Photo: Keir Morse

Pulicaria paludosa Risk Assessment

Synonyms: Pulicaria arabica subsp. hispanica, Pulicaria hispanica, Pulicaria uliginosa

Common names: Spanish false fleabane, Spanish sunflower

Pulicaria paludosa -- California

Primary tabs

Created by: Melanie Davis
Created on: Sunday, Sep 17th, 2023
Evaluation Summary
Pulicaria paludosa Link (Asteraceae) is commonly known as Spanish fleabane and is a yellow flowered annual, biennial, or short-lived perennial, growing up to over a meter tall with a woody rhizomatous root system. It is native to the Mediterranean region of Portugal and Spain and was introduced to California where it was first collected in 1946 (Orange County CA) and documented in 1963 (Raven 1963). Exact methods of arrival are unknown, however P. paludosa has since spread across Southern California and now occurs in Clark County Nevada and Western Arizona, favoring disturbed sites along roadsides, wetlands, riparian corridors, and other damp, disturbed sites. An updated review of its designation is warranted, while P. paludosa has been spreading for decades in Southern California, it has only more recently come to the attention of numbers of land managers due to its aggressive spread in riparian areas. Land managers have also found that manual methods of control have been difficult at best and harmful at worst, as P. palidosa appears to benefit from pulling as it will resprout from rhizomes, thus chemical treatment has been prescribed and used in some cases. Where P. paludosa has become established in riparian habitats and created a monoculture, it is considered a threat to rare and species of special concern within riparian habitats and to the riparian species richness community as a whole. Morphological features of the seeds (pappus) and ecological notes indicate that P. paludosa propagules are likely dispersed by wind, water, and soil movement. This species does not appear to pose a threat to the health of livestock or humans.
General Evaluation Information
Date of Evaluation: 
September 17, 2023
Evaluation Time (hrs): 
Not Recorded
Evaluation Status: 
Completed
Plant Information
Plant: 
Pulicaria paludosa
Plant Material: 
If the plant is a cultivar, and if the cultivar's behavior differs from its parent's (behavior), explain how: 
This plant is not a cultivar.
Regional Information
Region Name: 
California
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.
PRE Climate Map (external link)
Climate Matching Maps PDF: 
AttachmentSize
PDF icon ClimateMatch-Pulicaria_paludosa-CA.pdf1.11 MB
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: 
Pulicaria paludosa Link (Asteraceae), commonly known as Spanish fleabane, is an annual, biennial, or short lived perennial plant. It has become naturalized in California and found elsewhere in the United States. It was first collected in 1946 in Orange County, CA and documented in 1963. Since then it has spread across Southern California and now occurs in Clark County Nevada and Western Arizona, favoring disturbed sites along roadsides wetlands, riparian corridors, and other damp, disturbed sites (Raven 1963, USDA 2023). This species has also been recorded as a weed in Western Europe (Williams 1982, Randall 2017) and is a casual alien in the British Isles (Clement 1994). There has been dispute about whether P. paludosa is native or naturalized in the Canary Islands (Acebes-Ginovés et al. 2010, Verloove & Reyes-Betancort 2011). According to the Climate Match Tool (Cal-IPC 2016) P. paludosa has also been found at densities that imply naturalization in Israel/Palestine and Lebanon, however I was unable to find any information to corroborate these findings on GBIF (2023) and current floras of this region list several species of Pulicaria, however Pulicaria paludosa is not present. This indicates that if it does occur in these regions it is at the very least not common enough to be recorded (Danin and Fragman-Sapir 2023).
Reference(s): 
Acebes, J., León M.C., Rodríguez M.L., Aguilar M. Del Arco, García A., Pérez P.L., et al. (2004).  Pteridophyta, Spermatophyta. Lista De Especies Silvestres De Canarias. Hongos, Plantas y Animales Terrestres. 218-220.
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: 
Pulicaria paludosa is native to the Iberian Peninsula in Spain, Portugal, and to Morocco (Galam-Eldin 1981, Verloove & Reyes-Betancort 2011, Cal-IPC 2016) and is found in riparian, marsh, and damp habitats throughout these arid regions (Molina 2017). The climate of nativity to this species is Mediterranean and matches that of California, where it has become naturalized in similar habitat types (Raven 1963, Keil and Stebbins 2012, Randall 2017, USDA 2023). Israel/Palestine and Lebanon also share a similar climate to the native range of P. paludosa and to California, however see concerns from Question 1 about the validity of naturalization of this species in this region.
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: 
Medium
Answer / Justification: 
