Name:
Cabomba (Cabomba Caroliniana)
Description
Cabomba (Cabomba caroliniana) is a perennial aquatic herb with branched stems that have white or reddish brown hairs growing on them. It is fully submerged, except for occasional leaves and flowers that float and later emerge on stalks several centimetres above the water surface.
It roots at the nodes of creeping runners (stolons or rhizomes) and lower stems into the substrate on the bottom of water bodies, and the stems (up to 5 m or even sometimes 10 m long) can reach the surface. Parts of the plant can survive free-floating for 6-8 weeks.
The underwater leaves are arranged in opposite pairs or sometimes in whorls of 3 on the stems. They are circular to kidney-shaped in outline (up to 6 cm wide) and are finely divided into narrow linear segments less than 1 mm wide, which are usually further divided, giving the leaves a feathery fan-like appearance (hence Cabomba being known as Fanwort in some countries). These leaves secrete a sticky mucus or gelatinous slime that covers the submerged parts of the plant. The few (if any) floating leaves are small (up to 2 cm long), not divided, narrowly elliptic or diamond-shaped and borne alternately on the flowering branches. The solitary flowers are about 2 cm wide, and range in colour from white (with a yellow centre) to pale yellow, and may also have a pink to purplish tinge.
For further information and assistance with identification of Cabomba contact the herbarium in your state or territory.
Distribution:
Cabomba is naturalised in widely scattered locations in northern and eastern Australia. Most infestations occur in the hinterlands of northern New South Wales and southern Queensland. However, infestations have been recorded as far apart as Darwin and central Victoria.
In Queensland the heaviest infestations occur in shallow dams on the Sunshine Coast but significant infestations also occur in Far North Queensland (e.g. Atherton Tableland and Cairns region). Cabomba is growing in numerous creeks and river systems on the New South Wales North Coast (e.g. near Murwillumbah) and the Central Coast region, as well as in lakes in central Victoria (e.g. Lake Nagambie and near Foster).
In the Northern Territory, the Marlow Lagoon infestation has been eradicated, and the only known infestation now is in a section of the Darwin River downstream of Darwin River Dam.
Cabomba infestations are isolated and currently affect relatively few water bodies. However, based on climate and the availability of water, it could easily spread further across southern and eastern Australia. Waterways from Cape York to Hobart and from Sydney to Perth are at risk. Additionally, Cabomba could potentially infest the Ord River irrigation system.
Habit:
Aquatic, Herb
Key points:
- Cabomba (Cabom ba caroliniana) is a mostly submerged, feathery-leaved aquatic herb that grows quickly and produces vast amounts of submerged plant material.
- It is still sold as an aquarium plant in some States, which makes control very difficult. Its spread has been assisted by the deliberate ‘seeding’ of waterways to ensure a wild supply for the aquarium trade.
- Weed control in aquatic environments is difficult, and control options are limited by social and environmental considerations.
- Cabomba is sensitive to drying out and requires permanent shallow water. So, where possible, draining a water body can provide temporary control.
How it spreads:
Cabomba does not appear to produce mature, fertile fruit or seed in Australia it reproduces and spreads here by the movement of small plant pieces that readily break off the brittle stems and runners. Fragments may survive in water for 6-8 weeks, and a detached shoot as short as 10 mm with at least one pair of leaves can grow into a mature plant. Fragments can be spread by water flow and possibly by attachment to waterfowl, water craft, and boat trailers, also by disposal of unwanted aquarium plants, as well as being deliberately planted to allow wild cultivation for the aquarium trade.
It is still illegally sold as an aquarium plant in many States of Australia, supplied by both growers and wild harvest operations. The trade represents a $300 000-a-year industry, while conservative 1999 estimates place the national cost of Cabomba control at more than $500 000.
Where it grows:
Cabomba grows in still or slow-moving freshwater, in ponds, lakes, dams, channels and quiet streams. It is sensitive to drying out and requires permanent shallow water, usually less than 3 m, but up to 10 m, deep. It grows well on a silty bed but not so well on hard surfaces. It grows quickly and so can respond to wide fluctuations in water depth.
Cabomba grows well in high nutrient environments with a low pH; in more alkaline waters it tends to lose its leaves. High calcium levels also inhibit growth. 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.
Flower colour:
White
Distribution map:
Impacts:
Cabomba is a Weed of National Significance. It is regarded as one of the worst weeds in Australia because of its invasiveness, potential for spread, and economic and environmental impacts.
Cabomba is choking waterways along Australia’s east coast. Cabomba grows quickly. It can therefore block slow-moving waterways such as irrigation channels, ponds, dams and lakes, and significantly reduce storage capacity by siltation. It also decreases water quality by causing colouring, odours, accumulation of organic matter and stagnation in streams.
Cabomba is an aggressive invader of native freshwater systems, particularly if they are nutrient rich, excluding native plant species by blocking out sunlight and competing for space and nutrients. It can also have a negative impact on native fish, aquatic invertebrates, birds, reptiles and other animals. At the same time, it can create a suitable habitat for mosquito breeding.
Dense infestations of Cabomba degrade the aesthetic value of streams, and impede aquatic transport and recreational activities such as swimming, diving and boating.
Origin:
There are five species of Cabomba, from tropical and warm temperate areas of the Americas (North, Central and South America) and the West Indies. None is native to Australia.
Cabomba is native to eastern USA, southern Brazil, Paraguay, Uruguay and north-eastern Argentina. It has been spread throughout the world by the aquarium trade and is now naturalised, usually from discarded aquarium plants, in many countries, including Australia and New Guinea.
