Parthenium hysterophorus_Ron Vanderhoff
Photo by Ron Vanderhoff

Parthenium hysterophorus Risk Assessment

Common names: Santa Maria feverfew

Parthenium hysterophorus -- California

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Evaluation Summary
Summary: 
General Evaluation Information
Date of Evaluation: 
January 27, 2016
Evaluation Time (hrs): 
Not Recorded
Evaluation Status: 
Completed
Plant Information
Plant Material: 
If the plant is a cultivar, and if the cultivar's behavior differs from its parent's (behavior), explain how: 
Regional Information
Region Name: 
Climate Matching Map
These maps were built using a toolkit created in collaboration between GreenInfo Network, PlantRight, Cal-IPC, and Agricultural Sustainability Institute at UC Davis.
Climate Matching Maps PDF: 
Invasive History and Climate Matching
1. Has the species (or cultivar or variety, if applicable; applies to subsequent "species" questions) become naturalized where it is not native?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Very High
Answer / Justification: 
California, Hawaii, midwestern/eastern/southern US, Africa, Asia, Australia, Pacific Islands. (Native to Mexico and much of South America.)
Reference(s): 
2. Is the species (or cultivar or variety) noted as being naturalized in the US or world in a similar climate?
Yes or No: 
Yes
Points: 
2
Confidence Level: 
Very High
Answer / Justification: 
One record from an agricultural field at UC Riverside in 1981. A second colony was recently detected and confirmed by CDFA in Santa Ana, Orange County, CA. A third very small infestation of two plants has also been detected in Irvine, Orange County, CA. Naturalized in the KwaZulu-Natal region of South Africa, which matches California.
Reference(s): 
3. Is the species (or cultivar or variety) noted as being invasive in the U.S. or world?
Yes or No: 
Yes
Points: 
2
Confidence Level: 
Very High
Answer / Justification: 
Aggressively colonizes disturbed sites. Affects the production of crops. Invasive in northern KwaZulu-Natal, South Africa, where it is called famine weed due to its (potential?) impacts on crops. Noxious weed in Puerto Rico. Invasive in India, environmental weed in Australia (Randall 2012). CABI says it's a declared noxious weed in Queensland, AU, but the Queensland website says only that it invades pastures, floodplains, grasslands, open woodlands, waste areas, disturbed sites, lawns, gardens and crops (no legal listing).
Reference(s): 
4. Is the species (or cultivar or variety) noted as being invasive in the US or world in a similar climate?
Yes or No: 
Yes
Points: 
3
Confidence Level: 
High
Answer / Justification: 
Invasive in northern KwaZulu-Natal, South Africa, where it is called famine weed due to its (potential?) impacts on crops.
Reference(s): 
5. Are other species of the same genus (or closely related genera) invasive in a similar climate?
Yes or No: 
No
Points: 
0
Confidence Level: 
Medium
Answer / Justification: 
Randall 2012 lists several other Parthenium spp as weeds (agricultural) but I could not find details.
Reference(s): 
6. Is the species (or cultivar or variety) found predominately in a climate matching the region of concern?
Yes or No: 
No
Points: 
0
Confidence Level: 
Medium
Answer / Justification: 
Prefers climates classified as Cf, Cs, Cw in the Trewartha-Koppen climate system. Cs = Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers (according to CABI data). These are climate zones that match California. However, most locations on GBIF map (http://www.gbif.org/species/3086784) are in portions of Central America, South America, Asia and Australia that do not match California based on Cal-IPC's climate map.
Impact on Native Plants and Animals
7. Does this plant displace native plants and dominate (overtop or smother) the plant community in areas where it has established?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Very High
Answer / Justification: 
Allelopathic properties allow it to suppress native vegetation in a wide range of habitats.
Reference(s): 
8. Is the plant noted as promoting fire and/or changing fire regimes?
Yes or No: 
No
Points: 
0
Confidence Level: 
Very High
Answer / Justification: 
Can find no mention of this, despite the thorough description in the CABI datasheet.
Reference(s): 
9. Is the plant a health risk to humans or animals/fish? Has the species been noted as impacting grazing systems?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Very High
Answer / Justification: 
This weed is considered to be a cause of allergic respiratory problems, contact dermatitis, mutagenicity in human and livestock. Crop production is drastically reduced owing to its allelopathy.
