Fallopia japonica (herb, shrub)

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Taxonomic name: Fallopia japonica var japonica (Houtt.) Ronse Decraene Synonyms: Fallopia japonica (Houtt.) Dcne., Pleuropterus cuspidatus (Sieb. & Zucc.) Moldenke, Pleuropterus zuccarinii (Small) Small, Polygonum cuspidatum Sieb. & Zucc., Polygonum cuspidatum Sieb. & Zucc. var. compactum (Hook f.) Bailey, Polygonum zuccarinii Small, Reynoutria japonica Houtt. Common names: crimson beauty (English), donkey rhubarb (English), German sausage (English), huzhang (Chinese), itadori (Japanese), Japanese bamboo (English), Japanese fleece flower (English), Japanese knotweed (English), Japanese polygonum (English), kontiki bamboo (English), Mexican-bamboo (English), peashooter plant (English), renouée du Japon (French-France), reynoutria fleece flower (English), sally rhubarb (English) Organism type: herb, shrub Fallopia japonica is an herbaceous perennial native to Japan. It has been introduced to Europe and North America as an ornamental and is also used to stabilise soil, especially in coastal areas. Fallopia japonica requires full sun and is found primarily in moist habitats but also grows in waste places, along roadways and other disturbed areas. Once established, Fallopia japonica forms dense stands that shade and crowd out all other vegetation, displacing native flora and fauna, and the overwintering canes and leaves are slow to decompose. Description Fallopia japonica is an upright, shrub like, herbaceous perennial that can rapidly grow to over 3m in height (Remaley, 1997). Red/purple shoots appear early in spring but as the canes grow, the leaves unfurl and the plant turns green. The mature canes are hollow and have a characteristic pattern of purple speckles. Flowering occurs in late summer/autumn and consists of creamy white flowers. The base of the stem above each joint is surrounded by a membranous sheath. Leaf size is usually about 15cm long by 8 -10cm wide, broadly oval to somewhat triangular and pointed at the tip. Seeds are about 2.5mm long, and are triangular and shiny. The rhizome may extend as deep as 3m and up to 7m away from the parent plant, and is knotty and leathery brown. Fresh rhizome snaps like a carrot and usually possesses a dark orange central core with an orange/yellow outer ring. Both male and female flowers possess vestigial organs of the other sex. Occurs in: coastland, riparian zones, ruderal/disturbed, urban areas, water courses, wetlands Habitat description Fallopia japonica can tolerate a wide range of conditions, including full shade, high temperatures, high salinity and drought. It is found near water sources, such as along river banks, low-lying and disturbed areas. It can colonise coastal shores and islands. In its native range, it grows on volcanic soils with a pH less than 4 (Conolly, 1977, in Seiger, 1991). In the U.S.A., it grows in a variety of soil types, such as silt, loam, and sand, with pH ranging from 4.5 to 7.4. Its distribution appears to be limited by light (Seiger, 1991), and it is found primarily in open sites. General impacts Fallopia japonica is a threat in open and riparian areas where it speads rapidly to form dense stands, excluding native vegetation and prohibiting regeneration. This reduces species diversity and alters habitat for wildlife. Once stands become established, they are extremely persistent and difficult to remove. Uses Fallopia japonica is a popular ornamental worldwide, and is not generally recognised as a weed. In its native range, it is used extensively to obscure waste areas, garbage dumps etc. (Jennings and Fawcett 1980, in Doll and Doll, 1991). It is sometimes used in coastal areas to stabilise soil. The newly emerged shoots are said to be edible (Doll and Doll, 1998), and beekeepers plant it for its abundant nectar secretion (Locandro, 1978, in Doll and Doll, 1998). It leaves were used as a tobacco substitute during World War II. Notes There is some confusion over the taxonomy of F. japonica. In 1777, plant material brought from Japan was named Reynoutria japonica, then in 1846, additional plant material was named Polygonum cuspidatum by Siebold and Zuccarini. In 1901 it was discovered the two plants were identical (Beerling et al. 1994, in Doll and Doll, 1998). It is now known as Polygonum cuspidatum in North America. It is capable of outcompeting plants in its alien range as there are none of the specialist natural enemies that control its population in Japan. Geographical range Native range: Japan. Known introduced range: It has spread through northern and central Europe, most of North America, and has been recorded in Australia and New Zealand. Introduction pathways to new locations Agriculture: Bee keepers have planted it for its