Salsola ryanii Risk Assessment

Common names: Ryan's Russian thistle

Salsola ryanii -- California

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Created by: Lynn Sweet
Created on: Tuesday, Sep 20th, 2016
Evaluation Summary
Summary: 
General Evaluation Information
Date of Evaluation: 
September 20, 2016
Evaluation Time (hrs): 
2 Hours
Evaluation Status: 
Completed
Plant Information
Plant: 
Salsola ryanii
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: 
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.
Link to Climate Matching Map: 
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: 
The species is newly formed, as a hybrid between two other species. From Welles and Ellstrand 2016: "Salsola ryanii (2n=54) is a newly formed weedy allohexaploid derivative of S. tragus (2n=36) and S. australis (2n=16), which formed in situ in California in the last 20–100 years (Hrusa and Gaskin 2008)." S. tragus: Africa, Asia, Europe S. australis (per Welles & Ellstrand 2016): "Salsola australis is a weed in California and Arizona and is likely native to Australia or South Africa (Borger et al. 2008). Salsola australis is morphologically very similar to S. tragus and was not recognized as a distinct species until recently (Ryan and Ayres 2000). "
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: 
High
Answer / Justification: 
Yes, since this species formed in California, the study region. From Welles and Ellstrand 2015: "Salsola ryanii (2n=54) is a newly formed weedy allohexaploid derivative of S. tragus (2n=36) and S. australis (2n=16), which formed in situ in California in the last 20–100 years (Hrusa and Gaskin 2008)." S. tragus: Africa, Asia, Europe S. australis (per Welles & Ellstrand 2016): "Salsola australis is a weed in California and Arizona and is likely native to Australia or South Africa (Borger et al. 2008). Salsola australis is morphologically very similar to S. tragus and was not recognized as a distinct species until recently (Ryan and Ayres 2000)." Welles and Ellstrand (2016 Am J Bot) identified populations scattered throughout the Central Valley of California, in Southern California, as well as in coastal areas of Northern 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: 
Low
Answer / Justification: 
Hrusa 2008: "Salsola ryanii may be restricted in distribution at least in part due to its intermediacy in the differing ecological adaptations characterizing the parents; fruits do not abscise readily, nor are they persistent; plants tumble to some small extent, but are not dense and orbicular like S. tragus. We feel, based on its current distribution pattern of isolated or extended roadside patches that S. ryanii will likely spread only locally by non-anthropogenic means, but will attain longer distance dispersal via human traffic. Its present adaptive deficiencies will, to some extent, probably restrict its subsequent movement, and the species will unlikely become a widespread future pest."
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: 
Low
Answer / Justification: 
Species noted as having a "rapid population expansion" per Welles and Ellstrand (2016, Am J Bot). They disagree with Hrusa and Gaskin (2008) who indicated possibly limited spread, and note an addition of at least one population per year and "Given this population number expansion in just a decade, it seems likely that the range of S. ryanii will continue to expand and is likely to become an important invasive species. These results strongly contradict the predictions in early studies of S. ryanii that it would not likely become invasive ( Hrusa and Gaskin, 2008). Given the dramatic range increase that has been documented in California, it is also possible that S. ryanii could become an invasive species in other countries through either dispersal of seed of S. ryanii from California or through recurrent formation in other locations where progenitor species co-occur." No other information was available regarding invasiveness of this species.
Reference(s): 
5. Are other species of the same genus (or closely related genera) invasive in a similar climate?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
Salsola tragus and S. paulsenii are C rated noxious weeds in California.
Reference(s): 
California Department of Food and Agriculture (CDFA) (0).  Encycloweedia.
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: 
As above, the species is a result of a hybrid of two other species. This species originated in California, and thus far, only occurs here (GBIF record from the south Pacific is erroneous).
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: 
No
Points: 
0
Confidence Level: 
Low
Answer / Justification: 
No information was available regarding competition of this species with native plants.
Reference(s): 
8. Is the plant noted as promoting fire and/or changing fire regimes?
Yes or No: 
No
Points: 
0
Confidence Level: 
Low
Answer / Justification: 
Indicated to occur on roadsides, but no information regarding promoting ignition or changing fire regimes.
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: 
Low
Answer / Justification: 
Hrusa and Gaskin (2008) list it as a possible moving hazard on roads due to its accumulation at fencelines and other barriers. No information regarding the impact of this species on health or grazing systems was available but Salsola tragus plants are grazed in early stages (UC IPM factsheet on Russian Thistle).
