Datasheet
Ageratina riparia (mistflower)
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Identity
Top of pagePreferred Scientific Name
- Ageratina riparia (Regel) R. M. King & H. Rob.
Preferred Common Name
Other Scientific Names
- Eupatorium riparium Regel
International Common Names
- English: creeping croftonweed; river-eupatorium; spreading snakeroot
Local Common Names
- Hawaii: hamakua pamakani
- South Africa: mistblom
Summary of Invasiveness
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Ageratina riparia is unpalatable to livestock and is toxic. It reduces the carrying capacity of pastures and rangeland and restricts movement of machinery and stock. The weed has potential for rapid natural spread throughout its potential range (e.g., high reproductive potential and highly mobile propagules). A. riparia is a prolific seeder and grows very fast, becoming the dominant vegetation in an invaded area (Barreto and Evans, 1988). Leachates from leaves and plant litter have an allelopathic effect on other plants. A. riparia is among the primary threats to 25 endangered species on the island of Oahu in Hawaii. The potential negative impacts outweigh any limited value the species has as an ornamental.
A. riparia was added to the US Federal Noxious Weed List and seed list in 2010. Hawaii lists A. riparia as a noxious weed for eradication and control purposes.
Taxonomic Tree
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- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Spermatophyta
- Subphylum: Angiospermae
- Class: Dicotyledonae
- Order: Asterales
- Family: Asteraceae
- Genus: Ageratina
- Species: Ageratina riparia
Description
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A. riparia can be an erect or sprawling herb to small shrub. Stems are cylindrical and have a purplish tint. Its green, opposite leaves can grow up to 15 centimeters long and 4 centimeters wide and range from lanceolate to narrow ovate. Leaves also display toothed margins. Flowers are arranged in flat-topped showy white clusters that produce 5-angled seeds 1-2 millimeters long and topped with 3-4 millimeter long bristles.
Distribution
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A. riparia is a serious pest in Africa, India, Indonesia, Papua New Guinea, Southeast Asia, Australia, New Zealand, Jamaica, Madagascar, and Hawaii. It was introduced to the USA as an ornamental and by agricultural contamination. It is likely to establish populations in the warm southeast USA, particularly in Florida and Texas. Its preferred habitats include misty upland pastures and mountainous areas with high levels of precipitation.
Distribution Table
Top of pageThe 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.
| Country | Distribution | Last Reported | Origin | First Reported | Invasive | References | Notes | ASIA |
| Asia | Present | | | | | USDA-ARS, 2011 | |
AFRICA |
| Madagascar | Present | | Introduced | | | USDA-ARS, 2011 | |
| Mauritius | Present | | Introduced | | | USDA-ARS, 2011 | |
| Réunion | Present | | Introduced | | | USDA-ARS, 2011 | |
| Spain | | | | | | | |
| -Canary Islands | Present | | Introduced | | | USDA-ARS, 2011 | |
NORTH AMERICA |
| Mexico | Present | | Introduced | | | USDA-ARS, 2011 | |
| USA | | | | | | | |
| -Hawaii | Present | | Introduced | | Invasive | USDA-NRCS, 2011; USDA-ARS, 2011 | |
CENTRAL AMERICA AND CARIBBEAN |
| Cuba | Present | | Introduced | | | USDA-ARS, 2011 | |
| Jamaica | Present | | Introduced | | | USDA-ARS, 2011 | |
SOUTH AMERICA |
| Peru | Present | | Introduced | | | USDA-ARS, 2011 | |
OCEANIA |
| Australia | Present | | Introduced | | | USDA-ARS, 2011 | |
| New Zealand | Present | | Introduced | | | USDA-ARS, 2011 | |
Habitat List
Top of page| Category | Habitat | Presence | Status | | Terrestrial-managed |
| Managed grasslands (grazing systems) | Principal habitat | |
| Terrestrial-natural/semi-natural |
| Natural grasslands | Principal habitat | |
Biology and Ecology
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A. riparia is a prolific seeder and grows very fast, becoming the dominant vegetation in an invaded area (Barreto & Evans, 1988). In Australia, mature plants produce between 10,000 and 100,000 seeds annually. The seed can germinate immediately when in light (Parsons and Cuthbertson, 1992). Seeds are dispersed by wind and water. Colonies increase in density and size by horizontal spread and rooting at nodes.
