Plant Assessment Form

Hydrilla verticillata

Synonyms: Hottonia serrata, Hydrilla angustifolia, Hydrilla dentata, Hydrilla lithuanica, Hydrilla ovalifolia, Hydrilla wightii, Leptanthes verticillatus, Serpicula verticillata, Vallisneria verticillata, Elodea verticillata

Common Names: hydrilla; water thyme; Florida elodea

Evaluated on: 2/15/05

List committee review date: 08/07/2005

Re-evaluation date:

Evaluator(s)

Gina Skurka
CDFA/Cal-IPC
Joseph DiTomaso
(916) 654-0768
gmskurka@cal-ipc.org
University of California-Davis
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 Reviewed Scientific Publication
Impact?
Four-part score AABD Total Score
A
1.2 ?Impact on plant community A. Severe Other Published Material
1.3 ?Impact on higher trophic levels B. Moderate 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
15 Total Score B
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 D. Declining Other Published Material
2.4 ?Innate reproductive potential
(see Worksheet A)
B. Moderate Reviewed Scientific Publication
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 C
3.2 ?Distribution/Peak frequency
(see Worksheet C)
D. Very low Other Published Material

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 Reviewed Scientific Publication
Identify ecosystem processes impacted:

Hydrilla forms large mats that fill the water column and can block or severely restrict water flow. Physical blockage degrades water quality, and slows water flow in canals, thereby increasing sedimentation rates, decreased dissolved oxygen, imparing irrigation and drainage, and clogging pipes, dam trash rakes and machinery. Dense mats alter water quality by raising pH, decreasing oxygen under the mats, and increasing temperature. Also significantly block light penetration into water column. Moderate alteration of ecosystem processes, not irreversibly altering nutrient and mineral dynamics and light availability.


Sources of information:

Bossard, C.C., J.M. Randall and M.C. Hoshovsky. 2000. Invasive Plants of California's Wildlands. Pgs 218-221.
Hydrilla. Technical Information about Hydrilla. 1999. http://www.wa.gov/ecology/wq/plants/weeds/aqua001.html.
Langeland, K.A. 1996. Hydrilla verticillata (L.F.) Royle (Hydrocharitaceae), "The Perfect Aquatic Weed." Castanea 61:293-304.


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

Physical blockage displaces native aquatic vegetation by forming dense stands or large subsurface mats. Dense canopies can often shade out native vegetation. Hydrilla can grow at lower light intensities than many other plants, absorb carbon from water more efficiently thanother plants and can continue to thrive during the summer when carbon can become limiting, store extra P, tolerant of a wide range of water conditions, will thrive in flowing and still water, and tolerate salinity of up to 10 ppt, encroaching upon outer limits of estuaries. Severe alteration of plant community composition, structure and interactions when forms dense stands >75% cover dominated by the species, covering water surface and eliminating or degrading layers below, and significantly reduicing or extirpating populations of native species.


Sources of information:

Bossard, C.C., J.M. Randall and M.C. Hoshovsky. 2000. Invasive Plants of California's Wildlands. Pgs 218-221.
DiTomaso, J. and E. Healy. Aquatic and Riparian Weeds of the West. Hydrilla.
Hydrilla. Technical Information about Hydrilla. 1999. http://www.wa.gov/ecology/wq/plants/weeds/aqua001.html.
Langeland, K.A. 1996. Hydrilla verticillata (L.F.) Royle (Hydrocharitaceae), "The Perfect Aquatic Weed." Castanea 61:293-304.


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

Physical blockage decreases habitat for fish and other wildlife. Reduces use of lakes and waterways for fishing, swimming, boating, water skiing and other recreational activities. Extensive monospecific stands of hydrilla can provide poor habitat for fish and other wildlife, although hydrilla is eaten by waterfowl and it is considered an important food source by biologists. While dense vegetation may contain large numbers of fish, density levels obtained by hydrilla may support few or no harvestable-sized sport fishes. Stagnant water created by hydrilla mats provides good breeding grounds for mosquitoes. In dense populations, moderate reduction in habitat quality for native speices, and privides food for waterfowl. Moderate alteration of higher trophic level populations, communities or interactions.


Sources of information:

Bossard, C.C., J.M. Randall and M.C. Hoshovsky. 2000. Invasive Plants of California's Wildlands. Pgs 218-221.
DiTomaso, J. and E. Healy. Aquatic and Riparian Weeds of the West. Hydrilla.
Hydrilla. Technical Information about Hydrilla. 1999. http://www.wa.gov/ecology/wq/plants/weeds/aqua001.html.
Langeland, K.A. 1996. Hydrilla verticillata (L.F.) Royle (Hydrocharitaceae), "The Perfect Aquatic Weed." Castanea 61:293-304.
Hench, J.E., R. Gibbs, and J.S. Hench. Some Observations on Hydrilla and Wintering Waterfowl in Montgomery County, Maryland. The Maryland Naturalist 38(1-2): 3-9.


Question 1.4 Impact on genetic integrity? D Other Published Material

No native hydrilla in California and and rarely does it reproduce sexually.


Sources of information:

Hickman. 1993. The Jepson Manual.


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

Can readily establish in undisturbed aquatic systems.