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: 
Low
Answer / Justification: 
Hrusa and Gaskin 2008 note that it accumulates on roadsides and may be a "moving hazard," however, this does not seem to fit the spirit of the question, which would be an impenetrable barrier to livestock (which has not been documented for this species.
Reference(s): 
Reproductive Strategies
11. Does this species (or cultivar or variety) reproduce and spread vegetatively?
Yes or No: 
No
Points: 
0
Confidence Level: 
Medium
Answer / Justification: 
In the botanical and ecological descriptions, vegetative spread is not noted.
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: 
Medium
Answer / Justification: 
The tumbling habit is a mechanism for seed dispersal, not production of new plants via detached fragments of the parent plant.
Reference(s): 
13. Does the species (or cultivar or variety) commonly produce viable seed?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
Welles and Ellstrand (2016, Am J Bot) note that while the homopolyploid hybrid does not produce seed, the allopolyploid hybrid does produce viable seed (collected during the study).
Reference(s): 
14. Does this plant produce copious viable seeds each year (> 1000)?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Medium
Answer / Justification: 
Not from Chris McDonald: If its spreading in CA as suggested in Welles (2016) it should have copious seeds. And I agree with the comment from Ron Vanderhoff, it may be extremely difficult to ID this species, which makes control of this species impractical.
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: 
Confidence Level: 
Answer / Justification: 
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, this is an annual species.
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: 
Medium
Answer / Justification: 
Wilson 2007 notes that fruit matures in the middle of the flowering season (information from Hrusa and Gaskin 2008), while noting the parental species producing seed for a longer period of time. No source found indicates the exact time of seed set. The updated Jepson Manual online (updated in Jepson eFlora) lists June-October as the period of flowering.
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: 
Low
Answer / Justification: 
In the three total published studies on this species, some documentation of dispersal mode is indicated. In none of them are birds or domestic animals identified as significant vectors of spread.
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: 
High
Answer / Justification: 
Noted "tumbling" habit allowing long-distance dispersal. More from Welles and Ellstrand (2016 Am J Bot): "Th e parents vary in their dispersal; S. tragus exhibits the “tumbling” dispersal that is characteristic of the genus, which allows for very long range dispersal, while S. australis is also highly dispersed via wind but does not “tumble” ( Mitchell and Wilcox, 1988 ; Borger et al., 2008 ). The dispersal mode in S. ryanii has not been studied, but the similarities between the progenitors and the neospecies suggest that S. ryanii is also highly dispersed. Because of the evidence for multiple origins and the high level of dispersal in this group, it seems likely that the population expansion documented in this study involves both propagule dispersal and repeated de novo formation of hybrid populations via polyploidy in areas where the two progenitor species have colonized."
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: 
No
Points: 
0
Confidence Level: 
Medium
Answer / Justification: 
One of the parent species (S. tragus) may have been introduced to South Dakota via contaminated seed (Welles and Ellstrand (2016 Evol App) but it is not known to be a primary dispersal mechanism for this species.
Reference(s): 
Evaluation Notes

Not in GRIN or USDA Plants.

Video by UCR: https://www.youtube.com/watch?v=qxPAxD3pxIY#action=share

UC ANR site: http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=21617

Jepson eFlora: http://ucjeps.berkeley.edu/eflora/eflora_display.php?tid=86336

UC IPM factsheet for congeneric: http://ipm.ucanr.edu/PMG/PESTNOTES/pn7486.html

Reviewed by Ron Vanderhoff and Chris McDonald.

Note from Ron Vanderhoff: I believe it should be noted that this is a very new taxa to science and is still very poorly understood. Furthermore, this is a very difficult plant to identify, as are its progenitors, S. australis and S. tragus. Genetic pollution among the three are likely to make invasiveness a very complex and uncertain topic. There is a great concern that existing distribution and abundance information in CA on all of these taxa may be suspect and may have a wide range of error. I do not know if this margin of error would invalidate any of these scores, but it is worth noting.

Total PRE Score

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

PRE Score: 
16
Number of questions answered: 
19
Screener Confidence (%): 
61.1
PRE Content Access and Privacy
Organization: 
California Invasive Plant Council (Cal-IPC)
Evaluation visibility: 
Public - accessible to all site users

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