African oxygen weed

Lagarosiphon major syn. Elodea crispa, Lagarosiphon muscoides
Aquatic
Alternate
Simple
Pink
Green

Lagarosiphon (Lagarosiphon major) is 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. It is also regarded as an emerging environmental weed in Tasmania, and as a potential environmental weed  in many parts of Australia (including south-eastern Queensland).

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.).

Common names 
Also known as: African elodea, coarse oxygen weed, curly water thyme, lagarosiphon, oxygen plant, oxygen weed,, South African oxygen weed,
Family 
Hydrocharitaceae
Deciduous 
No
Flowering time 
Summer, early Autumn
Native/Exotic 
Exotic
Origin 
Native to central and southern Africa.
Notifiable 
No
State declaration 
Category 3 - Must not be distributed or disposed. This means it must not be released into the environment unless the distribution or disposal is authorised in a regulation or under a permit.
Council declaration 
As per State Declaration
Known distribution 

Not yet known to be naturalised in south-eastern Queensland.

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.

Habitat 

A potential weed of slow-moving waterways, ponds, lakes and dams, that is mainly a threat to 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).

Lagarosiphon (Lagarosiphon major) is 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. It is also regarded as an emerging environmental weed in Tasmania, and as a potential environmental weed  in many parts of Australia (including south-eastern Queensland).

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.).

Stem 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 fruits 

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.

Similar species 

Lagarosiphon (Lagarosiphon major) can be confused with other submerged water weeds such as dense waterweed (Egeria densa ), elodea (Elodea canadensis), and the native hydrilla (Hydrilla verticillata). These species can be differentiated by the following differences:

lagarosiphon (Lagarosiphon major) has elongated (i.e. strap-like) leaves that are bent backwards (i.e. strongly recurved) and have very finely toothed (i.e. serrulate) margins. These leaves are somewhat crowded along the stems, stalkless (i.e. sessile), and alternately arranged in a distinctive spiralling pattern. Its inconspicuous pink or purplish flowers are very small (only 3 mm across) with six tiny 'petals' (i.e. perianth segments) and are borne on the water surface on long stalks.

dense waterweed (Egeria densa ) has elongated (i.e. strap-like) leaves with very finely toothed (i.e. serrulate) margins. These leaves are densely crowded along the stems, stalkless (i.e. sessile), and usually arranged in groups (i.e. whorls) of four or five. Its flowers are relatively large with three broad white petals (9-12 mm long) and are borne on the water surface on relatively short 'stalks' (2.5-7.5 cm long).

elodea (Elodea canadensis) has oblong or elongated (i.e. strap-like) leaves with very finely toothed (i.e. serrulate) margins. These leaves are less crowded, stalkless (i.e. sessile), and usually arranged in groups (i.e. whorls) of three. Its white flowers are relatively small with three slender petals (up to 5 mm long) and are borne on the water surface on long 'stalks' (up to 30 cm long).

hydrilla (Hydrilla verticillata) has elongated (i.e. strap-like) leaves with very finely toothed (i.e. serrulate) margins. These leaves are less crowded, stalkless (i.e. sessile), and usually arranged in groups (i.e. whorls) of four to six. Its inconspicuous greenish flowers are very small (only 3 mm across) with six tiny 'petals' (i.e. perianth segments) and are borne on the water surface on long stalks.