Plant Assessment Form

Salvinia molesta

Synonyms: The Salvinia genus is complex of closely-related aquatic ferns that are difficult to distinguish from one another: Salvinia auriculata, S. biloba, S. hertzogii, S. molesta

Common Names: giant salvinia; karibaweed; water velvet; African pyle; aquarium watermoss; water fern; koi kandy

Evaluated on: 3/28/05

List committee review date: 08/07/2005

Re-evaluation date:

Evaluator(s)

Elizabeth Brusati, project manager
California Invasive Plant Council
1442A Walnut St. #462, Berkeley, CA 94709
510-843-3902
edbrusati@cal-ipc.org
Joseph DiTomaso
University of California-Davis
Dept. Plant Sci., Mail Stop 4, Davis, CA 95616
530-754-8715
jmditomaso@ucdavis.edu

List commitee members

Joe DiTomaso
Alison Stanton
Joanna Clines
Cynthia Roye
Doug Johnson

General Comments

No general comments for this species

Table 2. Criteria, Section, and Overall Scores

Overall Score? High
Alert Status? No Alert
Documentation? 3 out of 5
Score Documentation
1.1 ?Impact on abiotic ecosystem processes A Other Published Material
Impact?
Four-part score AAAD Total Score
A
1.2 ?Impact on plant community A. Severe Other Published Material
1.3 ?Impact on higher trophic levels A. Severe Other Published Material
1.4 ?Impact on genetic integrity D. None Other Published Material
2.1 ?Role of anthropogenic and natural disturbance in establishment A. Severe Other Published Material
Invasiveness?
Total Points
17 Total Score A
2.2 ?Local rate of spread with no management A. Increases rapidly Other Published Material
2.3 ?Recent trend in total area infested within state B. Increasing less rapidly Other Published Material
2.4 ?Innate reproductive potential
(see Worksheet A)
A. High Other Published Material
2.5 ?Potential for human-caused dispersal B. Moderate Other Published Material
2.6 ? Potential for natural long-distance dispersal A. Frequent Other Published Material
2.7 ?Other regions invaded C. Already invaded Other Published Material
3.1 ?Ecological amplitude/Range
(see Worksheet C)
C. Limited Other Published Material
Distribution?
Total Score C
3.2 ?Distribution/Peak frequency
(see Worksheet C)
D. Very low Anecdotal

Table 3. Documentation

Scores are explained in the "Criteria for Categorizing Invasive Non-Native Plants that Threaten Wildlands".

Section 1: Impact
Question 1.1 Impact on abiotic ecosystem processes? A Other Published Material
Identify ecosystem processes impacted:

Can form dense mats >0.5m thick that can complete cover the water surface. These mats increase flooding and stagnation while decreasing water quality (1). Impedes oxygen exchange (2). A salvinia infestation can weigh as much as 400 metric tonnes (wet weight) per hectare (2).


Sources of information:

1. DiTomaso, J.M., and E. H. Healy. 2003. Aquatic and Riparian Weeds of the West. University of California, Agriculture and Natural Resources Publication 3421
2. CRC Weed Management. 2003. Weeds of national significance, Weed management guide: Salvinia molesta. Commonwealth Department of the Environment and Heritage (Australia). Available: http://www.deh.gov.au/biodiversity/invasive/publications/pubs/s-molesta.pdf


Question 1.2 Impact on plant community composition,
structure, and interactions?
A Other Published Material
Identify type of impact or alteration:

Thick mats support other vegetation, but displace native vegetation.


Sources of information:

DiTomaso, J.M., and E. H. Healy. 2003. Aquatic and Riparian Weeds of the West. University of California, Agriculture and Natural Resources Publication 3421


Question 1.3 Impact on higher trophic levels? A Other Published Material
Identify type of impact or alteration:

Displaces native animals (1). Creates mosquito habitat, prevents recreational activities such as fishing and boating. Reduction in oxygen exchange makes the water unsuitable for fish. Infestations can be dangerous to animals and people because the floating mats look like solid ground (2).


