Solanum carolinense_C247-04
Photo courtesy UC Davis Weeds of California

Solanum carolinense Risk Assessment

Common names: Carolina horsenettle

Solanum carolinense -- California

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Evaluation Summary
Summary: 
General Evaluation Information
Date of Evaluation: 
June 16, 2016
Evaluation Time (hrs): 
2 Hours
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: 
USDA does not specify other parts of the world where it is naturalized, but GBIF shows points in Europe, Japan, South America, and New Zealand. Calflora shows it in 15 counties in California. USDA PLANTS lists it as native in California and everywhere else it grows in the US but USDA GRIN does not list California as one of the states where it's native.
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: 
Calflora shows it in 15 counties in California. USDA PLANTS lists it as native in California and everywhere else it grows in the US but USDA GRIN does not list California as one of the states where it's native. This species has a wide range in North America and mostly in areas that are not similar to California. Plants grow in places disturbed by humans or livestock.
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: 
Listed as a B-rated noxious weed in California. Also on the noxious weed lists of Alaska, Arizona, Arkansas, Hawaii, Idaho and Nevada. However, only known from one site in Arizona (SEInet) so the rating may be preventative. Present in Elko County, NV. A B-rated weed in Nevada, meaning "Weeds that are generally established in scattered populations in some counties of the State." Often infests crop fields and pastures (from NV site, although I'm not sure if they are referring to NV specifically).
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: 
Present in Elko County, NV. A B-rated weed in Nevada, meaning "Weeds that are generally established in scattered populations in some counties of the State." Often infests crop fields and pastures (from NV site, although I'm not sure if they are referring to NV specifically). Nevada is similar to California.
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: 
There are four other species of Solanum on the California Noxious Weed List. Large infestations can reduce harvest yield of crops and lower the carrying capacity of pastures by competing with desirable plants for nutrients and soil moisture.
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: 
Very High
Answer / Justification: 
Native to a large area of the eastern and southern US, Ontario (Canada), and northern Mexico. USDA does not specify other parts of the world where it is naturalized, but GBIF shows points in Europe, Japan, South America, and New Zealand. However, most of those are in areas that don't match California.
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: 
Large infestations can reduce harvest yield of crops and lower the carrying capacity of pastures by competing with desirable plants for nutrients and soil moisture. This refers mostly to agricultural areas, not natural areas, but I'm answering yes based on the impacts to pastures.
Reference(s): 
8. Is the plant noted as promoting fire and/or changing fire regimes?
Yes or No: 
No
Points: 
0
Confidence Level: 
High
Answer / Justification: 
Dead stems can remain for several months, so this could produce a fuel load, but there is no mention of this species contributing to 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: 
Very High
Answer / Justification: 
Foliage and berries are toxic to humans and livestock. Dried plant material does not lose its toxicity. Cattle can be poisoned by sheep and goats are more resistant. Large infestations of Solanum spp. can reduce harvest yield of crops and lower the carrying capacity of pastures by competing with desirable plants for nutrients and soil moisture.
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: 
Very Low
Answer / Justification: 
Solanum carolinense is a perennial herb or subshrub that grows 1m tall. It can form dense infestations but I'm not sure if they are enough to be impenetrable.
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: 
Creeping roots produce new shoots and can develop clonal colonies. Horizontal roots extend 1m or more before sending up new shoots. These are true roots and not rhizomes.
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: 
Yes
Points: 
1
Confidence Level: 
Medium
Answer / Justification: 
Stems grow from creeping roots and root fragments are dispersed by cultivation and human activities. This implies that those fragments will regrow.
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: 
Produces yellowish to orange-brown seeds that are wide, smooth, and glossy.
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: 
The average number of seeds per berry is 85. One plant can produce up to 5000 seeds.
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: 
Most seeds are dormant at maturity and require a cool, moist period to break dormancy. However, this sounds like they would germinate after winter in California, i.e. during the next growing season.
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: 
Very High
Answer / Justification: 
Flowering begins one month after new shoots emerge and berries begin to mature 4-8 weeks later.
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: 
Flowers from May through September. Berries mature 4-8 weeks after flowering begins, so seed production begins in June or July. I'm extrapolating to at least three months of seed production.
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: 
Fruits and seeds are dispersed by agricultural activities, water, soil movement and animals.
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: 
Fruits and seeds are dispersed by agricultural activities, water, soil movement and animals.
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: 
Fruits and seeds are dispersed by agricultural activities, water, soil movement and animals. Root fragments disperse with cultivation or other human activities.
Reference(s): 
Evaluation Notes
Total PRE Score

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

PRE Score: 
21
Number of questions answered: 
20
Screener Confidence (%): 
85.0
PRE Content Access and Privacy
Evaluation visibility: 
Public - accessible to all site users

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