Photo: Tom Getts

Euphorbia myrsinites Risk Assessment

Synonyms: Tithymalus myrsinites (L.) Hill

Common names: myrtle spurge, creeping spurge

Euphorbia myrsinites -- California

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Created by: Lynn Sweet
Created on: Tuesday, Sep 28th, 2021
Evaluation Summary
This species is an herbaceous perennial introduced as an ornamental species. It has been listed as Noxious in several western states. One common concern is the touch-toxicity of the leaves to humans and animals, and the reduction of forage. It is a low-growing species that can spread "aggressively" but I lacked information from site specifics. Still, many sources agreed that the species spread aggressively and was difficult to control, and some indicated displacement of native species.
General Evaluation Information
Date of Evaluation: 
September 28, 2021
Evaluation Time (hrs): 
3 Hours
Evaluation Status: 
Completed
Plant Information
Plant: 
Euphorbia myrsinites
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: 
AttachmentSize
PDF icon PRE_CA_Matching_Results.pdf503.38 KB
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 shown in USDA plants to be several in many US states, whereas it is native to Central Europe and Asia.
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: 
Many of the observations in Calflora, in northeastern California, and several further south, all inland, appear to be within urban or suburban areas. CDFA in 2017 indicated that there were a few locations but many were under control. Otherwise, the only other worldwide occurrences not in the native region seem to be cultivated based on locality information (three listed in GBIF, in New Zealand and Australia, cultivated per AVH). The best evidence for a "yes" is the Washington State Noxious Weed Control Board's information indicating acres of "infestation" >10 acres in counties in eastern Washington that match the climate using the climate matching tool. This plant has naturalized in Hungary.
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: 
High
Answer / Justification: 
Both Washington and Oregon, USA, which are outside of the native range have the species listed as invasive within their boundaries. "Myrtle spurge escapes cultivation and is aggressive, crowding out native species....Myrtle spurge is an escaped ornamental that inhabits open areas such as fields, rangelands, gardens, disrupted areas, roadsides and waste places." (Washington Noxious Weed Control Board). It is a B rated weed in Oregon (weed of economic importance which is regionally abundant, but which may have limited distribution in some counties). In Colorado, "Myrtle spurge is an invasive ornamental that is native to Eurasia. It is popular with xeriscapes and rock gardens, preferring sunny to partly sunny areas and well drained soils. Myrtle spurge rapidly escapes gardens and invades sensitive ecosystems, out competing native vegetation and wildlife forage." (Colo. Dept. Ag.). In Utah, first person report in newspaper indicates invasive spread. (Nelson).
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: 
The species was evaluated within the region of concern in 2017, where it notes that it is spreading but currently restricted to a few sites, and so was evaluated for potential risk and given an A rating. (CDFA) Both Washington and Oregon, USA, both of which have areas of similar climate to the region of concern, California, have the species listed as invasive within their boundaries. "Myrtle spurge escapes cultivation and is aggressive, crowding out native species....Myrtle spurge is an escaped ornamental that inhabits open areas such as fields, rangelands, gardens, disrupted areas, roadsides and waste places." (Washington Noxious Weed Control Board). It is a B rated weed in Oregon (weed of economic importance which is regionally abundant, but which may have limited distribution in some counties), where invasiveness documentation is less clear: "It doesn’t thrive well in competitive grasslands instead preferring open dry rocky soils..."Populations of myrtle spurge are reported in the NE Oregon counties. It is also reported in Klamath and Wasco counties... Originally planted as a rock garden ornamental, the species has escaped and is spreading on to open lands in dryer parts of the state. Seeds can be ejected when plants are disturbed, sticking to wildlife hair and enabling transport far from the parent plants. Aside from displacing desirable native species, the plant invades playgrounds and parks in some states. " (Oregon Dept of Ag.)
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: 
Very High
Answer / Justification: 
Many euphorbia species have been shown to be weedy or invasive in California, the region of concern, as well as elsewhere in similar climates. One in particular is listed by Cal-IPC as A rated by their PAF process is Euphorbia virgata. Others such as E. terracina, are invasive in limited areas.
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: 
Medium
Answer / Justification: 
Looking at the distribution in the Western US (CA, AZ, WA, OR, UT, NV), most of the area where the species occurs is within a matching climate using the match tool. In the Eastern US, the species ranges further north and more broadly than the narrow region in Appalachia matching the climate in the region of concern. In the native range in Europe, the occurrences generally match the northernmost area of climate match (Spain, France, southern Mediterranean countries), but again it ranges further north into Northern Europe and the UK than the climate match area. It does not occur in the most southern Middle East climate match areas, but does occur in the climate match along the northern edge of that area. Overall, however, there is a >50% climate match.
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: 
Medium
Answer / Justification: 
