Lagarosiphon is a perennial, aquatic plant that can dominate freshwater lakes, dams and slow-moving streams. It can grow from the bottom of a water body to the surface (up to a depth of to 6.5 m in clear water or 1 m in murky water) and form dense mats several metres thick at or just below the water surface. The mats displace native vegetation and stop light penetrating the water. It is known as an ‘oxygen plant’ for aquariums however dense infestations consume more oxygen than they produce. They reduce water quality and oxygen levels and have a negative impact on native aquatic animals.
Lagarosiphon is a threat to biodiversity and has the potential to cause serious environmental damage. Infestations choke waterways and reduce the potential for recreational use (e.g. swimming, fishing, boating) and commercial use (e.g. blocking intakes in hydro-electric systems, irrigation systems and outboard motors). As with other submerged aquatic weeds, infestations are extremely difficult to control.
Lagarosiphon is a native of southern Africa. It has spread throughout the world as an aquarium plant and it is a naturalised weed in England, the Channel Islands, northern France and Italy. It is a major water weed in both the north and south islands of New Zealand. Small fragments of this plant are frequently transported on boats and trailers and infestations are often first recorded at boat ramps.
During the late 1970s, lagarosiphon was found and eradicated from a few small dams near Melbourne and Newcastle. These infestations were believed to have originated from ornamental plants in aquariums or ponds. It has also been found in a Sydney aquarium and was intercepted entering Tasmania. A cultivated specimen was recorded in Queensland in 1990. Currently there are no known infestations in New South Wales (NSW).
Lagarosiphon spread in Australia has occurred by vegetative reproduction. Plant fragments break off and roots grow from the nodes (joints between the segments on the stem). It can move large distances downstream. It has not been known to produce male flowers, fruit or seed in Australia or outside its native range.
It is important to accurately identify lagarosiphon. It can be confused with other aquatic weeds, including Elodea canadensis, Egeria densa and Hydrilla verticillata. Unlike lagarosiphon whose leaves occur in alternate spirals along the stem, these three weeds have leaves that are clustered around the stem in whorls. Lagarosiphon has a thread-like root system which branches from the stem, anchoring plants to the bottom. Rhizomes (horizontal stems) are found in the sediment and also anchor the plant.
Key identification features
Lagarosiphon is found in high mountain streams and ponds. It grows best in clear, still or slow-moving fresh water with silty or sandy bottoms and in the cooler waters of the temperate zone (20°C–23°C with a maximum of 25°C). It prefers sheltered areas with high light intensity, and can tolerate high and low nutrient levels and alkaline pH.
Adapted by AnDi Communications from the CRC for Australian Weed Management Weed Management Guide: Lagarosiphon.
Reviewed by Rod Ensbey; Edited by Elissa van Oosterhout
Your local council weeds officer will assist with identification and information on control, removal and eradication of this weed. Infestations can be spread by inappropriate control activities.
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State Prohibited Weed
The plant must be eradicated from the land and that land must be kept free of the plant