Lagarosiphon, Oxygen Weed

South Africa

General description

Bottom-rooted submerged perennial aquatic herb. Stems are < 2 m long and branching. Leaves are < 16 x 2 mm, curved downwards and arranged spirally around stem. Flowers are minute and pink.

What you need to know

To help protect our environment:

  • You must not breed, distribute, release or sell lagarosiphon. As lagarosiphon is a National Pest Plant Accord species, these restrictions apply within the Auckland region and across the whole of New Zealand.
  • You must not plant lagarosiphon within the Auckland region.
  • You must destroy any lagarosiphon on land that you occupy if it has been planted in breach of the above rules and you are directed to do so by an authorised person.
If you see lagarosiphon anywhere on Aotea/Great Barrier Island group, please report it to Auckland Council at

Static to moderately fast-flowing freshwater bodies < 6.5 m deep.

Vegetative spread from stem fragments, dispersed by water movement. Human-mediated dispersal through contamination of boats, fishing gear and machinery and deliberate plantings.

Forms dense stands, displacing native aquatic herb species, altering habitat availability for fish and invertebrates, and affecting dissolved oxygen levels. Can impede recreational water access to water bodies.

Site Management

Very difficult to control once established. Consider an aquatic pest plant control operator. Contact Auckland Council for control options. Spraying aquatic weeds result in plants rotting in the water. This decreases dissolved oxygen in the water and in large amounts can kill aquatic life. Consider pulling out and only spraying regrowth in spring.

Recommended approaches

Do not attempt to undertake control of this species on Aotea/Great Barrier Island group. Please report to Auckland Council if seen on Aotea/Great Barrier Island group.

Physical control

Method: Pull out

Plant parts requiring disposal: All parts

Disposal options: Remove to greenwaste or landfill if practical


Biocontrol is currently not available for this species.

CAUTION: When using any herbicide or pesticide please read the label thoroughly to ensure that all instructions and safety requirements are followed.

Similar species

Egeria densa

Egeria has its leaves arranged oppositely in whorls on the stem.

Hydrilla verticillata

Hydrilla has less leaves on a stalk and toothed leaf margins.

southern naiad
Najas guadalupensis

S naiad has toothed leaf margins and it's leaves are on short branches.

Search tags

RPMP status

Aotea (Exclusion)
National Pest Plant Accord Species
Whole region (Sustained Control)
Lagarosiphon, oxygen weed - Main species image