New Zealand pigmyweed

Crassula helmsii


Habitat: Generally grows on the margins of freshwater systems and can tolerate waters up to 3m in depth. It is present all year round.

Description: 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.


Origin and Distribution: Native to New Zealand and Australia.


Impacts: 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 vegetations 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.


Where is it found in Ireland? Crassula helmsii is known in the wild from a number of sites both the North and South of Ireland. The number of garden ponds with this species is not known.


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
Invasive Species Ireland

Invasive Species Ireland