Noted in Colorado Dept of Ag weed fact sheet, "Myrtle spurge rapidly escapes gardens and invades sensitive ecosystems, out competing native vegetation and reducing wildlife forage." CDFA notes about potential assessed by expert: "In California, Myrtle spurge could disrupt natural bunchgrass and sagebrush scrub communities. Once established, it would trigger additional treatment programs to control it, as in Utah. It would crowd out native species that coexist with or foster rare species." In Utah, newspaper reports seem to detail this type of invasion. "“It grows right over the top of other plants, so there is really no way to stop it,” Frates wrote. “I’m not saying we should stop trying, but the outlook is very, very grim.”" (Nelson)
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: 
Did not find any references to fire or changes in fire regime. Nothing in the CDFA, Washington or Oregon review of the species. This species is a small succulent, diminishing likelihood that it promotes fire.
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: 
High
Answer / Justification: 
The potential for harm to humans and animals was noted in nearly every source summarizing the species. From the Washington Control board: "It also poses dangers to children and adults who come in contact with its caustic latex sap. It causes nausea, vomiting, and diarrhea when ingested. Contact with the skin results in redness, swelling, and blisters (Russell et al. 2002)". From Kelch/CDFA: "Risk is High (3) as Myrtle spurge, where established, lowers the rangeland productivity, is unpalatable to livestock, and, where common, will necessitate herbicide treatments for control. "
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: 
This is a succulent that grows 4-8" high.
Reference(s): 
Reproductive Strategies
11. Does this species (or cultivar or variety) reproduce and spread vegetatively?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Medium
Answer / Justification: 
Washington Noxious Weed Control Board. "It is noted that roots fragmented by cultivation can produce new plants. "
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: 
While it is noted to fragment when in a cultivated situation and re-establish from root fragments, it was not noted as a common method of reproduction in the wildlands. "It is noted that roots fragmented by cultivation can produce new plants. "
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: 
All summaries indicated that this species produces seed. "It has small seeds that can be projected from plant up to 15 feet. Seeds can survive in soil for around 8 years" and "Myrtle spurge is typically spread by seed" (Washington Control Board)
Reference(s): 
14. Does this plant produce copious viable seeds each year (> 1000)?
Yes or No: 
No
Points: 
0
Confidence Level: 
Low
Answer / Justification: 
Photos in the Missouri Plant Finder page show a plant in cultivation with ~30 flowering tips, which appear to have 3 flowers per infloresence, each with probably 3 seeds per lobe of the fruit= 270. Even by upper estimates, it's unlikely this exceeds 1000 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: 
High
Answer / Justification: 
Self-seeding was frequently noted among sources, e.g. "The plant reproduces via numerous, rather large seeds that are thrown some distance from the mother plant. Nevertheless, its ability to disperse seems limited, as populations do not spread rapidly." (Kelch/CDFA). >25% of seed were germinated in controled studies consistently using standard environmental conditions.
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: 
Medium
Answer / Justification: 
The flowers are present on second year stems (Mahr at U Wisconsin Horticulture Extension) It is an herbaceous perennial grown for its showy tips; I see no evidence and it would be unlikely that it does not flower in the first three years. The stems are noted to grow back from the base during the growing season, terminal ends carrying the flowers. "In early spring, new stems emerge from a central taproot. Myrtle spurge flowers in early spring (March and April). The “flower” color ranges from a yellow to a dull pink. The foliage dies back during the winter months" (Washington Noxious Weed Control Board).
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: 
No
Points: 
0
Confidence Level: 
Medium
Answer / Justification: 
Bracts "bloom in spring." (Missouri Botanical Garden). Calflora did not have information on blooming period. North Carolina extension lists the bloom period as a short time in spring, March-April.
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: 
"Seeds can be ejected when plants are disturbed, sticking to wildlife hair and enabling transport far from the parent plants." (Oregon Dept. of Ag.; B rating sheet for E. myrsites). However, I was not sure if there is a mechanism to adhere based on the pictures in the Cristaudo et al. paper, all appearing glabrous and lacking attachment adaptations. And, CDFA notes limited dispersal in the listing documentation. "The plant reproduces via numerous, rather large seeds that are thrown some distance from the mother plant. Nevertheless, its ability to disperse seems limited, as populations do not spread rapidly. " (Kelch/CDFA). Falch, Schönswetter, and Frajman 2019 mention that ants may be capable of spreading it, but dispersal is not that far.
Reference(s): 
19. Are the plant’s propagules frequently dispersed long distance (>100 m) by wind or water?
Yes or No: 
No
Points: 
0
Confidence Level: 
High
Answer / Justification: 
The plant is not associated with riparian areas. It mainly occurs on rocky slopes and open uplands (see collection notes table, Cristaudo et al. and other sources). There is no adaptation for wind dispersal other than the projectile fruit adaptation noted by Kelch/CDFA and Washington Control Board (seeds may be "projected up to 15'" ).
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: 
Very Low
Answer / Justification: 
It is unlikely to be found in commercial crop seed (Kelch/CDFA), and lacks attachment mechanisms for dispersal via vehicles/boats/etc.
Reference(s): 
Evaluation Notes
Notes: 
Total PRE Score

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

PRE Score: 
17
Number of questions answered: 
20
Screener Confidence (%): 
70.0
PRE Content Access and Privacy
Organization: 
2021 Western IPM Grant Project
California Invasive Plant Council (Cal-IPC)
PlantRight
University of California at Riverside
Evaluation visibility: 
Public - accessible to all site users

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