Carex pendula_Dean Wm. Taylor_ Ph.D
Photo by Dean W. Taylor

Carex pendula Risk Assessment

Common names: hanging sedge

Carex pendula -- California

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Evaluation Summary
Summary: 
General Evaluation Information
Date of Evaluation: 
March 25, 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: 
Present in 6 California counties. Naturalized in Australia (New South Wales, Victoria) and New Zealand. In the US, present in Washington and Illinois, with an older collection in Virginia along a road. Naturalized in roadsides and stream banks.
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: 
Present in 6 California counties. Naturalized in Australia (New South Wales, Victoria). Present in Washington. DiTomaso and Healy lists as uncommon escape in wetlands in 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: 
Banned in New Zealand, is on their National Pest Plant Accord list due to its ability to displace species in wetland and its prolific seeding ability. Several thousand plants were removed along a stream in Marin County, CA. The USDA risk assessment found limited evidence of invasiveness and gave it a low score but with a high level of uncertainty.
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: 
The areas where it is present in New Zealand do not match California. Several thousand plants were removed along a stream in Marin County, CA, where it spread two miles downstream from an ornamental planting, so it's showing invasive tendencies here. The USDA risk assessment found limited evidence of invasiveness and gave it a low score but with a high level of uncertainty.
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: 
Numerous other Carex species are listed by Randall 2012 but most references are as naturalized, not necessarily invasive. Carex kobomugi is invasive and on noxious weed lists on the east coast of the US, but not in areas matching California. Checked other references and did not find clear information on other Carex that are invasive in areas similar to California. Medium confidence because there are so many Carex species.
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: 
Native to much of Europe, northern Africa and parts of western Asia. There are only a few locations specified in Australia and some of them match California. The native range is split between areas that match California and those that don't. Answering yes but with medium confidence. GBIF = http://www.gbif.org/species/2722051
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: 
Displaces plants along streams. Can form dense infestations. Listed as a prohibited plant in New Zealand for this reason.
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: 
No specific information so defaulting to no.
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: 
Medium
Answer / Justification: 
Grows along streams so would not seem to impact pastures. No mention of it being toxic. Since this species has the potential to from monocultures alongside streams that support T&E salmonids, I am wondering if there might be a potential to harm fish by possibly changing the channel dynamics along the stream edge or by changing diversity of arthropod food sources. I have no idea if this realistic or not, but wanted to throw it out there. - Alison Forrestel
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: 
Medium
Answer / Justification: 
It can produce dense stands but I do not have enough information to count it as impenetrable. USDA found limited reports of impacts around the world. Grows 1-2 m tall.
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: 
Reproduces both by seeds and 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: 
No
Points: 
0
Confidence Level: 
High
Answer / Justification: 
Reproduces from rhizomes but I'm not sure if fragments can regenerate when broken from the parent plant. I haven't personally controlled this species, but others on the GGNRA team have. My understanding from talking with them is that reproduction from fragments is not a concern with this species. - Alison Forrestel
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: 
Yes, a prolific seeder.
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: 
One plant can produce 20,000 seeds with a 90% germination rate.
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: 
The germination rate is 90%. Seeds are dormant during the cold season but it does not sound like they require an especially long dormant period or special conditions to germinate.
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: 
Low
Answer / Justification: 
From USDA/APHIS WRA question ES-13 (Minimum generation time): "This perennial takes 2-5 years to reach its maximum height (RHS, 2011). Given that, it probably reaches reproductive maturity in 2-3 years. Further, because it is herbaceous, it is highly unlikely to take four or more years to reach reproductive maturity. Based on our level of speculation here, the degree of uncertainty is high."
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: 
High
Answer / Justification: 
In California, produces fruits from April to June. In Europe, seeds ripen between June and August.
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: 
High
Answer / Justification: 
Seeds are dispersed primarily by water.
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: 
Seeds are dispersed primarily by water and it often grows along streams.
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: 
High
Answer / Justification: 
Seeds are dispersed primarily by water. Seeds do not have obvious adaptations for transport by vehicles. Being an ornamental by itself is not sufficient for a yes answer.
Reference(s): 
Evaluation Notes

The US Dept of Agriculture Plant Protection and Quarantine program wrote a risk assessment for Carex pendula in 2013 for proposed addition to the federal noxious weed list.  Their full evaluation is available under Weed Risk Assessments at https://www.aphis.usda.gov/aphis/ourfocus/planthealth/plant-pest-and-dis.... Their conclusion was Evaluate Further (i.e. no firm conclusion about invasiveness). USDA estimated that 70% of the US is suitable climate for this species and it is likely to invade primarily riparian areas.

Jepson: http://ucjeps.berkeley.edu/eflora/eflora_display.php?tid=80276

Reviewed by Eric Wrubel and Alison Forrestel, Golden Gate National Recreation Area

Total PRE Score

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

PRE Score: 
17
Number of questions answered: 
20
Screener Confidence (%): 
79.0
PRE Content Access and Privacy
Evaluation visibility: 
Public - accessible to all site users

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