Plant Assessment Form

Myriophyllum spicatum

Common Names: spike watermilfoil

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 AAAU 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 U. Unknown Other Published Material
2.1 ?Role of anthropogenic and natural disturbance in establishment A. Severe Other Published Material
Invasiveness?
Total Points
18 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 Observational
2.4 ?Innate reproductive potential
(see Worksheet A)
A. High Other Published Material
2.5 ?Potential for human-caused dispersal A. High 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 B
3.2 ?Distribution/Peak frequency
(see Worksheet C)
B. Moderate Observational

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:

Forms large surface or subsurface mats that impede wateflow (1). Dense canopies result in reduced oxygen exchange, increased nutrient loading, and increased water temperatures. There is concern that watermilfoil might mobilize phosphorous in Lake Tahoe, which is currently phosphorous limited, contributing to the loss of clarity in the lake (2).


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.
2. Donaldson, S. 1997. Flood-borne noxious weeds: impacts on riparian areas and wetlands. Proceedings of the California Exotic Pest Plant Council Symposium. 3:7 Available: http://groups.ucanr.org/ceppc/Symposia/


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

Large mats displace native aquatic 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:

Large floating mats create mosquito habitat and impede recreational activities (1). Provides calm water for waterfowl, but simultaneously outcompetes native vegetation that supports waterfowl. One study in New York found that as watermilfoil cover increased from 35% to 97%, the total number of plant species dropped from 21 to 9 (2). Tends to have larger negative effects on predatory species than on small forage fishes. Can also decrease the quantity and quality of recreational activities such as angling, boating, swimming, and waterskiing. It is reasonable to expect that colonization of Eurasian watermilfoil at sites in the Lake Tahoe watershed yield annual damages of at least several hundred thousand to a few million dollars (3).


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. Donaldson, S. 1997. Flood-borne noxious weeds: impacts on riparian areas and wetlands. Proceedings of the California Exotic Pest Plant Council Symposium. 3:7 Available: http://groups.ucanr.org/ceppc/Symposia/
3. Eiswerth, M. E., S. G. Donaldson, and W. S. Johnson. 2000. Potential environmental impacts and economic damages of Eurasian watermilfoil (Myriophyllum spicatum) in western Nevada and northeastern California. Weed Technology. 14:511-518


Question 1.4 Impact on genetic integrity? U Other Published Material

There are three native species of Myriophyllum in California, but no information on hybridization.


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 both areas with natural disturbance, such as river channels, and calmer waters with less disturbance (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 2.2 Local rate of spread with no management? A Other Published Material
Describe rate of spread:

Forms long vines that can grow to four times the original size in one year. Populations in the Tahoe Keys expanded by as much as three times in one year (1).


Sources of information:

1. Donaldson, S. 1997. Flood-borne noxious weeds: impacts on riparian areas and wetlands. Proceedings of the California Exotic Pest Plant Council Symposium. 3:7 Available: http://groups.ucanr.org/ceppc/Symposia/


Question 2.3 Recent trend in total area infested within state? B Observational
Describe trend:

So widespread that it is probably still spreading by not as rapid as in past.


Sources of information:

DiTomaso, observational.


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

Reproduces vegetatively by rhizomes, stem fragments, and axillary buds. Axillary buds detach readily. Male and female flowers develop on the same plant. In California, seed production is much less important than vegetative production. Some populations produce many seeds, but seedlings are rarely observed. Seeds can survive at least seven years under dry conditions. At maturity, fruits detach and float for a period before sinking (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 2.5 Potential for human-caused dispersal? A Other Published Material
Identify dispersal mechanisms:

Escaped from aquaria. Can be spread by dumping of aquarium water or by catching in boat propellers.


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

Can cling to the feet and feathers of waterbirds or be carried downstream by waterflow, especially during winter floods. Waterbirds eat and disperse seeds. Easily fragmented and moved downstream.


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:

Present in almost every U.S. state (1, 2). Typically inhabits temperate regions in the northern hemisphere but can also live in subtopical to tropical areas (2).


Sources of information:

1. USDA, NRCS. 2005. The PLANTS Database, Version 3.5 (http://plants.usda.gov). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.
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.


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

Present in ponds, lakes, rivers, streams, canals, and ditches. Usually in still or slow-moving water but occasionally found in faster-moving water of streams and rivers. Present in the central-western region, San Joaquin Valley, southern Sacramento Valley, and both the California and Nevada sides of Lake Tahoe, to 150m. Inhabits a wide range of environmental conditions. Often grows in hard alkaline water up to 3m deep, but can survive in water up to 8m deep if it is very clear with high light penetration. Tolerates a broad pH range (5.4 - 11), brackish water, and sandy to acid-peat substrates (1).
Where water evaporates slowly and the plants are gradually stranded, Eurasian watermilfoil can develop a land form (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. Anonymous. 2005. Eurasian watermilfoil (Myriophyllum spicatum L.). Written findings of the Washington State Noxious Weed Control Board. Available: http://www.nwcb.wa.gov/weed_info/Written_findings/


Question 3.2 Distribution/Peak frequency? B Observational
Describe distribution:

Probably most common submerged aquatic weed in California. Very widespread.


Sources of information:

DiTomaso, observational.


Worksheet A - Innate reproductive potential

Reaches reproductive maturity in 2 years or less Yes
Dense infestations produce >1,000 viable seed per square meter No
Populations of this species produce seeds every year. Yes
Seed production sustained over 3 or more months within a population annually No
Seeds remain viable in soil for three or more years Yes
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: 8
Total unknowns: 0
Total score: A?

Related traits:

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, reservoirsB, 20% - 50%
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): B

Infested Jepson Regions

Click here for a map of Jepson regions

  • Cascade Range
  • Central West
  • Desert Province
  • Mojave Desert
  • Sonoran Desert
  • Great Valley
  • Modoc Plateau
  • Northwest
  • Sierra Nevada
  • Southwest