Cabomba caroliniana A. Gray

Common Name: Carolina fanwort

Synonyms and Other Names:

Cabomba (Portuguese-Brazil), Carolina water-shield, Fanwort, Fish grass, Green Cabomba, Washington grass, Washington-plant



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Identification: C. caroliniana is fully submerged except for occasional floating leaves and emergent flowers (Australian Department of the Environment and Heritage 2003). The roots grow on the bottom of water bodies and the stems can reach the surface. Parts of the plant can survive free-floating for six to eight weeks.  It is a perennial, growing from short rhizomes with fibrous roots. The branched stems can grow up to 10m long and are scattered with white or reddish-brown hairs.

The underwater leaves are divided into fine branches, resulting in a feathery fan-like appearance. These leaves are about 5cm across and secrete a gelatinous mucous which covers the submerged parts of the plant. The floating leaves, however, are small, diamond-shaped, entire, and borne on the flowering branches. The solitary flowers are less than 2cm across and range in colour from white to pale yellow and may also include a pink or purplish tinge. The flowers emerge on stalks from the tips of the stems (Australian Department of Environment and Heritage, 2003).

Submersed leaves: petiole to 4 cm; leaf blade 1-3.5 × 1.5-5.5 cm, terminal segments 3-200, linear to slightly spatulate, to 1.8 mm wide. Floating leaves: blade 0.6-3 cm × 1-4 mm, margins entire or notched to sagittate at base. Flowers 6-15 mm diam.; sepals white to purplish [yellow] or with purple-tinged margins, 5-12 × 2-7 mm; petals colored as sepals but with proximal, yellow, nectar-bearing auricles, 4-12 × 2-5 mm, apex broadly obtuse or notched; stamens 3-6, mostly 6; pistils 2-4, mostly 3, divergent at maturity; ovules 3. Fruits 4-7 mm. Seeds 1-3, 1.5-3 × 1-1.5 mm, tubercles in 4 longitudinal rows

The submersed leaves of Cabomba caroliniana are similar in form to those of Limnophila (Scrophulariaceae; introduced in southeastern United States). The latter has whorled leaves in contrast to the opposite leaves of Cabomba .


Size: Mature plant size is approximately 12-31 inches or more (30-80 cm or more) and may grow up to 10m long (Wilson et al. 2007).


Native Range: Cabomba caroliniana A. Gray is native to southern Brazil, Paraguay, Uruguay, northeast Argentina, southern and eastern USA.


Great Lakes Nonindigenous Occurrences: This plant has been dispersed throughout the world by the aquarium trade and is naturalized in Peru, China, India, Japan, Malaysia, the south east of the USA and parts of Australia and Canada (USDA-GRIN 2003).  

Great Lakes region:  The first sighting in the Great Lakes drainage was in the Lake Michigan drainage in 1935. Reported from IL, IN, MI, NY, OH, PA and Ontario.

Other US Reports: Ala., Ark., Conn., D.C., Fla., Ga., Ky., La., Md., Mass., Miss., Mo., N.H., N.J., N.C., Okla., Oreg., R.I., S.C., Tenn., Tex., Va


Table 1. Great Lakes region nonindigenous occurrences, the earliest and latest observations in each state/province, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Cabomba caroliniana are found here.

Full list of USGS occurrences

State/ProvinceFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
MI1935202011Clinton; Huron; Kalamazoo; Lake Michigan; Lower Grand; Muskegon; Pere Marquette-White; Shiawassee; St. Joseph; Thornapple; Upper Grand
NY199920143Northeastern Lake Ontario; Oneida; Salmon-Sandy
OH200820202Cuyahoga; Southern Lake Erie

Table last updated 7/23/2024

† Populations may not be currently present.


Ecology: Cabomba is sensitive to drying out and requires permanent shallow water, usually less than 3 meters (but up to 10 meters) deep (Australian Department of the Environment and Heritage 2003). It grows rooted in the mud of stagnant to slow flowing water including streams, and smaller rivers (The Washington State Department of Ecology, 2003). It also grows in ponds, lakes, reservoirs, sloughs, ditches, and canals.

