The new knotweed: Warning over more alien plants set to wreak havoc

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Their exotic colours and leaves brighten up homes, gardens, ponds and parks across the land. But a host of popular plants are threatening to take over the countryside, according to experts.A report today names 92 non-native plants sold by garden centres and pond specialists that are in danger of spreading into the wild.

The charity Plantlife says many of the species could become the next Japanese knotweeds alien plants choking the countryside after being set loose by careless gardeners.Plantlife is calling for urgent action to curb the spread of the invaders and for two plants to be banned from sale.

Japanese knotweed: Report names 92 non-native plants which could spread into the wildInvasive plants and animals are thought to cost the economy around 1.7billion every year in damage to buildings, roads, woodlands and farms.The new list features species that are on the brink of becoming invasive but which are not covered by laws that would limit their spread.These include the large-flowered waterweed, a green leafy plant popular with owners of fish tanks that Plantlife wants banned.The plants are often thrown out when they get too big for their tanks. Once in the wild, they can clog up waterways and drainage systems in warm weather.The charity also wants garden centres to stop selling pirri-pirri bur, a fast-growing shrub from New Zealand that can smother native wildflowers. The plant spreads through fly-tipping of garden waste and is seen on sandy soils, road verges, heaths and cliffs where its seeds are spread by animals. Like many invasive plants, there are few natural checks on its growth.The charity also wants to make it an offence to plant other species ranked as critical in the wild.These include tree of heaven, a deciduous tree from China foun! d in gar dens and parks that poisons rivals, the evergreen oak from the Mediterranean, the Turkey oak from the near east and the false acacia from America. Plantlifes chief executive, Victoria Chester, said: These species have been overlooked in recent legislative changes that aimed to provide better protection for the environment from invasive species.

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In the long term, preventing potential problem plants from escaping into the wild in the first place is better and cheaper than waiting until they have established themselves and need expensive control measures. Other species given a critical ranking include Japanese honeysuckle, lawn marsh pennywort and New Zealand water milfoil.The charity says the problem species are just a small fraction of the 70,000 non-native plants available to buy in the UK.The most pernicious alien plant in Britain is the Japanese knotweed, which was introduced in 1840 and now costs around 179million a year to clear. It grows to around 9ft in only four months and can rip through concrete.