Photo: Australian Swamp Stonecrop - credit GBNNSS
Australian Swamp Stonecrop (Crassula helmsii) is also known as New Zealand Pigmyweed. It was widely sold by garden centres and aquatic centres for its excellent oxygenating properties. However once it had escaped into the environment it has proven to be a problematic non-native invasive species and since April 2014 has been banned from sale.
Crassula helmsii is suited to a wide range of slow moving freshwater systems and forms dense mats of vegetation year-round. It out-competes our native plants by depleting the oxygen levels in water, killing submerged plants such as algae and waterweeds and suppressing the germination of other native species. The resulting deoxygenated water has an adverse effect on invertibrates such as great crested newts, and fish.
Crassula helmsii is not harmful to humans but dense mats can be mistaken as dry land and therefore presents a potential hazard to people, dogs and livestock when present on public access sites.
The dense mats of vegetation can reduce the flow of water along waterways, increasing the risk of flooding and can impact the tourism and recreation of a waterway by preventing the passage of boats and making it impossible for anglers to fish.
Australian swamp stonecrop should be reported via the Recording Native Species Counts scheme.
You should record the presence of invasive species on a national database. This is easily done via the PlantTracker app. Alternatively you can record online at the Non-native Species Secretariat website. You should also alert the appropriate land owner, council and or management body to the presence and location of this plant.