It can respond to wide fluctuations in water depths and is a water column feeder that grows well in silty substrate and exhibits reduced vigour in hard substrates. Growth of 50mm a day has been reported in Lake Macdonald in Queensland, Australia. It grows well in high nutrient environments with low pH, but in more alkaline waters it tends to lose its leaves. High calcium levels inhibit growth and unlike other aquatic weeds, cabomba can grow well in turbid water. It prefers a warm, humid climate with a temperature range of 13-27ºC but can survive when the surface of the water body is frozen (Australian Department of Environment and Heritage 2003). PH ranges 4.8~7.8, dCH soft ~ hard.

C. caroliniana flowers from May to September. In the southeastern U.S., C. caroliniana is self-pollinating and seeds readily germinate (The Washington State Department of Ecology 2003).


Means of Introduction: 1935, release from aquarium in Lake Michigan drainage (U.S. EPA 2008). Fanwort stems become brittle in late summer, which causes the plant to break apart, facilitating its distribution and invasion of new waterbodies. It produces seed but vegetative reproduction seems to be its main vehicle for spreading to new waters. Large numbers of plants are sent from Florida to the rest of the U.S. for commercial use. Fanwort is also grown commercially in Asia for export to Europe and other parts of the world. Small-scale, local cultivation occurs in some area and aquarists (aquarium release or escape) are probably responsible for some introductions.


Status: Established, widely distributed in many US states.


Great Lakes Impacts:
Summary of species impacts derived from literature review. Click on an icon to find out more...

EnvironmentalSocioeconomicBeneficial



Cabomba caroliniana has a moderate environmental impact in the Great Lakes.
Realized:
Cabomba caroliniana is an extremely persistent and competitive plant, growing quickly and crowding out other vegetation (WI DNR 2012, Wilson et al. 2007). Populations of C. caroliniana readily form dense mats that block sunlight penetration to lower water depths and shade out germinating seeds or propagules (ENSR International 2005, Forest Health Staff 2006 Wilson et al. 2007).

Cabomba caroliniana has formed monocultures in Kasshabog Lake, Ontario (Hosgsden et al. 2007 Wilson et al. 2007). The main difference between native macrophyte beds and beds of C. caroliniana in this location is significantly reduced light penetration (Hogsden et al. 2007).

Dense stands of C. caroliniana disrupts fish habitat and replaces native foods sources; which can alter predator/prey relationships among the fish populations (ENSR International 2005, OISAP 2005, PA DCNR 2011, Program 2013).

Large infestations can affect the oxygen concentrations, pH, and organic content of the nearby water and soil (ENSR International 2005, PADCNR 2011). Furthermore, dieback and decomposition could alter nutrient cycling, potentially reducing dissolved oxygen levels and increasing manganese levels (Wilson et al. 2007).

Potential:
After an analysis of invasive species by the U.S. Army Corps of Engineers, the predicted expansion of C. caroliniana was so extensive that this species could pose a severe threat to ecosystems in Minnesota (Madsen 1999).  Warmer winter temperatures and lower water levels may aide in the continued northward expansion of C. caroliniana (Hudon and Carignan 2008).

Cabomba caroliniana mats can trap detritus and increase sedimentation which could alter the hydrology or even clog freshwater streams and drainage canals (ENSR International 2005, Forest Health Staff 2006, U.S. EPA 2008). 

Morrison and Hay (2011) found that in response to direct feeding activity, C. caroliniana is capable of inducing a chemical defense to suppress herbivory.  Cabomba caroliniana extracts also inhibited growth of 5 different microbes by 20-90%, suggesting that C. caroliniana has an anti-microbial defense at feeding scar sites (Morrison and Hay 2011). Due to its ability to induce a chemical defense, the establishment of C. caroliniana could have implications for herbivore fitness and trophic interactions, as well as important microbial activities (Morrison and Hay 2011).

