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Scientific Name
Synonyms
Family
Common Names
Origin
Cultivation
Naturalised Distribution
Habitat
Habit
Distinguishing Features
Stems and Leaves
Flowers and Fruit
Reproduction and Dispersal
Environmental Impact
Other Impacts
Legislation
Management
Similar Species
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infestation (Photo: Trevor James)

habit (Photo: Trevor James)

reflexed leaves (Photo: Trevor James)

Lagarosiphon major

Scientific Name

Lagarosiphon major (Ridl.) Moss

Synonyms

Elodea crispa hort. ex Henkel
Lagarosiphon muscoides Harv. var. major Ridl.

Family

Hydrocharitaceae

Common Names

African oxygen weed, African elodea, coarse oxygen weed, curly water thyme, lagarosiphon, oxygen plant, oxygen weed, oxygen-weed, South African oxygen weed

Origin

Native to central and southern Africa (i.e. Zambia, Zimbabwe, Botswana, Lesotho and South Africa).

Cultivation

Lagarosiphon (Lagarosiphon major) has been cultivated in Australia as an aquarium plant, but is no longer known to be deliberately cultivated.

Naturalised Distribution

Naturalised in the coastal districts of northern New South Wales and sparingly naturalised in Tasmania. Small infestations reported near Melbourne, in Victoria, and Newcastle, in New South Wales, were eradicated in the late 1970s.

Possibly also naturalised in Victoria and naturalised overseas in Europe (e.g. the UK, Austria, France, Germany, Italy, Portugal, Spain and Switzerland), New Zealand and the Mascarenes (e.g. La Réunion).

Habitat

A potential weed of slow-moving waterways, ponds, lakes and dams in the temperate regions of Australia.

Habit

A submerged, long-lived (i.e. perennial), freshwater plant with stems that are usually rooted to the substrate. It also produces creeping underground stems (i.e. rhizomes).

Distinguishing Features

Stems and Leaves

The fragile stems are much-branched, slender (3-5 mm thick), and up to 5 m long. They are produced off the creeping underground stems (i.e. rhizomes) and grow up towards the water surface. The stem joints (i.e. nodes) and leaves are wider apart near the base of the stems but become more crowded towards their tips. Roots (i.e. adventitious roots) are produced from near the base of these stems, at their lowermost joints (i.e. nodes).

The elongated and strap-like leaves are alternately arranged along the stems in a distinctive spiralling pattern. These leaves (5-20 mm long and 2-3 mm wide) are stalkless (i.e. sessile) and are densely clustered towards the tips of the branches. They are strongly curved downwards (i.e. reflexed) and have minute teeth along their margins.

Flowers and Fruit

Separate male and female flowers are produced on separate plants (i.e. they are dioecious), and only female plants are found in Australia. Both types of flowers are small (less than 3 mm across) and borne in the upper leaf forks (i.e. axils). The female flowers are borne singly on a long thread-like stalk (i.e. filamentous hypanthium). They are pink or purplish in colour and have six minute 'petals' (i.e. perianth lobes or tepals). Flowering occurs mostly during summer and early autumn.

As male plants are not present in Australia, fruit and seeds are not produced here.

Reproduction and Dispersal

All reproduction is vegetative (i.e. asexual) in Australia, via stem fragments and creeping underground stems (i.e. rhizomes).

The creeping underground stems (i.e. rhizomes) allow colonies of this weed to increase in size and spread laterally across or along a water body. Stem fragments are usually introduced into new water bodies in dumped aquarium waste are spread down catchments by water movement and floods.

Environmental Impact

Lagarosiphon (Lagarosiphon major) is regarded as an emerging environmental weed in Tasmania, and as a potential environmental weed or "sleeper weed" in many parts of southern Australia. It is also on the "Alert List for Environmental Weeds", a list of 28 non-native plants that have the potential to seriously degrade Australia's ecosystems which are currently in the early stages of establishment.

Lagarosiphon (Lagarosiphon major) grows extremely quickly from the bottom waterbodies and forms dense mats of vegetation several metres thick at or just below the water surface. It will withstand low light levels, and can grow in water more than 6 m deep. Its canopy spreads out across the upper levels of a waterbody, thereby shading out and out-competing other underwater species. Lagarosiphon (Lagarosiphon major ) can dominate freshwater lakes, dams and slow-moving streams and has the potential to become a troublesome weed of such habitats throughout the temperate and sub-tropical regions of Australia.

Dense infestations are generally produced in nutrient-enriched waters. Such infestations can block light penetration, out-competing and displacing native water plants and affecting associated populations of aquatic invertebrates. They can also deplete oxygen levels in the water, thereby making waterbodies less habitable by native fish and waterbirds.

Lagarosiphon (Lagarosiphon major) is a significant problem weed in New Zealand, where it completely dominates waterbodies, preventing their use for recreational activities such as swimming, boating and fishing. It has an early competitive advantage which allows it to successfully out-compete native species such as milfoils (Myriophyllum spp.) and pondweeds (Potamogeton spp.). Lagarosiphon (Lagarosiphon major) is also well established in the UK, where it has displaced other introduced waterweeds in recent years including elodea (Elodea canadensis) and Nuttall’s pondweed (Elodea nuttallii).

Other Impacts

Lagarosiphon (Lagarosiphon major) can impede the passage of boats on infested waterways and can interfere with recreational activities like swimming and fishing. Dense infestations can also increase the impact of flooding and can interefere with electricity generation in hydro-electric power plants. For example, in 1968, lagarosiphon (Lagarosiphon major) caused a power outage when it blocked the intake screens at the Aratiatia hydro-electric power station in New Zealand.

Legislation

This species is declared under legislation in the following states and territories:

Management

For information on the management of this species see the following resources:

Similar Species

Lagarosiphon (Lagarosiphon major) can be confused with other submerged water weeds such as dense waterweed (Egeria densa), elodea (Elodea canadensis), hydrilla (Hydrilla verticillata), hornwort (Ceratophyllum demersum), cabomba (Cabomba caroliniana) and parrot's feather (Myriophyllum aquaticum). Hydrilla (Hydrilla verticillata) and hornwort (Ceratophyllum demersum) are native to large parts of Australia. These species can be differentiated by the following differences: