Persicaria chinensis
(Chinese knotweed)

Pictures

Picture	Title	Caption	Copyright
Title Habit Caption Persicaria chinensis (Chinese knotweed); habit. Copyright ©Trevor James/Hamilton, New Zealand	Habit	Persicaria chinensis (Chinese knotweed); habit.	©Trevor James/Hamilton, New Zealand
Title Habit Caption Persicaria chinensis (Chinese knotweed); habit. June, 2011. Copyright ©Trevor James/Hamilton, New Zealand	Habit	Persicaria chinensis (Chinese knotweed); habit. June, 2011.	©Trevor James/Hamilton, New Zealand
Title Habit Caption Persicaria chinensis (Chinese knotweed); habit, showing leaves. Copyright ©Trevor James/Hamilton, New Zealand	Habit	Persicaria chinensis (Chinese knotweed); habit, showing leaves.	©Trevor James/Hamilton, New Zealand
Title Leaf Caption Persicaria chinensis (Chinese knotweed); single leaf. July, 2011. Copyright ©Trevor James/Hamilton, New Zealand	Leaf	Persicaria chinensis (Chinese knotweed); single leaf. July, 2011.	©Trevor James/Hamilton, New Zealand
Title Vegetative shoot Caption Persicaria chinensis (Chinese knotweed); vegetative shoot, showing leaves and stems. July, 2011. Copyright ©Trevor James/Hamilton, New Zealand	Vegetative shoot	Persicaria chinensis (Chinese knotweed); vegetative shoot, showing leaves and stems. July, 2011.	©Trevor James/Hamilton, New Zealand
Title Stem and leaf node Caption Persicaria chinensis (Chinese knotweed); stem and leaf node. Copyright ©Trevor James/Hamilton, New Zealand	Stem and leaf node	Persicaria chinensis (Chinese knotweed); stem and leaf node.	©Trevor James/Hamilton, New Zealand
Title Stem and leaf node Caption Persicaria chinensis (Chinese knotweed); stem and leaf node. Copyright ©Trevor James/Hamilton, New Zealand	Stem and leaf node	Persicaria chinensis (Chinese knotweed); stem and leaf node.	©Trevor James/Hamilton, New Zealand
Title Flowering stem Caption Persicaria chinensis (Chinese knotweed); flowering stem. Copyright ©Trevor James-2013/Hamilton, New Zealand	Flowering stem	Persicaria chinensis (Chinese knotweed); flowering stem.	©Trevor James-2013/Hamilton, New Zealand
Title Flower heads Caption Persicaria chinensis (Chinese knotweed); flower heads. Copyright ©Trevor James/Hamilton, New Zealand	Flower heads	Persicaria chinensis (Chinese knotweed); flower heads.	©Trevor James/Hamilton, New Zealand
Title Flower heads Caption Persicaria chinensis (Chinese knotweed); flowers. New Zealand. June, 2013. Copyright ©Trevor James-2013/Hamilton, New Zealand	Flower heads	Persicaria chinensis (Chinese knotweed); flowers. New Zealand. June, 2013.	©Trevor James-2013/Hamilton, New Zealand
Title Flowers Caption Persicaria chinensis (Chinese knotweed); extreme close-up of flowers. New Zealand. June, 2013. Copyright ©Trevor James-2013/Hamilton, New Zealand	Flowers	Persicaria chinensis (Chinese knotweed); extreme close-up of flowers. New Zealand. June, 2013.	©Trevor James-2013/Hamilton, New Zealand
Title New shoots Caption Persicaria chinensis (Chinese knotweed); new shoots. July, 2011. Copyright ©Trevor James/Hamilton, New Zealand	New shoots	Persicaria chinensis (Chinese knotweed); new shoots. July, 2011.	©Trevor James/Hamilton, New Zealand

Identity

Preferred Scientific Name

• Persicaria chinensis (L.) H. Gross

Preferred Common Name

• Chinese knotweed

Other Scientific Names

• Polygonum chinense L.

International Common Names

• English: red bush
• French: empreinte-la-vierge; liane rouge; persicaire de Chine
• Chinese: huo tan mu

Local Common Names

• India: mudanthi; mukkala; oduthan; poovallikod; thiruthanni; thondi
• Thailand: phayaadong

Summary of Invasiveness

P. chinensis is closely related to other important invasive Persicaria species such as P. orientalis, P. capitata, and P. perfoliata, all species included in the Global Compendium of Weeds (Randall, 2012). P. chinensis is a fast-growing herb that forms dense mats and tolerates diverse environmental conditions (Galloway and Lepper, 2010). It spreads by seed and by resprouting from broken fragments. Its high growth rates and spread potential provides this species the ability to smother other plants affecting plant community structure and composition (USDA-APHIS, 2012). Biosecurity New Zealand described the species in a risk assessment as “a highly invasive plant that quickly smothers available surfaces including other plants and trees,” and PIER (2014) lists it as invasive in several territories, including Hawaii.

Taxonomic Tree

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Dicotyledonae
•                     Order: Polygonales
•                         Family: Polygonaceae
•                             Genus: Persicaria
•                                 Species: Persicaria chinensis

Notes on Taxonomy and Nomenclature

Polygonaceae is a well-defined family of flowering plants including 43 genera and 1110 species. Members of the Polygonaceae are diverse in habit ranging from annual and perennial herbs, shrubs to lianas and some trees. The most distinctive feature of the family is the presence of a membranous or hyaline sheath uniting the stipules (Maharajan and Rajendran, 2014). The genus Persicaria was segregated from the genus Polygonum and at present includes approximately 150 species of annual and perennial herbs with taproots or fibrous root systems, and sometimes rhizomes or stolons (Stevens, 2012). 

Description

P. chinensis is a perennial herb. Rhizomes stout. Stems erect, 70-100 cm tall, ligneous at base, much branched, striate, glabrous or retrorsely hispid. Petiole 1-2 cm, usually auriculate at base, upper leaves subsessile; leaf blade ovate, elliptic, or lanceolate, 4-16 × 1.5-8 cm, both surfaces glabrous or hispid, abaxially sometimes pubescent along veins, base truncate or broadly cordate, margin entire, apex shortly acuminate; ocrea tubular, 1.5-2.5 cm, membranous, glabrous, much veined, apex oblique, not ciliate. Inflorescence terminal or axillary, capitate, 3-5 mm, usually several capitula aggregated and panicle-like; peduncle densely glandular hairy; bracts broadly ovate, each 1-3-flowered. Perianth white or pinkish, 5-parted; tepals ovate, accrescent in fruit, becoming blue-black, fleshy. Stamens 8, included. Styles 3, connate to below middle. Achenes included in persistent perianth, black, opaque, broadly ovoid, trigonous, 3-4 mm (Flora of China Editorial Committee, 2014). 

Plant Type

Distribution

P. chinensis is native to much of Asia (Flora of China Editorial Committee, 2014; Maharajan and Rajendran, 2014; USDA-ARS, 2014), but it has been introduced to other geographic areas including Pakistan, Hawaii, Jamaica, La Réunion, and Singapore (Wagner et al., 1999; Kairo et al., 2003; USDA-APHIS, 2012; PIER, 2014). In New Zealand, this species was recently eradicated (Galloway and Lepper, 2010).

Distribution Table

The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

History of Introduction and Spread

P. chinensis behaves as an environmental and agricultural weed and thus it was probably introduced into new habitats accidentally. In Jamaica, this species appears in herbarium collections made in 1905 (US National Herbarium). In the USA, it has previously been reported as introduced in Maryland, Massachusetts, and New Jersey (USDA-APHIS, 2012) and it appears in collections made in those states in the 1990s, but is unclear if it is truly established in those areas and the current USDA-NRCS (2014) database does not list it as present in the USA other than in Hawaii.
 

Risk of Introduction

The risk of introduction of P. chinensis is moderate. Even when this species is not used in cultivation or in commercial trade (horticultural, ornamental, or other), it might be introduced and/or dispersed by people for use as a medicinal herb (USDA-ARS, 2014). In addition, P. chinensis is a fast-growing herb that behaves as a weed and has the capability to tolerate diverse environmental conditions. Therefore, it has the potential and the traits necessary to spread into new habitats (USDA-APHIS, 2012; PIER, 2014). 

