New Zealand pigmyweed

Crassula helmsii


Photo credit: ©Clare Dean
Crassula helmsii
  • Generally grows on the margins of freshwater systems and can tolerate waters up to 3m in depth. It is present all year round.

  • The shoots are rather stiff, carrying narrow parallel-sided leaves in opposite pairs, each leaf being about 4 - 24mm. Small white flowers with four petals are produced in summer on long stalks arising from the upper leaf axils. The flowers are always above water.

Download N.I.E.A. ID guide

Origin and Distribution:
  • Native to New Zealand and Australia.

  • This species is suited to a wide range of environmental tolerances and is well adapted to Irish conditions. Most slow moving freshwater systems are believed to be susceptible to invasion by C. helmsii. It forms dense carpets of monospecific vegetation and out competes native species choking ponds and ditches.

How did it get here?
  • It is believed that this plant got to Ireland via trade for garden ponds. It is possible that the species was disposed of or escaped into the wild from private gardens.
  • Secondary spread by animals and human activity from an infested site to new sites may occur.

Is it found in Northern Ireland?
  • It is found in the wild in Northern Ireland. The number of garden ponds with this species is not known. More distribution information can be found at NBN Atlas NI.

You can help by reporting any sightings: @ the Centre for Environmental Data & Recording (CEDaR) - Or via the iRecord App.
Further Resources:
Prevent Spread:
  • Promote native species and biodiversity - use alternative, native plants
  • Know what you are buying/growing and source native Irish seed and plants
  • Do not swap plants and cuttings
  • Clean plants before adding to ponds (dispose of water away from water courses)
  • Follow control advice and watch out for hitchhikers - inspect new imported purchases for invasive pest and pathogens
  • Clean equipment before moving between waterbodies
  • Never collect plants from the wild
  • Safe disposal of plant material and growing media
  • Report all sightings.

New Zealand pigmyweed research:

Effectiveness of eradication measures for the invasive Australian swamp stonecrop Crassula helmsii

For further queries, you can contact the Invasive Non Native Species (INNS) Team in the Northern Ireland Environment Agency on 028 9056 9558 or Email:

Species Related Files:

Invasive Species Ireland

Invasive Species Ireland