Myoporum laetum_JM DiTomaso
Photo courtesy Joseph DiTomaso

Myoporum laetum Risk Assessment

Common names: ngaio tree; false sandalwood; mousehole tree

Myoporum laetum -- California

Primary tabs

Evaluation Summary
This species is a large, many-branched shrub native to New Zealand. It has been planted worldwide as a landscaping plant. It has been shown to be problematic in California and New Zealand, but published studies documenting ecology and impacts are few although there is anecdotal information available, and much information about its biology from the native range. The species appears to be a prolific seeder and a fast-growing and poisonous species that can outcompete native species. Note that the species was heavily impacted in the landscaping industry by the invasive pest thrips, and this evaluation pertains to the thrips-resistant cultivar, for which there is no specific information available regarding if and how it differs from the originally-imported species. Note that resistance may be conferred by several mechanisms in plants, such as "the presence of a modified epicuticular wax layer on leaves... or by the production of specific compounds such as acylsugars that have a negative effect on insects" (see van Haperen, P., Voorrips, R.E., van Loon, J.J.A. et al. The effect of plant development on thrips resistance in Capsicum. Arthropod-Plant Interactions 13, 11–18 (2019). https://doi.org/10.1007/s11829-018-9645-6). Neither of these characteristics would appear to have any bearing on the evaluated characteristics, below.
General Evaluation Information
Date of Evaluation: 
January 30, 2020
Evaluation Time (hrs): 
Not Recorded
Evaluation Status: 
Submitted
Plant Information
Plant Material: 
If the plant is a cultivar, and if the cultivar's behavior differs from its parent's (behavior), explain how: 
Myoporum laetum Clean n Green is the new Thrips Resistant Coast Myoporum. Other than the resistance to the pest species thrips, it is unclear that there are any differences in the ecology or biology of this cultivar.
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: 
AttachmentSize
PDF icon Matching_Results.pdf515.31 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: 
There are records indicating the plant has naturalized in North America, South America, Europe and a few records exist in Australia and South Africa as well. (GBIF)
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: 
The plant has naturalized in 19 counties in the region of interest, California, USA. (Calflora) Worldwide, the species has naturalized in southern Europe, south Africa (a few records), southern Europe (Spain, France, Portugal, Corsica), and southeastern Australia. (GBIF)
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: 
The full species, plant has been evaluated and listed by Cal-IPC as "Moderate" within the study area. (The plant evaluated here is the thrips-resistant cultivar). (Cal-IPC) Known to be invasive in California (Bossard et al. 2000)
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: 
Very High
Answer / Justification: 
The full species, plant has been evaluated and listed by Cal-IPC as "Moderate" within the study area. (The plant evaluated here is the thrips-resistant cultivar). (Cal-IPC) Known to be invasive in California (Bossard et al. 2000)
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: 
Low
Answer / Justification: 
Did not locate information about other species in this genus being invasive in similar climates. Myoporum acuminatum has been mentioned as a potential invader, but I found no evidence of invasiveness.
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: 
The plant is native to New Zealand with more distribution on the North Island and towards the coast of the South Island, which does not match the climate of the region of interest. (GBIF) The plant has naturalized in 19 counties in/matching the region of interest, California, USA. (Calflora) Worldwide, the species has naturalized in the following that match the region of interest: south Africa (a few records), southern Europe (Spain, France, Portugal, Corsica), and southeastern Australia. (GBIF) The species has naturalized in the following that do not match the region of interest: South America (all occurrences fall outside the narrow band of 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: 
Information in the Cal-IPC plant assessment form for the area of interest, California, indicated observations of this species out-competing native vegetation. (Cal-IPC) This information was also mentioned in a PIER assessment and other sites, but most point to Cal-IPC as the source of the information.
Reference(s): 
8. Is the plant noted as promoting fire and/or changing fire regimes?
Yes or No: 
No
Points: 
0
Confidence Level: 
Very Low
Answer / Justification: 
No information found about 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: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
Most landscaping pages mention that this species is poisonous or toxic to some degree (e.g. Dave's Garden) There are several listings in the FDA Poisonous Plants database, including Bonel-Raposo (et. al. 1998) that describes poisonings in livestock. (FDA Poisonous Plants Database; Bonel-Raposo et al. 1998)
Reference(s): 
10. Does the plant produce impenetrable thickets, blocking or slowing movement of animals, livestock, or humans?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Very High
Answer / Justification: 
"Ngaio can form dense monocultures, shading out competing plants" (Sullivan 2014, citing Bossard 2006)
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: 
I could not locate a good primary source for this information, but several other assessments noted that this plant does not spread vegetatively. (PIER, Cal-IPC) However, one paper does mention root suckers: "There was very little recruitment over this same period and seedlings (and root suckers) were as heavily damaged by Klambothrips as larger plants." (Sullivan 2013)
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: 
Did not find definitive mention of vegetative reproduction, and moreover the personal communications cited in the assessments (observations) did not mention this.
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: 
Noted across the board as producing viable seed. (Kew; Sullivan; and others)
Reference(s): 
14. Does this plant produce copious viable seeds each year (> 1000)?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
Annual seed production per tree was measured (all fruits were counted in a 1/32 arc from which the total per tree was estimated) in South Africa at 20,000-30,000 per tree. (Richards 1988) The seeds are large and only several each per fruit, within drupes (Burrows 1996). Data from seed traps within the native habitat showed only 299 seeds collected in 80 seed traps, ranking it 16th of 46 species studied, while showing a high vegetation importance score at the site (presumably ~density of the species). Each trap had a catching area of 0.196 m2, which totals about 15.6 m2. (Dungan et al 2001)
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: 
No
Points: 
0
Confidence Level: 
Low
Answer / Justification: 
Seeds of this genus noted to germinate readily. (Chinnock) However, Burrows 1996 has an extensive, and difficult to summarize, discussion of the germination behavior in controlled conditions, with potential light-induced dormancy following ready germination by some portion of seeds, and notes dormancy in relatives of the species. Thesis data indicated that the seeds were dormant unless treated (Richards 1988)
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: 
Points: 
Confidence Level: 
Very Low
Answer / Justification: 
PIER did not find/list any information on "years to flower." I could not locate any information on the age at which the plant starts flowering.
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: 
Low
Answer / Justification: 
Bloom time is listed as summer (San Marcos Growers), and listed as April-August, which is 5 months (Calflora). The Cal-IPC PAF answers "no" to this question.
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: 
High
Answer / Justification: 
Moles and Drake (1999) performed a study and the results showed some removal of the fleshy, 4-seeded drupes of this species by rodents in its native range. Seeds are readily eaten by birds (Burrows 1996)
19. Are the plant’s propagules frequently dispersed long distance (>100 m) by wind or water?
Yes or No: 
No
Points: 
0
Confidence Level: 
Low
Answer / Justification: 
The fruits are not adapted for wind dispersal. The species does grow near water and in coastal areas, and the fruit could conceivably float. PIER answers "no" to this question in their assessment.
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: 
The seeds are held within a fleshy drupe and do not appear to have a mechanism for attachment.
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: 
19
Screener Confidence (%): 
67.0
PRE Content Access and Privacy
Evaluation visibility: 
Private - accessible only to organization members

Review this Evaluation

6383

Click on the button below to mark this evaluation as "Reviewed". Once you click the button, please wait a second, and the site will return to this Evaluation and your name will be on the "Reviewers List" in the right hand column (below the Evaluation Summary). For more information, please see the help page on How to Review an Evaluation?

Vertical Tabs