abundant nectar secretion (Locandro 1978, in Doll and Doll, 1998). Floating vegetation/debris: For ornamental purposes: F. japonica was introduced from Japan to the United Kingdom as an ornamental in 1825, and from there to North America in the late nineteenth century (Conolly 1977, Patterson 1976, Pridham and Bing 1975, in Seiger, 1991). Ignorant possession: Not recently. Landscape/fauna "improvement": Remaley (1997) states that F. japonica was first introduced as an ornamental and has also been used for erosion control and for landscape screening. Nursery trade: Cause of original invasions. People sharing resources: Imported infested topsoil Taken to botanical garden/zoo: Local dispersal methods Escape from confinement: Remaley (1997) states that discarded cuttings and escapees from neglected gardens are common routes of dispersal from urban areas. Garden escape/garden waste: Natural dispersal (local): Remaley (1997) cites that the plant spreads primarily by vegetative means with the help of its long, stout rhizomes. Rhizomes can regenerate from small fragments and have even been observed to regenerate from internode tissue (Locandro, 1973, in Seiger, 1991). On animals (local): Remaley (1997) states that the rhizomes are carried to a lesser extent by the wind. Seeds are wind dispersed (Maruta, 1976, in Seiger, 1991). Other (local): ill advised control attempts, cause spread of root propagules/stem material People sharing resources (local): Road vehicles: Translocation of machinery/equipment (local): Transportation of habitat material (local): Rhizome dispersal can occur when soil is transported by humans as fill dirt (Conolly 1977, Locandro 1978, in Seiger, 1991). Water currents: Seiger (1991) states that dispersal can occur naturally when rhizome fragments are washed downstream by the current and deposited on banks. Management information Preventative measures: The U.K. Wildlife and Countryside Act states that it is illegal to cause Fallopida japonica to grow in the wild, and it is subject to control legislation in some US states. Physical: Mechanical control methods such as cutting, mowing and pulling can be effective over a long time scale but needs to be consistent, and the disposal of material must be done with care. It is effective for small, initial populations or environmentally sensitive areas where herbicides cannot be used (Remaley, 1997). Chemical: A cut stem treatment method can be used where plants are established within or around non-target plants. The stem should be cut about 5cm above ground level, followed by an immediate application to the cross-section of the stem of a 25% solution of glyphosate (e.g., Roundup, or Rodeo if near wetland areas) or triclopyr (e.g., Garlon). A subsequent foliar application of glyphosate may be required. A foliar spray method can be used to control large populations. It may be necessary to precede foliar applications with stump treatments to reduce the risk of damaging non-target species. Care must be taken when using chemical treatment near water courses. Nutrition In Japan, Fallopia japonica grows slowly but steadily in nutrient poor sites, and rapidly in nutrient rich sites (Hirose, 1984, in Seiger, 1991). It responds well to fertiliser, but growth is considerably slowed in drought conditions (Doll and Doll, 1998). Reproduction Asexual. Dioecious. The primary mode of reproduction in Europe and North America appears to be through extensive rhizomes (Seiger, 1991). Stem material can grow after cutting. It is believed to be clonal in the UK and possibly the USA. Plants can reliably regenerate from less than 5g of root material and the rhizomes beneath a square metre stand of knotweed can produce 238 new shoots. Some clumps of F. japonica will have originated from a single rhizome and will have only one type of flower. Lifecycle stages Rhizomes can regenerate when buried up to 1 metre deep and have been observed growing through 5cm of asphalt (Locandro 1978, Pridham and Bing 1975, in Seiger, 1991). The ability of rhizomes to generate shoots was affected by the source of rhizome fragments as well as fragment size and depth planted, the optimal depth being just below the surface (Locandro 1973, in Seiger, 1991). Adult plants die back at the first frost, leaving the root material to overwinter and provide the stock for the coming year. This species has been nominated as among 100 of the "World's Worst" invaders Reviewed by: Major update under progress Principal sources: Element Stewardship Abstract for Polygonum cuspidatum (Seiger, 1991) Japanese knotweed Polygonum cuspidatum Sieb. & Zucc. (Remaley, 1997) Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG) To contribute information, please contact Shyama Pagad. Last Modified: Monday, 28 November 2005