Limnobium laevigatum | South American spongeplant

California Pest Rating for
Limnobium laevigatum  |  South American spongeplant
Pest Rating: A  |  Proposed Seed Rating: P


Initiating Event:

This plant has been rated as “Q” on the CDFA Plant Pest Rating list for some years

History & Status:

South American spongeplant is a perennial herbaceous aquatic plant native to South America. South American spongeplant is generally free-floating but in situations where the vegetation is dense enough, the leaves may become emergent. It has been found on the San Joaquin River and in the Sacramento-San Joaquin Delta. Spongeplant can form thick mats across the water causing problems for boats, fish, and water infrastructure. It can spread rapidly through quick seed production and vegetative growth. The small, floating seeds easily disperse once produced. It is invasive as it can displace native flora, possibly resulting in habitat impacts on native fauna by reducing oxygen content of bodies of water. Spongeplant populations increase in size rapidly by vegetative reproduction and form dense mats. These mats can infest irrigation canals.

Official Control: An extensive control project has been carried out by the state of California.

California Distribution: South American spongeplant has been found in Alameda, Fresno, Riverside, Shasta, Fresno, Mariposa, and Humboldt Counties. It has been eradicated from some of these counties, but persists in the Delta.

California Interceptions:  Specimens have been sent to CDFA for confirmation.

Consequences of Introduction: 

1.  Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score: 3

—Low (1) Not likely to establish in California; or likely to establish in very limited areas.

—Medium (2) may be able to establish in a larger but limited part of California.

—High (3) likely to establish a widespread distribution in California.

Risk is High (3), as the plant can occur in many wetlands such as the Delta.

2.  Known Pest Host Range: Evaluate the host range of the pest.
Score: 3

—Low (1) has a very limited host range.

—Medium (2) has a moderate host range.

—High (3) has a wide host range.

Risk is high (3) as weeds do not require any one host, but grow wherever ecological conditions are favorable.

3.  Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score: 3

—Low (1) does not have high reproductive or dispersal potential.

—Medium (2) has either high reproductive or dispersal potential.

—High (3) has both high reproduction and dispersal potential.

Risk is High (3). The plant produces via numerous seeds, as well as spreading rapidly in water via vegetative growth. Large rafts of plants can be redistributed by wind to new areas. South American spongeplant is occasionally available in the aquarium trade and such plants could form the nexus for new infestations if discarded or dispersed into wetlands.

4.  Economic Impact: Evaluate the likely economic impacts of the pest to California using the criteria below. Score: 3

A. The pest could lower crop yield.
B. The pest could lower crop value (includes increasing crop production costs).
C. The pest could trigger the loss of markets (includes quarantines).
D. The pest could negatively change normal cultural practices.
E. The pest can vector, or is vectored, by another pestiferous organism.
F. The organism is injurious or poisonous to agriculturally important animals.
G. The organism can interfere with the delivery or supply of water for agricultural uses.

—Low (1) causes 0 or 1 of these impacts.

—Medium (2) causes 2 of these impacts.

—High (3) causes 3 or more of these impacts.

Risk is High (3) as the plant can impede irrigation, boating, fishing, and swimming. It ruins views of water; and effects tourism, threatens water supplies (blocks canals, pumps, dams), and increases flooding.

5.  Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes
B.  The pest could directly affect threatened or endangered species
C.  The pest could impact threatened or endangered species by disrupting critical habitats
D.  The pest could trigger additional official or private treatment programs
E.  Significantly impacting cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score: 3

—Low (1) causes none of the above to occur.

—Medium (2) causes one of the above to occur.

—High (3) causes two or more of the above to occur.

Risk is High (3) as the plant could invade further water systems of California, disrupt natural lake communities and potentially lower biodiversity by covering lake surfaces.  It can block birds’ access to water and suffocate fish and other animals by sealing water surface from air. Dying plants steal oxygen in water.

 Consequences of Introduction to California for South American spongeplant

Add up the total score and include it here. (15)

—Low = 5-8 points

—Medium = 9-12 points

—High = 13-15 points

6.  Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included.
Score: -2

—Not established (0) Pest never detected in California, or known only from incursions.

—Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

—Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

—High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

7.  The final score is the consequences of introduction score minus the post entry distribution and survey information score: (13)


Known invasive in California. Minimal uncertainty.

Conclusion and Rating Justification:

A potentially terrible weed in California. Deserves an A rating as it has invaded certain areas and undoubtedly has the ability to spread much more. Because of this potential future harm, an A rating is justified.


Akers, P. 2010. South American spongeplant. PDF download 3/12/2015:,d.aWc&cad=rja

CalIPC website. Limnobium laevigatum. Accessed 3/12/2015:

Flora of North America Editorial Committee, eds.  1993+.  Flora of North America North of Mexico.  16+ vols.  New York and Oxford.

Global Invasive Species database. Accessed 3/12/2015:

Responsible Party:

Dean G. Kelch, Primary Botanist; California Department of Food and Agriculture; 1220 N Street, Sacramento, CA 95814; Tel. (916) 654-0312;[@]

Comment Period:  CLOSED

The 45-day comment period opened on Tuesday,  May 26, 2015 and closed on July 10, 2015.

Pest Rating:  A  |  Proposed Seed Rating:  P

Posted by ls