About Crassula helmsii (Kirk) Cockayne
Crassula helmsii (Kirk) Cockayne has rather stiff shoots that bear narrow, parallel-sided leaves arranged in opposite pairs. Each leaf measures approximately 4–24 millimetres (0.16–0.94 in) in length. In summer, small white flowers with four petals grow on long stalks that emerge from the upper leaf axils, and these flowers always sit above the water surface.
As of 2010, C. helmsii has been recorded throughout the British Isles, as well as in the Netherlands, Belgium, the United States, Russia, France, Germany, Italy and Spain. In Ireland, it has been recorded growing on waste ground at Howth Head, County Dublin, and at multiple sites in Northern Ireland.
In cultivation, C. helmsii can grow fully submerged in cool-water aquariums, or as a submersed or marginal plant in ponds. Once it becomes established, it grows very vigorously and may require regular trimming. Under Schedule 9 of the UK Wildlife and Countryside Act 1981, this species is listed as a plant that must not be allowed to grow in the wild.
