New Zealand Pigmyweed (also known as Australian Swamp Stonecrop) was originally introduced to Britain in the early twentieth century as an oxygenating plant for ponds. In recent years, it has spread rapidly into the wild, where it forms dense mats in ponds and displaces native water plants. It is now an offence to introduce this plant into the wild.
The 4-petalled flowers are small and whitish-green or slightly pink. The leaves are fleshy when the plant emerges from water, and more flattened when underwater.