Introduced to Britain in the 1980s through the aquatic trade Hydrocotyle ranunculoides, commonly known as floating pennywort, is rapidly spreading through Europe and particularly in the UK, Belgium, Germany, Italy, France and the Netherlands. Originating in Central and South America, this stoloniferous perennial plant is forming dense, impenetrable mats which rapidly dominate water bodies, outcompeting and displacing native species and compromising flood defences, navigation and leisure activities. Despite its relatively recent introduction, establishment and spread have been exponential thanks largely to its extremely fast growth rate (up to 20cm per day) and its ability to re-generate from small fragments. In 2010, floating pennywort was added to section 14, schedule 9 of the UK’s Wildlife and Countryside Act 1981. A recent report estimates its cost to Great Britain’s economy as £25.5 million each year through management, disposal, flooding and indirect costs to boating and angling. News that from 2014 the sale of this plant will be banned is significant and welcomed.