Photo: Close-up of Australian Swamp Stonecrop (credit- GBNNSS)
Crassula helmsii is an aquatic, succulent perennial which grows throughout the year, forming dense, creeping mats of vegetation. It is tolerant of shade and extreme cold.
It's stems have pairs of fleshy unstalked opposite leaves (4-24 mm in length) borne alternately on rigid stems. The leaf bases are joined giving a distinctive 1mm collar.
The leaf shape is simple and varies from a long narrow near-parallel form, to very slightly elliptical with sharp or bluntish tip. This leaf tip distinguishes the underwater form of the plant from most native Starworts which have obviously notched leaf tips.
The flowers have short stalks and arise singly at the base of the leaves, they are four petalled, white or occasionally pale pink, with filaments and black anthers and appear between July-September.
Natural dispersal occurs by the transportation of vegetative fragments and the production of special short shoots called turions which break off and disperse by water currents. Fragments can also be transported by birds, other wildlife and livestock and can be unintentionally transported by humans on boots, angling nets, boats, heavy plant, vehicles and other recreational equipment.
You should record the presence of invasive species on a national database. 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.