Sources of information:

Bossard, C.C., J.M. Randall and M.C. Hoshovsky. 2000. Invasive Plants of California's Wildlands. Pgs 218-221.
DiTomaso, J. and E. Healy. Aquatic and Riparian Weeds of the West. Hydrilla.


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

Introduced in 1976, by 1986 hydrilla had infested over 600 miles of canals, drians, and laterals in the Imperial Irrigation District. The monoecious biotype of hydrilla became established in the Potomac River in 1981 and covered 3600 acres by 1985. Increases rapidly, doubling in less than 10 years.


Sources of information:

Leavitt, J.R., P. Akers, F. Hrusa, and C. Albrecht, CDFA. Target: Hydrilla. Noxious Times, Fall 2001 Pg. 4-6.
Information about hydrilla. http://www.nwcb.wa.gov/weed_info/hydrilla.html. Accessed 1/10/2005.


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

As of 2000, active populations found in 7 counties. Many populations have been eradicated through activity of CDFA.


Sources of information:

CDFA Hydrilla Program Annual Progress Report for 1999 and 2000.


Question 2.4 Innate reproductive potential? B Reviewed Scientific Publication
Describe key reproductive characteristics:

.
Bossard, C.C., J.M. Randall and M.C. Hoshovsky. 2000. Invasive Plants of California's Wildlands. Pgs 218-221.
DiTomaso, J. and E. Healy. Aquatic and Riparian Weeds of the West. Hydrilla.
Netherland, M.D. 1997. Turion Ecology of Hydrilla. J. Aquat. Plant Manage. 35: 1-10.
Hydrilla. Technical Information about Hydrilla. 1999. http://www.wa.gov/ecology/wq/plants/weeds/aqua001.html.
Langeland, K.A. 1996. Hydrilla verticillata (L.F.) Royle (Hydrocharitaceae), "The Perfect Aquatic Weed." Castanea 61:293-304.


Sources of information:

Introduced into North America by the aquarium trade. Hydrilla's vegetative parts disperse with human activities, such as boating and fishing. Several members of the family are popular with the aquarium and nursery industry because they are hardy, tolerant plants and consequently are introduced into water ways. Monoecious hydrilla came in to CA as a contaminant in waterlily shipments. High - there are numerous opportunities for dispersal to new areas, including commercial sales, presence as a contaminant , spread along transportation corridors, and transport on boats.


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

Introduced into North America by the aquarium trade. Hydrilla's vegetative parts disperse with human activities, such as boating and fishing. Several members of the family are popular with the aquarium and nursery industry because they are hardy, tolerant plants and consequently are introduced into water ways. Monoecious hydrilla came in to CA as a contaminant in waterlily shipments. High - there are numerous opportunities for dispersal to new areas, including commercial sales, presence as a contaminant , spread along transportation corridors, and transport on boats.


Sources of information:

DiTomaso, J. and E. Healy. Aquatic and Riparian Weeds of the West. Hydrilla.
Hydrilla. Technical Information about Hydrilla. 1999. http://www.wa.gov/ecology/wq/plants/weeds/aqua001.html.
Langeland, K.A. 1996. Hydrilla verticillata (L.F.) Royle (Hydrocharitaceae), "The Perfect Aquatic Weed." Castanea 61:293-304.


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

Vegetative parts disperse with flooding and can survive ingestion and regurgitation by waterfowl. Frequent long-distance dispersal by animals or abiotic mechanisms.


Sources of information:

DiTomaso, J. and E. Healy. Aquatic and Riparian Weeds of the West. Hydrilla.
Langeland, K.A. 1996. Hydrilla verticillata (L.F.) Royle (Hydrocharitaceae), "The Perfect Aquatic Weed." Castanea 61:293-304.


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

Similar sites occupied in other parts of US and around world.


Sources of information:

Bossard, C.C., J.M. Randall and M.C. Hoshovsky. 2000. Invasive Plants of California's Wildlands. Pgs 218-221.
DiTomaso, J. and E. Healy. Aquatic and Riparian Weeds of the West. Hydrilla.


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

Hydrilla is capable of infesting any freshwater aquatic system in California. It has been observed in the Mojave and Colorado deserts, south and central coasts, San Francisco Bay Area, and Central VAlley. Currently(2000), isolated infestations of hydrilla are found in Shasta, Yuba, Lake, Calaveras, Madera, Mariposa, and Imperial counties. First found in Yuba County in fall 1976.


Sources of information:

Bossard, C.C., J.M. Randall and M.C. Hoshovsky. 2000. Invasive Plants of California's Wildlands. Pgs 218-221.
CDFA Hydrilla Program: Annual Progress Report for 1999 and 2000.


Question 3.2 Distribution/Peak frequency? D Other Published Material
Describe distribution:

California in the eastern North Coast Ranges (Clear Lake area, Lake Co.), Cascade Range (Shasta Lake area, Shasta Co.), north and central Sierra Nevada foothills (northwestern Yuba, central and northwestern Calaveras, southwestern Amador, north eastern San Joaquin, and central and northwestern Tulare Cos.), and Sonoran Desert (Imperial Valley, Imperial Co.), to 200m.


Sources of information:

DiTomaso, J. and E. Healy. Aquatic and Riparian Weeds of the West. Hydrilla.


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. No
Seed production sustained over 3 or more months within a population annually No
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: 5
Total unknowns: 0
Total score: B?

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, 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

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