Acaena novae-zelandiae_C226-04
Photo: UC Davis Weeds of California

Acaena novae-zelandiae Risk Assessment

Common names: biddy-biddy

Acaena novae-zelandiae -- California

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Created by: Elizabeth D. Brusati
Created on: Thursday, Jan 21st, 2016
Evaluation Summary
Summary: 
General Evaluation Information
Date of Evaluation: 
January 21, 2016
Evaluation Time (hrs): 
3 Hours
Evaluation Status: 
Completed
Plant Information
Plant: 
Acaena novae-zelandiae
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: 
California and Oregon and Ireland. GBIF map also shows locations in Great Britain and Papua New Guinea (http://www.gbif.org/species/5370755).
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: 
Naturalized in 10 counties 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: 
Listed on California and Oregon noxious weed lists. In SW Oregon, it is invasive in open, disturbed sites such as dunes and grassy areas. Competes with native plants on coastal bluffs where it forms dense mats.
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: 
In SW Oregon, it is invasive in open, disturbed sites such as dunes and grassy areas. Competes with native plants on coastal bluffs where it forms dense mats. Can't find other information specifically calling it invasive. Personal communication from Steve Schoenig, formerly of the CDFA noxious weed program, that it was added to California's noxious weed list due to impacts on the sheep industry because burrs stick in wool and make it unsellable. I couldn't find other information to confirm this.
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: 
Acaena agnipila listed as environmental weed in Global Compendium. Pg. 77 - Somewhere in NZ? Other spp listed as naturalized but not specifically invasive. Answering No because most of New Zealand does not match California based on Cal-IPC's climate map and New Zealand is the native range according to USDA.
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: 
Medium
Answer / Justification: 
Native to Australia (Tasmania, New South Wales, Queensland, South Australia, Victoria) and New Zealand. Naturalized in California, two counties in SW Oregon, Ireland, Great Britain, and Papua New Guinea. Based on GBIF's map and Cal-IPC's climate map, the areas in Australia and some of New Zealand match California well, as does Oregon. Britain, Ireland, Papua New Guinea and the rest of New Zealand does not. Answering no because I don't think it qualifies as predominantly; it's about equal.
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: 
Plants grow clustered together forming large mats where individuals are indistinguishable. In SW OR, competes with native plants on coastal bluffs.
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: 
No mention of this and it prefers moist habitats such as near the coast, so seems unlikely.
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: 
This genus is not listed in the FDA Poisonous Plants Database.
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: 
Low-growing species that is less than one foot tall, so this seems unlikely
Reference(s): 
Reproductive Strategies
11. Does this species (or cultivar or variety) reproduce and spread vegetatively?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
Woody stolons root at nodes
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: 
Individual plants also spread through clonal growth and can reproduce vegetatively if rooted stolons are separated from the parent plant by mechanical damage (Gynn and Richards 1985). Spread may also occur from the trade of the species as an ornamental (Risk Assessment for Great Britain).
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: 
reproduction by seed
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 large plant can produce hundreds of seed heads with 70-100 seeds per head, so extrapolating that to more than 1000/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: 
Medium
Answer / Justification: 
Yes based on the fact that there is no indication that the plant has a dormancy period or requires a process such as scarification 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: 
Medium
Answer / Justification: 
Assuming yes based on the fact that it's a fairly small herbaceous plant
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 February-September in California so assuming seeds are produced in that period as well.
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: 
Clinging burs have the potential to be transported by animals or humans
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: 
Most fruits do not disperse far from parent plant.
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: 
High
Answer / Justification: 
Clinging burs could attach to clothing. It is believed to have reached Oregon as a contaminant in wool.
Reference(s): 
Evaluation Notes

Reviewed by Steve Schoenig, CA Dept of Fish and Wildlife (retired) and Gina Darin (CA Dept. of Water Resources)

Total PRE Score

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

PRE Score: 
18
Number of questions answered: 
20
Screener Confidence (%): 
79.0
PRE Content Access and Privacy
Organization: 
California Invasive Plant Council (Cal-IPC)
Evaluation visibility: 
Public - accessible to all site users

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