Stout water milfoil Myriophyllym robustum

Key Features

  • A stout aquatic herb with fleshy branches to 1.6 m long, the tips of which emerge above the water surface. Leaves are produced in rings around the branches, and are very finely cut into small segments. The leaves are pointed in outline, distinguishing this species from the introduced parrot’s feather (Myriophyllum aquaticum) which has leaves that are rounded at the tip. The green or pink flowers are tiny and borne in the upper leaf axils.

Distribution and Habitat

  • North and South Islands, from Kaitaia to Fiordland, and confined to Nelson, Westland and Fiordland in the South Island. Stout water milfoil occurs in peaty ponds, slow moving streams and lagoon or lake margins where the water is between 0.5-2 m deep.


  • Habitat modification and loss.
  • Changes in hydrology.
  • Competition with invasive weeds such as willow.
  • Eutrophication due to nutrient runoff.
  • Animal browse (goats and possums).

Management Opportunities

  • Survey for new locations.
  • Mark known sites.
  • Protection of habitat.
  • Restoration of habitat and re-establish plants from cuttings.
  • Clear exotic weeds.
  • Possum and goat control.
  • Ensure that forest owners are aware of potential habitats and can recognise the species.

Monitoring Options

  • Check existing populations annually.
  • Report new locations to DOC, NZPCN.

Further Information and Support

  • New Zealand Plant Conservation Network (NZPCN).
  • References:
    • Dopson et al. (1999). The conservation requirements of New Zealand’s nationally threatened vascular plants. Threatened Species Occasional Publication 13. Department of Conservation, Wellington.
    • Johnson & Brooke (1989). Wetland plants in New Zealand. DSIR Publishing, Wellington.
    • Wilson & Given (1989). Threatened plants of New Zealand. DSIR Publishing, Wellington.