Cabomba caroliniana A. Gray
Synonyms - Cabomba australis, Cabomba pulcherrima
Cabomba is a native American name for a water plant.
Caroliniana refers to the Carolinas in the USA near where it has naturalised.
Other Names:Fanwort - because it has fan shaped leaves and wort is an old term for weed.
Carolina watershield, fish grass, Washington grass, watershield.
Summary:Cabomba is a perennial fast-growing aquatic herb with stems to 10 m long. The submerged leaves are about 50 mm in diameter and finely dissected with the slender segments spread out in the shape of a fan. The floating leaves are less frequent, narrow and less than 20 mm long. The flowers are white with a yellowish centre, floating, single and about 20 mm in diameter. Each flower has 6 petals which are 5-10 mm long. The plants do not seed in Australia but is spread by plant fragmentation.
Cabomba is native to South America and was brought to Australia as an aquarium plant, now a serious weed of dams, lakes and slow-moving waterways. It flowers mainly in summer.
First leaves:The first few pairs of leaves are narrow and not divided. These are followed by transitional leaves until the typical submerged adult leaf form appears.
1) Submerged leaves
Opposite, arranged in whorls.
Petiole - to 30 mm long.
Blade - Finely dissected to form a fan shape, 30-600 mm wide, covered with a thin coating of jelly. Individual leaves can have up to 200 divisions each.
2) Floating leaves
Alternate. Few or absent. Usually occur at flowering in groups at the tips of the flowering stem.
Petiole - attached to the lower surface of the blade.
Blade - Narrowly elliptical and may be slightly constricted in the middle or forked at one end, entire, 5-20 mm long x 1-3 mm wide.
Stems:Olive green to reddish brown, slender, 2-4 mm thick, oval in cross section and up to 10 m long but usually less than 5 m long. Much branched from near the base. There may be 40 stems originating from a single root mass. They may be covered in jelly. They may have scattered, short, white or reddish-brown hairs. Thicker stems partially buried in the mud may have small opposite leaves. The stems are fragile and break easily. Under the water the stems and their leaves can have a tubular or columnar appearance.
Flower stem - short.
Flower head:The flowers are short lived and emerging from the water for 2 days. They close and recede back into the water over night. Flowers open by mid morning and close by late afternoon. Up to 50 flowers per square metre per day may be produced in dense infestations.
Flowers:Single flowers on short stalks raised 10-40 mm above the surface of the water. Up to 20 mm diameter, white or cream or purplish often with a pink tinge at the tips and two yellow spots on the auricles at the base of each petal. The 3 petals and 3 sepals look similar giving the appearance of 6 alternating petals.
Sepals - 3, oval
Petals - 3, oval
Fruit:2-4 bottle shaped leathery segments, each containing 3 seeds.
Seeds:1.5-3 mm long x 1-1.5 mm wide, dark coloured, oblong, with longitudinal rows of minute wart-like projections. Seeds are slightly wider at one end, with a small cap at the other end and covered in gelatinous mucus. Viable seed has been recorded from the Darwin infestation. Other infestations have produced seed but none of it has germinated.
Roots:Usually rooted in the mud but can survive as a free floating plant for 4-8 weeks.
The shallow fibrous root system is made up of numerous long and slender roots. The roots are initially smooth, white or purplish and unbranched, becoming branched and dark brown or black with age.
Roots can form at any node on stems, without the need for contact with soil. Nodal roots are thin, white and unbranched, and can be up to 240 mm long.
Its shallow, weak root system limits the distribution of the species to slow-moving waters.
Key Characters:Aquatic vine
Finely divided fan shaped leaves in pairs.
White to cream five petalled flowers held just above the water.
Differentiation between Cabomba species is best done on the basis of seed characteristics.
Perennial aquatic herb.
Propagated from cuttings in the spring and summer in the aquarium trade.
Grows during the warm weather and usually dies off with the first frosts in autumn.
Physiology:Prefers nutrient rich water bodies.
Usually restricted to water bodies that are a few centimetres to 5 m deep.
It can survive 6-8 weeks free floating and detached from the bottom mud.
Tolerates low light levels but complete shading can control it.
Reproduction:Stem fragments mainly and seed in Darwin. In other Australian infestations the seed was not viable.
Flowering times:Mainly November to March in Queensland but can be at any time of the year.
They tend to flower all year in tropical climates. In temperate climates flowering often stops over the winter period.
Seed Biology and Germination:Seed germination is usually very variable.
In infestations that produce significant quantities of seed some are expected to last for 2 years.
100% germination at 4 weeks falling to 76% by 4 months has been reported.
Seeds lost viability after 9 hours of desiccation in one study but dried and stored seed had greater viability than moist seeds in another study. A bit more work needs to be done.
Seeds don't float and most remain close to the mother plant.
Seeds are not expected to survive the passage through the gut of birds or animals.
Hybrids:There are several variants in the herbarium trade.
The form that has naturalised in Australia appears to be a hybrid between an Argentinean and American variety of Cabomba caroliniana.
Allelopathy:Extracts are allelopathic, reducing germination of wheat and lettuce and reducing growth of some aquatic species.
Population Dynamics and Dispersal:Long distance dispersal is by dumping of aquarium plants in water bodies and transport on recreational equipment such as boots, nets and traps.
Local dispersal is by production of daughter plants from intact stems or movement of stems fragments. Any stem fragment that includes a node can grow into a new plant. In summer, the buoyant stems keep the tips in a vertical position but in winter they lose buoyancy and drop to the sediment. In the spring, nodes near the tip form roots and a new growing tip. Eventually the connecting stem disintegrates, separating the mother from the daughter plants.
