Information on New Zealand Pigmyweed

Common Name: New Zealand Pigmyweed
Scientific Name: Crassula helmsii
Irish Name: Crasal Nua-Shéalannach
Family Group: Crassulaceae
Distribution: View Map (Courtesy of the BSBI)
Flowering Period


Click for list of all flowering by month
New Zealand Pigmyweed is not easily confused with other wild plants on this web site.


This is a succulent, prostrate, perennial plant which has come to us from the Antipodes where it is known as Australian Swamp Stonecrop. It has very small, long-stalked, whitish-pink 4-petalled, star-like flowers (1-2mm across) which are solitary in the leaf axils. The petals are longer than the sepals which are visible between the petals. The fleshy leaves are narrow, pointed, in pairs which are joined around the pink stems with a dark ring at the base of each junction or node. It blooms from June to September and belongs to the Crassulaceae or Stonecrop family. It colonises ponds where it forms carpets in the muddy margins, across the roots of other plants and it does not die back in winter. 

I first came across this species while clearing out a pond in Co Wexford in September 2014 when I also photographed it. At first I was quite excited, as I always am when I find a new (to me) species. However, it was not as joyful a find as it first appeared to be. See left.....

If you are satisfied you have correctly identified this plant, please submit your sighting to the National Biodiversity Data Centre

Pigmyweed, New Zealand
Pigmyweed, New Zealand

New Zealand Pigmyweed is one of the plant species which is listed as a non-native species and is subject to certain restrictions under our Protection of Fauna and Flora Regulations 49 & 50. These restrictions basically say that, among other things, ‘a person shall be guilty of an offence if he or she has in his or her possession for sale, or for the purposes of breeding, reproduction or propagation, or offers or exposes for sale, transportation, distribution, introduction or release’ of an animal or plant on that particular list. 

First recorded in Ireland in 1984, this plant has been sold, in the past, for use in garden ponds and aquariums but has the potential to eliminate our native plants and cause all sorts of problems for the creatures living in this type of habitat. Its invasive potential has been graded as ‘High Impact’ by the National Biodiversity Data Centre who caution that this plant is also a ‘possible health hazard, as the thick mats can be mistaken for dry land’. They also warn that ‘the thick mats cause shading of existing water plants and the depletion of oxygen in the water which leads to a reduction of native flora and fauna’.