Reference(s): 
10. Does the plant produce impenetrable thickets, blocking or slowing movement of animals, livestock, or humans?
Yes or No: 
No
Points: 
0
Confidence Level: 
High
Answer / Justification: 
Based on herbarium specimens in Tropicos, and that it's an annual herb, it does not seem large enough to create 'impenetrable" thickets.
Reference(s): 
Missouri Botanical Garden (2015).  Tropicos.
Reproductive Strategies
11. Does this species (or cultivar or variety) reproduce and spread vegetatively?
Yes or No: 
No
Points: 
0
Confidence Level: 
Very High
Answer / Justification: 
It is unable to reproduce vegetatively from plant parts or by apomixis.
Reference(s): 
12. If naturally detached fragments from this plant are capable of producing new plants, is this a common method of reproduction for the plant?
Yes or No: 
No
Points: 
0
Confidence Level: 
Very High
Answer / Justification: 
It is unable to reproduce vegetatively from plant parts or by apomixis.
Reference(s): 
13. Does the species (or cultivar or variety) commonly produce viable seed?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Very High
Answer / Justification: 
A prolific seed producer. Produces 10,000 to 15,000 viable seeds per plant.
Reference(s): 
14. Does this plant produce copious viable seeds each year (> 1000)?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Very High
Answer / Justification: 
Produces 10,000 to 15,000 viable seeds per plant.
Reference(s): 
15. Is there significant germination (>25%) of seeds the next growing season, with no requirement of an infrequent environmental condition for seeds to germinate (i.e. fire) or long dormancy period?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Very High
Answer / Justification: 
In Australia, parthenium weed germinates mainly in spring and early summer. It produces flowers and seeds throughout its life and dies in late autumn. Flowering may begin as early as 4 weeks after seedling emergence and plants continue to flower for extended periods (6-8 months) when conditions permit.
Reference(s): 
16. Does this plant produce viable seed within the first three years (for an herbaceous species) to five years (for a woody species) after germination?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
Yes. Annual or short-lived perennial so it must produce seeds within the first three years.
Reference(s): 
17. Does this plant continuously produce seed for >3 months each year or does seed production occur more than once a year?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
In Australia, parthenium weed germinates mainly in spring and early summer. It produces flowers and seeds throughout its life and dies in late autumn. Flowering may begin as early as 4 weeks after seedling emergence and plants continue to flower for extended periods (6-8 months) when conditions permit.
Reference(s): 
Dispersal
18. Are the plant’s propagules frequently dispersed long distance (>100 m) by mammals or birds or via domestic animals?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Very High
Answer / Justification: 
Has small and light seeds that are capable of long distance travel via wind, water, birds, vehicles, farm machinery and other animal traffic.
Reference(s): 
19. Are the plant’s propagules frequently dispersed long distance (>100 m) by wind or water?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Very High
Answer / Justification: 
Has small and light seeds that are capable of long distance travel via wind, water, birds, vehicles, farm machinery and other animal traffic.
Reference(s): 
20. Are the plant’s propagules frequently dispersed via contaminated seed (agriculture or wildflower packets), equipment, vehicles, boats or clothing/shoes?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Very High
Answer / Justification: 
Has small and light seeds that are capable of long distance travel via wind, water, birds, vehicles, farm machinery and other animal traffic. Also transported in garden waste.
Reference(s): 
Evaluation Notes

Reviewed by Barbara Castro, CA Dept of Water Resources

Direct link to CABI datasheet, Updated 4 Nov. 2015. http://www.cabi.org/isc/datasheet/45573

Queensland factsheet:

Total PRE Score

  • < 13 : accept (low risk of invasiveness)
  • 13 - 15 : evaluate further
  • > 15 : reject (high risk of invasiveness)

PRE Score: 
18
Number of questions answered: 
20
Screener Confidence (%): 
92.0
PRE Content Access and Privacy
Evaluation visibility: 
Public - accessible to all site users

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