the grounds of Massachusetts Agricultural College, where they were introduced as potential forage plants.  Bicknell (1908-19) noted that while Japanese Knotweed was growing on the island of Nantucket, it only showed "...some tendency to esacpe from cultivation". The Preliminary Lists of New England Plants - IX Polygonaceae (1902), published in Rhodora, identified F. japonica as being cultivated, but escaped "only in the immediate vicinity of gardens."

Japanese Knotweed is now an exceedingly common site in the urban and suburban landscape of Massachusetts.  It is easily found along roadsides and also in riparian areas, where it thrives in the moist soil and forms new populations when the flow of water breaks off portions of rhizomes or stem growth and sends them downstream.  Land managers have a difficult time removing these plants from areas once they have become established due to the rhizomes that can continually produce more stems.  This species and its relatives (F. sachalinensis and F. baldschuanica) will continue to be a problem for those trying to maintain or preserve ecosystem integrity for many years to come.

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