In some areas, such as Darwin, seed may be produced and contribute to spread.
It can be displaced by more aggressive aquatic species such as Egeria densa.
Origin and History:Native to the South American subtropics but has become widely naturalised in North America, southern Asia and Australia. (Schooler and Chan, 2011).
Introduced as an aquarium plant and naturalised in farm dams of northern NSW and coastal rivers of southern Queensland. It has now moved south as far as Melbourne and north to Cape Yorke and Darwin.
The first herbarium record was 1967 but it was probably introduced in the 1930's.
Distribution:NSW, NT, QLD, VIC.
Courtesy Australia's Virtual Herbarium.
Habitats:Ponds, slow moving streams and water depths from 5 cm to 5 m.
Prefers slightly acidic water with a pH of 4-6. More than 4 ppm of calcium inhibits growth.
Climate:Humid to sub humid tropics, temperate areas
Soil:Roots attached to mud on the bottom of dams and streams.
It prefers areas with fine and soft silt sediments, and tends to be less vigorous on sand or stony bases. On clay or sand substrates the thin roots struggle to hold the plants in place.
Plant Associations:Water plants.
Ornamental aquarium plant. Food plant.
Detrimental:Clogs drains, rivers and dams.
Restricts recreational and agricultural activities on water bodies.
Crowds out native aquatic plants.
Control costs in Australia in 2009 were estimated to be $600,000-$800,000 per year.
Weed of National Significance (WONS).
Declared plant in all Australian states and territories.
Management and Control:Physical removal is not very effective because it spreads by stem fragments.
Manipulating water levels to expose and dry the plants has been used effectively.
Drying stems for 24 hours will kill them, however moist masses or stems in moist soil may remain viable for weeks.
Hydrogel gave 50% control of Cabomba in Sydney.
Try 1 L 2,4-D ester 800 (or 1.2 L 2,4-D LV ester680) plus 1 kg diatomaceous earth in 20 litres water and apply to 100 square metres by an under water boom with nozzles at about half the depth of the water. Apply in the warmer months and repeat if regrowth appears.
Diquat has provided around 50% control either alone or when applied with Hydrogel.
Water soluble formulations have generally been less effective than the ester formulations.
Copper sulphate and dichlorprop have been used overseas and provide varying levels of control.
Fluridone has provided the best control in the USA but has failed in a few Australian trials.
Endothal at 5ppm has also given promising results overseas.
99% shade for 3-4 months can provide high levels of control.
Herbicide resistance:None reported.
Biological Control:Chinese grass carp (Ctenopharyngodon idella) and manatees or sea cows (Trichechus spp.) have been used overseas for biocontrol.
Related plants:None in the same genus in Australia.
The current definition of Cabomba caroliniana includes the previously separate species Cabomba australis (creamy white flowers) and Cabomba pulcherrima (purplish or purple-tinged flowers with darker veins), and a number of natural and horticultural varieties.
Brasenia schreberi is native to Australia
Plants of similar appearance:Water Milfoils (Myriophyllum spp.)
Ambulia (Limnophila spp.) has native and introduced species that always have leaves arranged in whorls around the stem. Some leaves are emergent, and these are darker green and broader. The submerged leaves are finely divided and feathery. The flowers are solitary, small, blue, pink or violet in the leaf axils.
Hornwort (Ceratophyllum demersum) is usually free-floating, but it sometimes
takes root loosely in the substrate. The submerged leaves look similar to those of Cabomba as they are dissected and appear feathery, but are always arranged in whorls around the stem. Each leaf is dissected or 'forked' only two to four times, whereas Cabomba has many more dissections per leaf. Fine forward-pointing teeth are also visible with the naked eye along the sides of each leaf division. Hornwort does not produce the masses of emergent flowers that Cabomba does, nor does it have any form of floating leaves. Hornwort is native to mainland Australia.
Egeria, Leafy Elodea or Dense Waterweed (Egeria densa) is often confused with Cabomba when looking at an infestation from a distance. Like Cabomba it has white flowers that are held above the surface of the water. However, the leaves are not dissected and feathery but are entire and up to 4 centimetres long, occurring in whorls of four or five along the stem, and the flowers have only three petals.
Elodea (Elodea canadensis) has leaves that are not dissected and feathery, occurring in whorls of three along the stems. The flowers are very small (5 millimetres in diameter) and inconspicuous. They float in or on the water
surface attached to long, white, thread-like stems.
Hydrilla (Hydrilla verticillata) is a submerged aquatic plant that can look
similar to a Cabomba infestation under the water. The leaves are not feathery (dissected), but they have slightly toothed margins and occur in whorls of three to eight on the stems. Hydrilla is native to mainland Australia.
Brasenia schreberi is native to Australia.
References:Bodkin, F. (1986). Encyclopaedia Botanica. (Angus and Robertson, Australia).
Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra).
Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne).
Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney).
Harden, Gwen J. (1991). Flora of NSW. (Royal Botanic Gardens, Sydney). Volume . P. Diagram.
Lazarides, M. and Cowley, K. and Hohnen, P. (1997). CSIRO handbook of Australian Weeds. (CSIRO, Melbourne). #163.1
Parsons, W.T. and Cuthbertson, E.G. (1992) Noxious weeds of Australia. (Inkata Press, Melbourne). P353-354. Photos.
Randall, J.M. and Marinelli, J. (1996) Invasive Plants. (Brooklyn Botanic Gardens Inc. Brooklyn). P. Photo.
Schooler, S. and Chan, R. (2011). Biological Control and Ecology of Cabomba and Alligator Weed. CSIRO Ecosystem Sciences. RIRDC Publication No 11/029. RIRDC Project No 08-53.
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