Habitat

Within its native distribution range, P. chinensis grows in wet valleys, grassy slopes, mixed forests, thickets in valleys, and mountain slopes from sea level to 3000 m (Flora of China Editorial Committee, 2014). Outside its native distribution range, it can be found growing in disturbed open areas, home gardens, abandoned gardens, riverbanks, and roadsides (Galloway and Lepper, 2010). It also grows as a weed in agricultural lands and tea plantations (Tjitrosemito and Jaya, 1990; Wagner et al., 1999). The species can tolerate a wide range of environmental conditions including shade, high temperatures, high salinity and drought.

Habitat List

Hosts/Species Affected

P. chinensis is a common weed requiring control in tea plantations where it covers tea bushes and blocks drainage systems (Tjitrosemito and Jaya, 1990). 

Host Plants and Other Plants Affected

Growth Stages

Biology and Ecology

Genetics

The chromosome number reported for P. chinensis varies from 2n = 22 to 2n = 32 depending of the location (Subramanian, 1980; Flora of China Editorial Committee, 2014).

Reproductive Biology and Phenology

In China, P. chinensis has been recorded flowering from July to November and fruiting from July to December (Flora of China Editorial Committee, 2014). In Pakistan, this species flowers from September to November (Flora of Pakistan, 2014) and in India from September to December (India Biodiversity, 2014). 

Climate

Soil Tolerances

Soil drainage

• free

Soil reaction

• neutral

Soil texture

• light
• medium

Natural enemies

Notes on Natural Enemies

In West Java, larvae and adults of Haltica sp. (Coleoptera: Halticidae) cause considerable damage to plants of P. chinensis. Biological control using this beetle species has been proposed for the control of P. chinenses when it grows as a weed in tea plantations (Tjitrosemito and Jaya, 1990). 

Means of Movement and Dispersal

P. chinensis spreads by seeds. Seeds are dispersed by birds and accidentally and/or intentionally by people. It is also able to spread vegetatively by resprouting from broken fragments (USDA-APHIS, 2012).

Pathway Causes

Pathway Vectors

Impact Summary

Economic Impact

P. chinensis is an important weed in tea production in its native distribution range (Tjitrosemito and Jaya, 1990), covering tea bushes and blocking drainage systems (USDA-APHIS, 2012).. 

Environmental Impact

P. chinensis is a fast-growing weed that may disrupt regeneration and successional processes and outcompete native vegetation. This species is an environmental and agricultural weed that grows forming dense mats which suppress other plant species. P. chinensis also has the ability to smother native plants, potentially affecting plant community structure and composition (USDA-APHIS, 2012). 

Risk and Impact Factors

• Proved invasive outside its native range
• Has a broad native range
• Abundant in its native range
• Highly adaptable to different environments
• Is a habitat generalist
• Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
• Pioneering in disturbed areas
• Benefits from human association (i.e. it is a human commensal)
• Long lived
• Fast growing

• Ecosystem change/ habitat alteration
• Modification of successional patterns
• Negatively impacts agriculture
• Reduced native biodiversity

• Competition - monopolizing resources
• Competition - smothering
• Rapid growth
• Rooting

• Highly likely to be transported internationally accidentally
• Difficult to identify/detect as a commodity contaminant

Uses

P. chinensis is used in traditional Asian medicine. In Malaysia it is used as a herbal medicine  to treat stomach-ache, eczema, and eye disease, and as a depurative herb (USDA-ARS, 2014). 

Uses List

Medicinal, pharmaceutical

• Traditional/folklore

Prevention and Control

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

In West Java, one study showed that Haltica sp. (Coleoptera: Halticidae) is a promising candidate as a biological control agent. However, the authors suggest that further studies are needed especially on the Haltica host range before deciding to recommend it as a biological control agent of P. chinensis (Tjitrosemito and Jaya, 1990). USDA-APHIS (2012) found no evidence for control activities for this plant in natural areas.

