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Cabomba

cabomba leaves

Cabomba plant

Cabomba flowers

Hornwort Ceratophyllum demersum

Egeria densa flower1

Egeria densa flower2

Ottelia ovalifolia

Blunt pondweed

Myriophyllum, native

Native Myriophyllum closeup

Parrots feather (R) & native Myriophyllum

Parrots feather & salvinia



family

Cabombaceae

status

Cabomba (Cabomba caroliniana) is listed as noxious in Class 5 throughout NSW. It cannot be sold or propagated or knowingly distributed. It is also listed as a Weed of National Significance.

Description

Cabomba grows attached to the bottom with the long stems floating in the water column and leaves mostly fully submerged below the water surface, in opposite pairs or whorls. Each submerged leaf is distinctively fan-shaped (finely divided with numerous narrow lobes) when seen floating in the water. Flowers are white, 6-petalled and 1-2cm across. They are held above the water surface, possibly together with a few simple (undivided) small narrow emergent leaves.

preferred habitat and impacts


Fresh water bodies such as farm dams, lagoons on river floodplains, rivers and creeks. Still or slow flowing water is usually preferred. Cabomba grows in water up to 3m deep, and can survive if detached from the bottom.
Infestations can become dominant in still waters, crowding out native water plants. It can interfere with human access for swimming and boating, reduce water quality and block pumps.

dispersal


Dumping of aquarium or ornamental pond plants is often the means of spread for aquatic weeds. However, many aquatic species have sticky seed which can adhere to the feathers or feet of water birds, and hence be spread long distances. Many will spread from broken-off pieces or whole plants being moved on boats or fishing equipment from an infested to a clean water body.

look-alikes


Identifying aquatic weeds is difficult. There are many native look-alikes. Get suspicious plants identified by a specialist. Many native water plants will increase in a weedy way if the nutrient level in the water body is increased or the temperature raised. This may not be undesirable, since these plants will use up nutrients which might otherwise feed a toxic blue-green algae bloom.

Cabomba has numerous native and some weedy look-alikes. The fan-like leaves of cabomba are fairly distinctive (see first 2 photos), but need to be placed in a vessel of water so that they can float freely to be seen properly. They could be confused with the native hornwort (Ceratophyllum demersum), which has inconspicuous flowers and horned fruits.  Its leaves are also in whorls but are divided into fewer segments than those of cabomba.

Dense waterweed or leafy elodea (Egeria densa) has similar white flowers held above the water surface, but its leaves are simple and undivided, in whorls of 3-8 and the flowers have only 3 petals. It is also a noxious weed in class 4 throughout NSW (cannot legally be sold). Several other aquatic plants have a similar habit and simple undivided leaves in whorls (the weeds Lagarosiphon major and Canadian pondweed (Elodea canadensis) and the native Hydrilla verticillata). The native swamp lily (Ottelia ovalifolia) has similar white flowers which sit at the water surface, but the flowers are 3-petalled and its leaves, which also sit on the surface, are quite large (to about 15cm long), oval and waterlily-like.

The native pondweeds (Potamogeton species) also have long trailing submerged stems, but their leaves are simple and arranged in opposite pairs or alternately along the stems. Their small spikes of
inconspicuous flowers are held just above the water surface in summer.
Blunt pondweed (Potamogeton ochreatus) is illustrated.

Native species of water milfoil (Myriophyllum species) are very similar in habit, but their leaves are either simple or finely lobed (but not fan-shaped) and often arranged in whorls of 3-6 around the stems. Their flowers are tiny, red and clustered in the leaf axils. There is also an introduced water milfoil, parrot’s feather (Myriophyllum aquaticum - see final 2 photos, the first of which shows parrot's feather on the right and a native Myriophyllum on the left, and the last shows parrot's feather with salvinia, another noxious aquatic weed).  

control

Most importantly, do not dump unwanted aquatic plants into water bodies, or grow species with weed potential in ponds or aquaria. Some invasive water plants are still sometimes sold by nurseries or pet shops. If you notice this, report the instance to Council, so that the proprietors can be advised that it is illegal to sell these plants.
Once an infestation is established, and has been definitely identified, there are two options, mechanical or chemical control. Chemical control is difficult for a plant which is growing almost entirely below the water surface. If you suspect you have an outbreak of an aquatic weed, notify your local weed control authority (usually Council) and take their advice on control methods.