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Carolina Water-shield
Cabomba caroliniana

Last edited: January 14th 2022

Fanwort

Carolina Water-shield - Cabomba caroliniana

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Short description of Cabomba caroliniana, Carolina Water-shield

Fanwort is a perennial aquatic plant with opposite, dissected submerged leaves, laminar floating leaves and solitary white emergent flowers, resembling plants of Ranunculus subgenus Batrachium although they have three petals and three sepals.

Impact summary: Cabomba caroliniana, Carolina Water-shield

None known.

Habitat summary: Cabomba caroliniana, Carolina Water-shield

The population in the Forth and Clyde Canal was associated with a heated water inflow and died out when this inflow ceased. The population in the Basingstoke Canal is not associated with heated water and occurs with a diverse native flora.

Overview table

Environment Freshwater
Species status Non-Native
Native range Northern America, Brazil, Argentina Distrito Federal, Paraguay, Georgia, Uruguay
Functional type Land plant
Status in England Non-Native
Status in Scotland Non-Native
Status in Wales Non-Native
Location of first record v.c.99
Date of first record 1969

Origin

It is most likely that both GB populations of fanwort involve material from the eastern United States.

First Record

Fanwort was first recorded in the Forth and Clyde Canal in 1971.

Pathway and Method

It was almost certainly introduced by dumping of aquarium contents (the canal also supported goldfish).

Species Status

Fanwort is not spreading rapidly in GB, it is present at single sites in Belgium, Canada, Germany, Hungary and New Zealand and in none of these is it spreading rapidly. In the Netherlands, the plant is present in three locations and has become invasive in one of these, apparently benefiting from high nutrient levels. In Australia it is widespread and invasive. It also occurs as an alien in India, Malaysia, New Guinea and Japan.

Dispersal Mechanisms

There is no evidence that fanwort has successfully spread in GB (beyond local spread in the Basingstoke canal), each known population is likely to have resulted from independent introductions.

Reproduction

Fanwort apparently does not reproduce sexually outside its native range. The stems are fragile and it is able to grow from a single node with one pair of leaves, it can also apparently spread from rhizome fragments. It is likely that any reproduction in Britain is vegetative.

Known Predators/Herbivores

None known outside its native range, in its native range, it is eaten by mammals, wildfowl, a number of species of weevil and noctuid Lepitoptera.

Resistant Stages

None known.

Habitat Occupied in GB

Both populations recorded in GB have been in canals. The population in the Forth and Clyde Canal was associated with an inflow of heated water to the canal, where it occurred with Myriophyllum alterniflorum, in the Basingstoke Canal it occurs with a wide range of aquatic and marginal plants, including Elodea nuttallii, Phalaris arundinacea, Ricciocarpos natans, Sagittaria sagittifolia and Sparganium emersum. It has been suggested that it is dependent upon high nutrient levels and may be out-competed by other species at low nutrient levels.

In GB, fanwort has been recorded from three sites. Between 1969-71 it occurred in the Forth and Clyde Canal, but it died out when a heated water inflow was stopped. It has been known from the Basingstoke Canal since 1990 where it has spread approximately 20km. There is a third unconfirmed record from Connah's Quay (Flintshire) in 2009.

Environmental Impact

Fanwort is highly competitive and can block sunlight to the exclusion of other submerged plants, as well as preventing germination of seed. It can also obstruct movement of animals within water bodies. When dense mats decay this can cause dissolved oxygen depletion killing fish and other aquatic organisms. It has also been shown that fanwort has allelopathic qualities, inhibiting germination and growth in some aquatic species.

Health and Scoial Impact

Decay of dense beds of fanwort can cause foul-smells. Dense growths can impede swimming, boating, fishing and other water-based recreation as well as degrading the aesthetic and scenic qualities of sites.

Economic Impact

There is no evidence of any economic impact of fanwort in GB. In Australia, the trade in aquatic plants represents a $300,000 a year but conservative (1999) estimates place the national cost of fanwort control at more than $500,000. Wild rice production (Zizania palustris L.) in Canada could be affected by fanwort. Dense infestations can degrade aesthetic and scenic qualities of sites, directly influencing tourism and real estate values, as well as obstructing drainage, navigation and water-borne transport, compromise water storage capacity and taint drinking water supplies.

Identification

Lansdown, R.V. (2009) A field guide to the riverine plants of Britain and Ireland. Ardeola, Stroud, Gloucestershire.

Stace, C.D. (2010) New flora of the British Isles. Third Edition. Cambridge University Press, Cambridge.

Biology, ecology, spread, vectors

European and Mediterranean Plant Protection Organization Data sheets on invasive alien plants: 06-12971 Cabomba caroliniana (www.eppo.orgQUARANTINEias_plants.htm). 

Preston, C.D., Croft, J.M. (1997) Aquatic Plants in Britain and Ireland. Harley Books, Colchester.

Management and impact

European and Mediterranean Plant Protection Organization Data sheets on invasive alien plants: 06-12971 Cabomba caroliniana (www.eppo.orgQUARANTINEias_plants.htm).

General

European and Mediterranean Plant Protection Organization Data sheets on invasive alien plants: 06-12971 Cabomba caroliniana (www.eppo.orgQUARANTINEias_plants.htm).

Preston, C.D., Croft, J.M. (1997) Aquatic Plants in Britain and Ireland. Harley Books, Colchester.

Alert status

Carolina Water-shield, Cabomba caroliniana is an Alert Species

Find more information about this alert and the full list of alert species.

Spotted this species?

Find out how to record your sighting.

Legislation

Carolina fanwort, Cabomba caroliniana, is:

  • A Species of Special concern
  • Listed under Schedule 9 of the Wildlife and Countryside Act 1981

Read more about Non-native species legislation.