References

Chong KY; Tan HTW; Corlett RT, 2009. A checklist of the total vascular plant flora of Singapore: native, naturalised and cultivated species. Singapore: Raffles Museum of Biodiversity Research, National University of Singapore, 273 pp. http://lkcnhm.nus.edu.sg/nus/pdf/PUBLICATION/LKCNH%20Museum%20Books/LKCNHM%20Books/flora_of_singapore_tc.pdf

Flora of China Editorial Committee, 2014. Flora of China. St. Louis, Missouri and Cambridge, Massachusetts, USA: Missouri Botanical Garden and Harvard University Herbaria. http://www.efloras.org/flora_page.aspx?flora_id=2

Flora of Pakistan, 2014. Flora of Pakistan/Pakistan Plant Database (PPD). Tropicos website St. Louis, Missouri and Cambridge, Massachusetts, USA: Missouri Botanical Garden and Harvard University Herbaria. http://www.tropicos.org/Project/Pakistan

Galloway DJ; Lepper VE, 2010. Persicaria chinensis - a new alien Asian invader? In: 17th Australasian weeds conference. New frontiers in New Zealand: together we can beat the weeds. Christchurch, New Zealand, 26-30 September, 2010 [ed. by Zydenbos, S. M.]. Hastings, New Zealand: New Zealand Plant Protection Society, 174-175.

Imada CT; James SA; Kennedy BH, 2008. New plant records from Herbarium Pacificum for 2007. Bishop Museum Occasional Papers 100, 100:12-16. [Records of the Hawaii Biological Survey for 2007.] http://hbs.bishopmuseum.org/pubs-online/pdf/op100.pdf

India Biodiversity, 2014. Online Portal of India Biodiversity. http://indiabiodiversity.org/species/list

Kairo M; Ali B; Cheesman O; Haysom K; Murphy S, 2003. Invasive species threats in the Caribbean region. Report to the Nature Conservancy. Curepe, Trinidad and Tobago: CAB International, 132 pp. http://www.issg.org/database/species/reference_files/Kairo%20et%20al,%202003.pdf

Maharajan M; Rajendran A, 2014. Taxonomic studies on selected species of the genus Polygonum L. (Polygonaceae) in South India. Journal of Science, 4:144-148. http://www.journalofscience.net/File_Folder/144-148.pdf

PIER, 2014. Pacific Islands Ecosystems at Risk. Honolulu, USA: HEAR, University of Hawaii. http://www.hear.org/pier/index.html

Randall RP, 2012. A Global Compendium of Weeds. Perth, Australia: Department of Agriculture and Food Western Australia, 1124 pp. http://www.cabi.org/isc/FullTextPDF/2013/20133109119.pdf

Stevens PF, 2012. Angiosperm Phylogeny Website. http://www.mobot.org/MOBOT/research/APweb/

Subramanian D, 1980. Cyto-taxonomical studies in South Indian Polygonaceae. Proceedings of the Indian Science Congress Association, 67:50-51.

Tjitrosemito S; Jaya S, 1990. The role of Haltica sp (Coleoptera: Halticidae) as biological control agent of Polygonum chinense. Biotropia, 4: 41-48.http://journal.biotrop.org/index.

USDA-APHIS, 2012. Weed Risk Assessment for Persicaria chinensis (L. Gross (Polygonaceae) - Chinese knotweed. Raleigh, NC, USA: USDA-APHIS, 18 pp.

USDA-ARS, 2014. Germplasm Resources Information Network (GRIN). Online Database. Beltsville, Maryland, USA: National Germplasm Resources Laboratory. https://npgsweb.ars-grin.gov/gringlobal/taxon/taxonomysearch.aspx

USDA-NRCS, 2014. The PLANTS Database. Baton Rouge, USA: National Plant Data Center. http://plants.usda.gov/

Wagner WL; Herbst DR; Sohmer SH, 1999. Manual of the flowering plants of Hawaii. Revised edition. Honolulu, Hawaii, USA: University of Hawaii Press/Bishop Museum Press, 1919 pp.

Links to Websites

Contributors

01/12/14 Original text by:

Julissa Rojas-Sandoval, Department of Botany-Smithsonian NMNH, Washington DC, USA

Pedro Acevedo-Rodríguez, Department of Botany-Smithsonian NMNH, Washington DC, USA

Distribution Maps