While Pulicaria paludosa in considered naturalized in several regions (Randall 2017), land managers in Southern California are citing that they are using IPM (integrated pest management) methods of eradication equivalent to an invasive species (CSWRCB 2005, LSA 2021). Because this species creates a monoculture if left unchecked and thus outcompetes native flora it falls under the PRE definition of invasive.
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: 
Medium
Answer / Justification: 
See Question 3 - While it is not considered invasive by the Global Compendium of Weeds (Randall 2017), it is being found in monocultures in Southern California - within the similar climate area - in riparian areas that threaten species of special concern and is being managed as an invasive species (CSWRCB 2005, LSA 2021). Because this species creates a monoculture if left unchecked and thus outcompetes native flora it falls under the PRE definition of invasive.
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: 
The Global Compendium of Weeds (Randall 2017) lists 12 species of Pulicaria and four subspecies, aside from Pulicaria paludosa. None of these are considered invasive or potential harmful to native ecosystems. While some other members of the Pulicaria genus are naturalized outside their home range, the majority are considered weeds or agricultural weeds.
Reference(s): 
6. Is the species (or cultivar or variety) found predominately in a climate matching the region of concern?
Yes or No: 
Yes
Points: 
2
Confidence Level: 
High
Answer / Justification: 
While Pulicaria paludosa is found at lower impact levels in regions that differ from the region of concern, such as Africa, Western Europe and the United Kingdom, the region that this species is native to, and all regions that it is naturalized in, match the climate of concern (Cal-IPC 2016, Randall 2017).
Reference(s): 
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: 
High
Answer / Justification: 
Once established, Pulicaria paludosa can form dense monocultures and crowd out most of the understory species. It occurs in habitats that support special-status species such as southern tarplant (Centromadia parryi var. australis), Coulter's saltbush (Atriplex coulteri), saltspring checkerbloom (Sidalcea neomexicana), white cudweed (Pseudognaphalium leucocephalum), and mud nama (Nama stenocarpum), among others (CSWRCB 2005, CalFlora 2023).
Reference(s): 
8. Is the plant noted as promoting fire and/or changing fire regimes?
Yes or No: 
No
Points: 
0
Confidence Level: 
Medium
Answer / Justification: 
I found no evidence that Pulicaria paludosa can promote or change local fire regimes. One study on the relationships of seed banks and microhabitats under simulated fire in central Spain used P. paludosa as a native study subject and found that, while present in the standing vegetation untreated with fire, it would not germinate in soils treated with heat shock (Torres 2012). While in wet years P. paludosa may contribute to excess biomass promoting the spread of wildfires (Brooks et al 2004), it appears that this is not a species that would become more rigorous in post-fire succession (assuming rhizomes are burned) and likely not greatly alter fire regimes. Additionally, this species likely does not add additional fuel biomass to ecosystems as these riparian habitats already have species capable of burning.
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: 
No
Points: 
0
Confidence Level: 
High
Answer / Justification: 
I found no evidence that Pulicaria paludosa is toxic to humans or animals This species was not listed by CDFA (2015) as a noxious weed and is not included in the Cornell list of poisonous plants (2018) nor listed in the California Poison Control System (2023). P. paludosa is noted to have ethnobotanical medicinal uses in its native range - specifically as a decoction (Vázquez 1997) - indicating that it is not toxic or poisonous to ingest in medicinal quantities. Due to it's presence being restricted to riparian areas, Pulicaria paludosa likely has no to very low impact on grazing systems.
Reference(s): 
10. Does the plant produce impenetrable thickets, blocking or slowing movement of animals, livestock, or humans?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Medium
Answer / Justification: 
Management reports and verified photos of the Pulicaria paludosa (CalFlora 2023, CalPhotos 2023) show that the species can occur in thick monocultures with individuals up to 1 meter tall with available resources. Reports site that it can form dense thickets, making the species an aggressive competitor and management difficult where it has become established (CSWRCB 2005, LSA 2021). Observational and circumstantial evidence shows that monocultures of this species can easily create impenetrable thickets that affect wildlife movement.
Reference(s): 
Reproductive Strategies
11. Does this species (or cultivar or variety) reproduce and spread vegetatively?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Very High
Answer / Justification: 
Pulicaria paludosa is described to have short rhizomes (Keil and Stebbins 2012). This species is reported to be difficult, and almost ineffective, to eradicate manually because pulling and mulching encourages new and regenerative growth from parent plants, root fragments, and rhizomes (CSWRCB 2005).