Natural Enemies
Top of page| Natural enemy | Type | Life stages | Specificity | References | Biological control in | Biological control on | | Entyloma ageratinae | Pathogen | | | | Hawaii | |
Pathway Causes
Top of page| Cause | Notes | Long Distance | Local | References | | Hitchhiker | | Yes | | |
| Ornamental purposes | | Yes | | |
Pathway Vectors
Top of page| Vector | Notes | Long Distance | Local | References | | Plants or parts of plants | | Yes | | |
Plant Trade
Top of page| Plant parts liable to carry the pest in trade/transport | Pest stages | Borne internally | Borne externally | Visibility of pest or symptoms | | True seeds (inc. grain) | seeds | No | Yes | |
Impact Summary
Top of page| Category | Impact | | Biodiversity (generally) | Negative |
| Economic/livelihood | Negative |
Risk and Impact Factors
Top of pageImpact mechanisms
- Allelopathic
- Competition - monopolizing resources
Impact outcomes
- Negatively impacts agriculture
- Negatively impacts animal health
- Negatively impacts livelihoods
- Reduced native biodiversity
- Threat to/ loss of endangered species
Invasiveness
- Has high reproductive potential
- Highly mobile locally
- Proved invasive outside its native range
Uses List
Top of pageEnvironmental
- Erosion control or dune stabilization
- Ornamental
Materials
Prevention and Control
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A pest risk assessment completed by APHIS, USA (Lehtonen, 2001) ranked A. riparia as medium in consequences of introduction and high in likelihood of introduction, resulting in an overall ranking of medium/high risk potential and the species was added to the US Federal Noxious Weed List and seed list in 2010. Hawaii lists A. riparia as a noxious weed for eradication and control purposes, which authorizes the State department of Agriculture to conduct control activities for this weed as time and resources permit.
A. riparia is resistant to many herbicides, but can be controlled if treated repeatedly (Parsons and Cuthbertson, 1992). The most effective method of biological control of this weed was the introduction of the fungus, Entyloma ageratinae, to infested areas in the state of Hawaii.
Bibliography
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Barreto, Robert W. and Evans, Harry C. 1988. Taxonomy of a Fungus Introduced into Hawaii for Biological Control of Ageratina riparia (Eupatorieae; Compositae), with Observations on Related Weed Pathogens. Transactions of the British Mycological Society 91: 81-97.
Lehtonen, Polly. 2001. Weed Risk Assessment for Ageratina riparia (Regel) R. M. King and H. Robinson (Mistflower) Version 6 Revised February 22, 2009 by Shirley Wager-Pagé Addendum to a report, Analysis and Assessment of the Invasive risk of Ageratina riparia, submitted by Sarah Reichard and Lizbeth Seebacher, University of Washington, College of Forest Resources, Center for Urban Horticulture. http://www.aphis.usda.gov/plant_health/plant_pest_info/weeds/riskassessments.shtml
Parsons, W. T. & E. G. Cuthbertson. 1992. Noxious weeds of Australia. Inkata Press, Melbourne, Sydney.
Thorp, J.R., Wilson, M (1998 onwards) Weeds Australia - http://www.weeds.org.au/
USDA, NRCS. 2009. The PLANTS Database (http://plants.usda.gov, 15 June 2009). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.
Principal Source
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US Federal Noxious Weed List (draft fact sheet 2011)
Distribution Maps
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- = Present, no further details
- = Evidence of pathogen
- = Widespread
- = Last reported
- = Localised
- = Presence unconfirmed
- = Confined and subject to quarantine
- = See regional map for distribution within the country
- = Occasional or few reports