Sources of information:

1. DiTomaso, J.M., and E. H. Healy. 2003. Aquatic and Riparian Weeds of the West. University of California, Agriculture and Natural Resources Publication 3421
2. CRC Weed Management. 2003. Weeds of national significance, Weed management guide: Salvinia molesta. Commonwealth Department of the Environment and Heritage (Australia). Available: http://www.deh.gov.au/biodiversity/invasive/publications/pubs/s-molesta.pdf


Question 1.4 Impact on genetic integrity? D Other Published Material

None No native species of Salvinia in California.


Sources of information:

Hickman, J. C. (ed.) 1993. The Jepson Manual, Higher Plants of California. University of California Press. Berkeley, CA enter text here


Section 2: Invasiveness
Question 2.1 Role of anthropogenic and natural disturbance
in establishment?
A Other Published Material
Describe role of disturbance:

Inhabits slow-moving waterways. Thrives in nutrient-rich water such as agricultural run-off or wastewater. Does not appear to need disturbance for survival.


Sources of information:

1. CRC Weed Management. 2003. Weeds of national significance, Weed management guide: Salvinia molesta. Commonwealth Department of the Environment and Heritage (Australia). Available: http://www.deh.gov.au/biodiversity/invasive/publications/pubs/s-molesta.pdf


Question 2.2 Local rate of spread with no management? A Other Published Material
Describe rate of spread:

Capable of spreading very fast. Infestations can double every two to three days (1,2).


Sources of information:

1. CRC Weed Management. 2003. Weeds of national significance, Weed management guide: Salvinia molesta. Commonwealth Department of the Environment and Heritage (Australia). Available: http://www.deh.gov.au/biodiversity/invasive/publications/pubs/s-molesta.pdf
2. DiTomaso, J.M., and E. H. Healy. 2003. Aquatic and Riparian Weeds of the West. University of California, Agriculture and Natural Resources Publication 3421


Question 2.3 Recent trend in total area infested within state? B Other Published Material
Describe trend:

New invasion, seems to be increasing, need information.


Sources of information:

CDFA, anecdotal


Question 2.4 Innate reproductive potential? A Other Published Material
Describe key reproductive characteristics:

Aquatic fern. Submerged leaves function and appear as roots. Reproductive structures variable. Some filaments of submerged leaves may develop chains or clusters of tiny ovoid spore-bearing structures. Reproduces vegetatively by stem fragments. Each stem node has up to five dormant nodes. Some protected dormant buds can survive long periods of dry conditions (up to two years has been recorded).


Sources of information:

1. DiTomaso, J.M., and E. H. Healy. 2003. Aquatic and Riparian Weeds of the West. University of California, Agriculture and Natural Resources Publication 3421


Question 2.5 Potential for human-caused dispersal? B Other Published Material
Identify dispersal mechanisms:

Was sold as an aquarium plant or pond ornamental (1). Could also be spread by catching on boats. Some infestations may have been spread deliberately in order to harvest the plants for the aquarium and horticulture trades (2). Not as readily transported at it was in the early 2000s prior to Q rating by CDFA in 2000.


Sources of information:

1. DiTomaso, J.M., and E. H. Healy. 2003. Aquatic and Riparian Weeds of the West. University of California, Agriculture and Natural Resources Publication 3421
2. CRC Weed Management. 2003. Weeds of national significance, Weed management guide: Salvinia molesta. Commonwealth Department of the Environment and Heritage (Australia). Available: http://www.deh.gov.au/biodiversity/invasive/publications/pubs/s-molesta.pdf


Question 2.6 Potential for natural long-distance dispersal? A Other Published Material
Identify dispersal mechanisms:

Can be spread downstream by currents and during floods.


Sources of information:

1. DiTomaso, J.M., and E. H. Healy. 2003. Aquatic and Riparian Weeds of the West. University of California, Agriculture and Natural Resources Publication 3421


Question 2.7 Other regions invaded? C Other Published Material
Identify other regions:

Native to Brazil. Spreading in the southern United States, especially Texas, as far west as the lower Colorado River in Arizona and California (1). A Federal Noxious Weed. The US Army Corps of Engineers calls it "possibly the world's worst weed (2)."A Weed of National Significance in Australia. Also present in Africa, India, Sri Lanka, Southeast Asia, the Philippines, Papua New Guinea, New Zealand, Fiji, and Hawaii (3). Eradication efforts also underway in Mexico. For a time-series map and updates of expansion in the US, see the USGS Salvinia website listed below (4). Restricted to aquatic habitats so invades similar areas in California as it does in other countries.


