Photo courtesy of: Neal Kramer (copyright)

Lathyrus latifolius Risk Assessment

Synonyms: Lathyrus megalanthus, Lathyrus membranaceus

Common names: perennial sweet pea, sweet pea, everlasting pea

Lathyrus latifolius -- California

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Evaluation Summary
This plant is a vining perennial with an extensive history in the horticultural industry. It has naturalized throughout the US, and also in Australia and beyond its native range (North Africa/Southern Europe) into Eastern and Northern Europe. The plant is noted as producing monocultures and invading natural areas. However it is heavily associated with disturbed sites and roadsides. It can reproduce by seed but its persistence onsite is due to its extensive production of rhizomes, making it very difficult to control once established.
General Evaluation Information
Date of Evaluation: 
February 10, 2020
Evaluation Time (hrs): 
3 Hours
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: 
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: 
The species has naturalized where it is not native in the eastern Mediterranean region (Cyprus), Northern and central Europe, Australia, and North America.
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: 
Yes. The species has naturalized in 43 counties in the region of interest, California, USA. (Calflora) As well, the species is naturalized in Oregon and Washington, which have a similar climate.
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: 
The plant is listed as being invasive in many areas of the US, primarily referencing roadsides and rights-of-way (Oregon Dept of Ag). Considered to be invasive in some areas in the US (Missouri Botanical Garden) The plant is an environmental weed in Victoria, Australia and on Lord Howe Island, it is listed as an invasive plant that is targeted for eradication. (Weeds of Australia) This was noted as late-season monoculture in the San Francisco area. (R. Kesel, Pers. Comm.)
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: 
Within the region of interest, this was noted as becoming a late-season monoculture in urban areas around San Francisco, and it has been managed in another disturbed preserve in San Francisco. It was also noted that it demonstrates an extremely extensive rhizome network. The plant occurs in the front country of Mt. Tamalpais, Dipsea area, and several highway corridors in Sonoma County (R. Kesel, Pers. Comm.) Within a similar climate, the plant is listed as being invasive in Oregon, primarily referencing roadsides and rights-of-way (Oregon Dept of Ag). Although it is noted that it is mainly a weed of disturbed sites and roadsides where it occurs in Australia, they do mention that it has invaded natural areas as well. The plant is listed as being invasive in Victoria, Australia, some of which matches the climate in California. (Weeds of Australia, Queensland)
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: 
Lathyrus odoratus is noted to be invasive in New Zealand and possibly in the Dominican Republic (CABI). This species has naturalized in California but no information was available about it being invasive. No other Lathyrus are on the noxious weed list in the region of interest.
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: 
The plant is found throughout vast areas of the United States, much of which does not match the region of concern. The areas where it is found in Central, Eastern and Northern Europe and Scandinavia do not match the region of concern. Of the areas reported in Australia and New Zealand, about half of the areas match the climate in the region of concern. (GBIF, Invasive Plants Atlas)
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: 
In Oregon, USA, the plant is known to overtop and smother native vegetation.
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 effects noted having to do with fire. The plant is a low-growing tender perennial, so unlikely to contribute to fire risk substantially.
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: 
Can be toxic to livestock. (DiTomaso et al) USDA GRIN lists it as a vertebrate poison for mammals.
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: 
The plant grows tender foliage and flowers to 4-8" tall, so this is 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: 
Very High
Answer / Justification: 
Rhizomatous growth is a well-known method of reproduction for this species.
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: 
Low
Answer / Justification: 
Since this is a vining species, it is likely that animals moving through the underbrush could easily detach pieces of the vine and deposit them elsewhere, however, this was not noted in any reference.
13. Does the species (or cultivar or variety) commonly produce viable seed?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
The plant is said to easily self-seed.
Reference(s): 
14. Does this plant produce copious viable seeds each year (> 1000)?
Yes or No: 
No
Points: 
0
Confidence Level: 
Medium
Answer / Justification: 
The primary means of reproduction appears to be vegetative. It was noted that seeds were rarely set in greenhouse settings, and seed set in the field is very dependent on pollinators and the abundance of nectar robbers (Godt & Hamrick 1992). The number of ramets in the field far exceeded the number of seedlings. (Hossaert-McKey and Jarry 1992) A study of ovule position in natural populations in Europe showed some variation, but note an average of 10-12 flowers per inflorescence, maturing 0.5-1.5 pods each, and an average of 5-6 viable seeds per pod. This source did not mention the number of infl. per individual, but the numbers would likely be less than 1000 seeds per individual. (Hossaert & Valero 1988)
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: 
There was no mention of specific requirements for germination. Germination rates were listed as high under various conditions listed in Kew Seed Information Database.
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 species didn't flower the first year under controlled conditions in a study that also showed high mortality, so this is probably not typical (Hossaert-McKey & Jarry 1992). The plant is listed in garden blogs/web sales as flowering during the first year, and also unlikely to flower in the first year. None indicated that it would take longer than 3 years for the plant to flower.
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: 
High
Answer / Justification: 
Calflora lists the bloom period as May-September (5 months). Other garden sites list the species as blooming "all summer." "The first flowers of both species appear in late June and early July, and the last pods mature in October. Each of the pink flowers ...stays open during about one week. Fertilized fruits require about one month for maturation." (Hossaert & Valero 1988)
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: 
Low
Answer / Justification: 
Being fairly toxic to wildlife and with the evolution of a violent dehiscion and vegetative reproduction as dispersal, it's unlikely.
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: 
Medium
Answer / Justification: 
The large, heavy seeds are noted to be primarily gravity dispersed. (Godt and Hamrick 1991)
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: 
This is noted to be a roadside weed in Oregon, however, there is no specific mechanism of attachment to vehicles, and it is not noted to be an ag contaminant. Dehiscing violently and gravity seem to be the primary way the seeds disperse.
Reference(s): 
Evaluation Notes
Notes: 
Total PRE Score

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

PRE Score: 
16
Number of questions answered: 
20
Screener Confidence (%): 
70.0
PRE Content Access and Privacy
Evaluation visibility: 
Private - accessible only to organization members

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