Cabomba caroliniana has a moderate socio-economic impact in the Great Lakes.
Realized:
Cabomba caroliniana's dense mass of underwater leaves and stems provide a tangling hazard for swimmers, boats, fishing lines, and other recreational water users (Ensbey and Oosterhout 2010, Schooler et al. 2006, Wilson et al. 2007). Infestations of this species can cause the water to become stagnant will can cause it to become dark and foul-smelling; ultimately reducing the aesthetic value (Ensbey and Oosterhout 2010). Limitations on water uses can negatively impact real estate values (ENSR International 2005).

Dense mats of C. caroliniana clog streams, drainage canals, and drinking water intakes and interferes with agricultural water uses (WI DNR 2012). Cabomba caroliniana is capable of significantly reducing water storage capacity and tainting/discoloring drinking water supplies, potentially increasing water treatment costs (Lui et al. 2010).

At Kasshabog Lake, Ontario, C. caroliniana has become a nuisance for residents and recreational users, discouraging swimming and boating and reportedly affecting the aesthetic value of shoreline property (Wilson et al. 2007).  

Potential:
If C. caroliniana spreads from Kasshabog Lake to the Trent-Severn Waterway and Great Lakes system, power generation, aquaculture, and other water-based industries could be impacted (Wilson et al. 2007). For instance, Wilson et al. (2007) predicted that C. caroliniana establishment could be detrimental to Canadian populations of wild rice (Zizania palustris L.), a commercially important plant with similar ecological requirements to C. caroliniana.

An estimated $500,000 a year was spent on control of C. caroliniana in Australia as of 2003 (ADEH 2003, Schooler et al. 2006).

Current research on the beneficial effects of Cabomba caroliniana in the Great Lakes is inadequate to support proper assessment.
Realized:
Because of its attractive appearance and its ability to grow quickly, C. caroliniana has been a commercially-important plant in the aquarium trade worldwide (Wilson et al. 2007). Rixon et al. (2005) documented its presence in 20% of investigated aquarium stores in the Great Lakes region, while Cohen et al. (2007) reported C. caroliniana as one of the top 10 plants in the Montreal aquarium trade. Additionally, C. caroliniana was one of the most popular aquatic plants among surveyed aquarium owners in Canada (Marson et al. 2009). However, C. caroliniana is also restricted or prohibited in some Great Lakes states (GLPANS 2008).

While the composition of algae and macroinvertebrate communities were similar between native macrophyte and C. caroliniana beds in Kasshabog Lake, both were more abundant in C. caroliniana beds, potentially because its growth morphology provided more favorable structure for habitat (Hogsden et al. 2007).

Potential:
Relative to native macrophytes, its ecological value as a source of food or habitat for wildlife is unclear (Wilson et al. 2007). However, in some instances C. caroliniana may provide cover for macroinvertbrates and spawning ground for fish (Hamel 2013, Tilt 2013).

Cabomba caroliniana is capable of sequestering lead and may be useful in reclamation efforts (Mikulyuk and Nault 2011).

Preliminary research indicated that C. caroliniana plant matter that is mechanically harvested for control purposes could be anaerobically digested to produce and harness methane-rich gas for energy purposes (O'Sullivan et al. 2010).


Management: Regulations (pertaining to the Great Lakes)
Prohibited in Wisconsin, Illinois and Michigan (GLPANS 2008). In Minnesota, C. caroliniana can be possessed, sold, bought, and transported, but it is illegal to release it into the environment  (MN DNR 2013b). The New York Invasive Species Council ranks this species as posing a high ecological threat (NYISC 2010).

The Great Lakes Life & Wildlife Commission have not found C. caroliniana in their ceded territories, but recommended immediate control upon detection (Falck and Garske 2003).