Sources of information:

1. DiTomaso, J.M., and E. H. Healy. 2003. Aquatic and Riparian Weeds of the West. University of California, Agriculture and Natural Resources Publication 3421
2. US Army Corps of Engineers. No date. Salvinia molesta - Possibly the world's worst weed. US Army Corps of Engineers, Jacksonville District, Aquatic Plant Control Station, Jacksonville, FL. Available: http://www.saj.usace.army.mil/conops/apc.salvinia.pdf
3. CRC Weed Management. 2003. Weeds of national significance, Weed management guide: Salvinia molesta. Commonwealth Department of the Environment and Heritage (Australia). Available: http://www.deh.gov.au/biodiversity/invasive/publications/pubs/s-molesta.pdf
4. US Geological Survey. 2004. Nonindigenous Aquatic Ferns in the United States, Salvinia molesta - Salvinia minima, and their Biological Control,Cyrtobagous salviniae, the Salvinia Weevil. Available: http://salvinia.er.usgs.gov/


Section 3: Distribution
Question 3.1 Ecological amplitude/Range? C Other Published Material

Inhabits still and slow-moving waters of lakes, ponds, reservoirs, rivers, marshes, ditches,and rice fields. Tolerates mild temperate conditions, some salinity, and occasional frost but not prolonged periods of freezing temperatures. Present in canals in the Sonoran Desert (Riverside and Imperial counties), and San Luis Obispo County (1).


Sources of information:

1. DiTomaso, J.M., and E. H. Healy. 2003. Aquatic and Riparian Weeds of the West. University of California, Agriculture and Natural Resources Publication 3421


Question 3.2 Distribution/Peak frequency? D Anecdotal
Describe distribution:

A fairly new invasion.


Sources of information:

CDFA, anecdotal


Worksheet A - Innate reproductive potential

Reaches reproductive maturity in 2 years or less Yes
Dense infestations produce >1,000 viable seed per square meter Yes
Populations of this species produce seeds every year. Unknown
Seed production sustained over 3 or more months within a population annually Unknown
Seeds remain viable in soil for three or more years No
Viable seed produced with both self-pollination and cross-pollination No
Has quickly spreading vegetative structures (rhizomes, roots, etc.) that may root at nodes Yes
Fragments easily and fragments can become established elsewhere Yes
Resprouts readily when cut, grazed, or burned Yes
Total points: 7
Total unknowns: 2
Total score: A?

Related traits:

Does not produce seeds because it's a fern. However, when infestations are dense, produces underwater spores that can disperse long distances. Questions above referring to seeds are answered based on spores.

Worksheet B - Arizona Ecological Types is not included here

Worksheet C - California Ecological Types

(sensu Holland 1986)
Major Ecological Types Minor Ecological Types Code?
Marine Systemsmarine systems
Freshwater and Estuarine lakes, ponds, reservoirsD, < 5%
Aquatic Systemsrivers, streams, canalsD, < 5%
estuaries
Dunescoastal
desert
interior
Scrub and Chaparralcoastal bluff scrub
coastal scrub
Sonoran desert scrub
Mojavean desert scrub (incl. Joshua tree woodland)
Great Basin scrub
chenopod scrub
montane dwarf scrub
Upper Sonoran subshrub scrub
chaparral
Grasslands, Vernal Pools, Meadows, and other Herb Communitiescoastal prairie
valley and foothill grassland
Great Basin grassland
vernal pool
meadow and seep
alkali playa
pebble plain
Bog and Marshbog and fen
marsh and swamp
Riparian and Bottomland habitatriparian forest
riparian woodland
riparian scrub (incl.desert washes)
Woodlandcismontane woodland
piñon and juniper woodland
Sonoran thorn woodland
Forestbroadleaved upland forest
North Coast coniferous forest
closed cone coniferous forest
lower montane coniferous forest
upper montane coniferous forest
subalpine coniferous forest
Alpine Habitatsalpine boulder and rock field
alpine dwarf scrub
Amplitude (breadth): C
Distribution (highest score): D

Infested Jepson Regions

Click here for a map of Jepson regions

  • Central West
  • Sonoran Desert
  • Great Valley
  • Southwest