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: 
Low
Answer / Justification: 
Given the evidence from question 11, this species can reproduce vegetatively, which is assumed to be an effective method for creating monocultures where it is established. Given that, I found no evidence that naturally detached fragments are a common method of reproduction for this species and it is unknown if fragments were move downstream in floods or anthropogenic activities, they would be capable of establishing.
Reference(s): 
13. Does the species (or cultivar or variety) commonly produce viable seed?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Medium
Answer / Justification: 
Management reports state that the species exhibit high success rates and imply that it is through seed dispersal (CSWRB 2005), while there is little available research on the viability of Pulicaria paludosa, there was one study that tested viability in conjunction with pollinator research in P. paludosa's native range. This study found that the average percentage of viable seed per fruit (inflorescence for Asteraceae) was around 10%, where n = 139 'fruits' across 8 sample sites. This study attributes the low viability percentage to an insufficient sample size for effective pollination (Hurtado et al. 2023). The methodology for determining viable seeds in the study could use further investigation as they did not disclose how they determined aster heads to be 'ripe' (before picking and counting in a lab) and then discarded undeveloped seeds. I answered 'yes' to this question because it would seem that viable seed production, while low, is not a rare event as it is an annual or biennial plant with a long flower and fruiting season (CCH2 2023).
Reference(s): 
14. Does this plant produce copious viable seeds each year (> 1000)?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Medium
Answer / Justification: 
Hurtado et al. (2023) found that seeds per fruit averaged around 35, but could well exceed 50. An individual plant can easily have well over 20 flower heads (Keil and Stebbins 2012, Calflora 2023).
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: 
Points: 
0
Confidence Level: 
Very Low
Answer / Justification: 
I am unable to answer this question due to lack of available research.
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: 
This species is an annual or biennial plant, and as such it has the ability to produce viable seed within one year and definitely within the first three years after germination (Raven 1963, Keil and Stebbins 2012)
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: 
Very High
Answer / Justification: 
The peak of flowering time for Pulicaria palidosa is July-October (4 months), and flowering plants have been collected 11 months out of the year (n=149, CCH2 2023).
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: 
No
Points: 
0
Confidence Level: 
Medium
Answer / Justification: 
Pulicaria paludosa has a pappus of bristles, indicating that it relies on wind or water dispersal. This species lacks burrs, hooks, spines or sap that would aid in dispersal animal dispersal (Tikkanen n.d., Keil & Stebbins 2012).
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: 
Medium
Answer / Justification: 
Pulicaria paludosa has a inner and outter pappus of bristles, indicating that it relies on wind or water dispersal (Keil & Stebbins 2012). A management report (CSWRB 2005) observes that the species exhibits success along streams and seasonally wet areas indicating that the pappus of bristles provides buoyancy and seeds can be transported via floods. The morphological features of the pappus also indicate that the species is adapted to long distance wind dispersal. Soil movement is also common in waterways and drainages that Pulicaria paludosa occupies, thus dispersal via soil movement is also a likely vector for dispersal. While I could find no evidence of distances covered by these means, it is very likely that flash flooding events in Southern California can carry seeds far beyond 100 meters. Confidence maintained at 'Medium' due to lack of hard evidence.
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: 
Medium
Answer / Justification: 
While I found no hard evidence that the species could be dispersed by the above methods, spreading range and occupation of disturbed sites along roadsides and in riparian areas frequently used by people indicate that there could be some mode of anthropogenic dispersal, adding evidence that people or vehicles are accidently introducing the species or aiding in the spread of it.
Reference(s): 
Evaluation Notes
Notes: 
Total PRE Score

  • < 13 : Low Potential Risk
  • 13 - 15 : Moderate Potential Risk
  • > 15 : High Potential Risk

PRE Score: 
19
Number of questions answered: 
19
Screener Confidence (%): 
69.0
PRE Content Access and Privacy
Organization: 
2023-2024 Western IPM Project
California Invasive Plant Council (Cal-IPC)
Evaluation visibility: 
Public - accessible to all site users

Review this Evaluation

9172
Note: You have already reviewed this evaluation. Thanks!