New Zealand pigmyweed

Crassula helmsii

Overview

Photo credit: ©Clare Dean

Crassula helmsii - New Zealand pigmyweed, Australian swamp stonecrop

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.

Download N.I.E.A. ID guide

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 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:

RAPID (Reducing and Preventing IAS Dispersal) LIFE - Good Practice Management - New Zealand Pigmyweed (Crassula helmsii)

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.

Current Legislative Position (Listed on 07 August 2025) This species must not intentionally be brought into the Union; kept; bred; transported to, from or within the United Kingdom, unless for the transportation to facilities in the context of eradication; placed on the market; used or exchanged; permitted to reproduce, grown or cultivated; or released into the environment.