Cabomba caroliniana is restricted in Ontario (regulatory amendments to Ontario Regulation 354/16 under the Invasive Species Act, 2015).

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

Control
Biological
When fed on my crayfish and snails, C. caroliniana induces a chemical defense mechanism deter both herbivores and microbes that typically attack plants via openings left by herbivores (Morrison and Hay 2011).

Grass carp, Ctenopharyngodon idella, will eat C. caroliniana, but it is not their preferred food source.  Diploid (fertile) grass carp are illegal for use in some states, such as Minnesota (MN DNR 2013a). The use of certified triploid (sterile) grass carp is allowed is New York and Pennsylvania, with the correct permits (NY DEC 2013, Shiels and Hartle n.d.)

Chemical defense also indicates that the use of biocontrol agents on invasive populations of C. caroliniana may not be a viable approach (Morrison and Hay 2011).

Physical
Cabomba caroliniana becomes brittle late in the growing season. Physical control efforts should not be tried during this time because broken pieces can develop into new plants (IISCTC 2007).

Physical cutting and removal of C. caroliniana is most effective on large infestations in closed water bodies (ADEH 2003). In areas of sufficient size and depth, this can be done with floating mechanical (CSIRO Entomology 2011). However, given the low probability of removing every plant fragment, this method is likely to only provide nuisance relief for a few weeks (ADEH 2003). Efficacy can be improved by using tools such as a venturi dredge, which acts like a vacuum cleaner to C. caroliniana fanwort fragments and the root ball (WI DNR 2012). 

Water-level drawdowns have reduced growth of C. caroliniana populations in some areas in southern Wisconsin (WI DNR 2012). Extreme drying, in which the root ball dries completely, is needed or the plant will return (Forest Health Staff 2006, IISCTC 2007).

Ensuring wash-downs of boats, trailers, and other equipment can reduce the spread of Carolina fanwort
(IISCTC 2007).

Chemical
Precise application of appropriate herbicides to submerged C. caroliniana can be problematic and should be done with great care to avoid desired species (ADEH 2003).

Herbicides containing endothall or fluridone have been effective in controlling C. caroliniana (ADEH 2003, Forest Health Staff 2006). Carolina fanwort has also been reported to be sensitive to 2,4-D (Wilson et al. 1997).

In laboratory tests, the application of diquat and flumioxazin (separately) resulted in a greater than 50% reduction in photosynthesis of C. caroliniana, however, these herbicides has not been tested in the field (Bultemeier et al. 2009).

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.


Remarks: In parts of the southeastern United States, plants with purple-tinted flowers, possibly a response to some environmental factor, have been treated as Cabomba caroliniana var. pulcherrima. South American plants with yellow flowers have been called C . caroliniana var. flavida O/rgaard.


References (click for full reference list)


Other Resources:
USGS/NAS Technical Species Profile

USDA/NRCS PLANTS Database

Flora of North America.  2008.  efloras.org

For more detailed control information, please view this Rapid Response Guide from the Massachusetts Department of Conservation and Recreation: http://www.mass.gov/dcr/watersupply/lakepond/downloads/rrp/fanwort.pdf

For more information on grass carp, please visit:
Department of Ecology, State of Washington
http://www.ecy.wa.gov/programs/wq/plants/management/aqua024.html

Michael Porter’s article Controlling Aquatic Vegetation with Grass Carp
http://www.noble.org/ag/wildlife/grasscarp/


US Fish and Wildlife Service Ecological Risk Screening Summary for Cabomba caroliniana


Author: Larson, J. L. Cao, L. Berent, and S. Iott


Contributing Agencies:
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Revision Date: 1/24/2024


Citation for this information:
Larson, J. L. Cao, L. Berent, and S. Iott, 2024, Cabomba caroliniana A. Gray: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI, https://nas.er.usgs.gov/queries/greatlakes/FactSheet.aspx?Species_ID=231&Potential=N&Type=0, Revision Date: 1/24/2024, Access Date: 7/23/2024

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.