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Plantlife calls for action on next generation of plant invaders

February 28 2011

Pirri-pirri-bur © Crown Copyright 2009. GBNNSS.

Pirri-pirri-bur © Crown Copyright 2009. GBNNSS.

Conservation charity Plantlife reveals the non-native plants most likely to be the next damaging invaders in our countryside in a new report launched today.

Most are on sale in garden and aquatics centres and are used in our gardens, ponds, aquaria and public spaces. Plantlife is calling for urgent action to be taken on plants assessed as having invasive potential should they escape ‘over the garden wall’, by conducting more detailed research to determine the level of threat they pose. For plants where the level of invasive threat is already evident, Plantlife is calling for better use of legislation to try and contain them.

The next invaders – the ‘ones to watch’

Plantlife’s new report ‘Here today, here tomorrow? Horizon scanning for invasive non-native plants’ (click here to download a copy) contains details of species that Plantlife believes are on the brink of becoming invasive in Britain but are not yet covered by legislation that could help to limit their spread. Invasive species already cause enormous problems to our native plants and wildlife, and cost the British economy around £1.7 billion every year.

Examples of invasive species not yet listed on appropriate legislation

Pirri-pirri-bur Acaena novae-zelandiae – garden plant originating from Australasia, now spreading into the wild and becoming invasive especially on sandy soils, cliffs, heaths & roadsides where it affects threatened native plants. Spreads through fly-tipping of garden waste, and subsequent transport by animals into the countryside.

Tree of heaven Ailanthus altissima – deciduous tree from China widely planted in gardens & public spaces, spread through seed dispersal, dumping & suckering. Prevents other plants from growing by releasing toxic compounds; cutting can result in more vigorous growth. Also known as the ‘tree of hell’ due to its invasiveness.

Large-flowered waterweed Egeria densa – submerged aquatic plant popular with aquarium owners, but plants are often discarded and dumped when they outgrow their tanks. May outcompete native aquatics, clog up waterways and drainage systems in future, especially as our climate changes.

Evergreen oak (holm oak) Quercus ilex – an evergreen tree used in parks and gardens, now widely established in parts of S and E England, on coasts and grassland, where it shades out rare native plants. It is already affecting some of our iconic landscapes including the Avon Gorge in Bristol and Great Orme in North Wales.

Turkey oak Quercus cerris – deciduous tree planted in woodlands, parks and along roads, now naturalised and spreading into grassland and heathland, and recorded from important wildlife sites. May become a major nuisance as it colonises open grassland and heathland and outcompetes more delicate native flora.

False-acacia Robinia pseudoacacia – suckering tree extensively planted in UK, and although currently uncommon in the countryside, is showing alarming signs of spreading along railway lines. It is spiny and impenetrable when established, and can easily regrow from stumps.

Legislation on invasive species

"In the long term, preventing potential problem plants from escaping into the wild in the first place is better – and cheaper – than waiting until these plants have already established themselves and need expensive control measures."

Victoria Chester, Plantlife Chief Executive

The most cost effective and least environmentally-damaging approach to solving the problems caused by invasive plants is to prevent them from escaping into the wild in the first place. Where plants are not yet widely established, this is best achieved by a ban on sale in Britain. In addition to plants consulted upon by Defra in 2008, Plantlife is calling for a ban on sale for Pirri-pirri-bur and Large-flowered waterweed.

Plantlife is calling for all the above six species to be listed on Schedule 9 of the Wildlife and Countryside Act 1981, which would make it an offence to plant these species in the wild or cause them to grow there.

“These species are on the brink of becoming invasive" said Plantlife Chief Executive Victoria Chester "but have been overlooked in recent legislative changes that aimed to provide better protection for the environment from such plants. In the long term, preventing potential problem plants from escaping into the wild in the first place is better – and cheaper – than waiting until these plants have already established themselves and need expensive control measures,”

“Plantlife is calling for urgent action before it’s too late.”

Rapid risk assessment process

The six species listed above are amongst 92 given a ‘critical’ ranking in a new rapid risk assessment screening process developed by Plantlife, which is designed to assign a broad level of invasive threat to non-native plant species. Plantlife recommends that comprehensive risk assessments should be carried out on these 92 species without delay – as for the vast majority this is not yet taking place.

Other species given a critical ranking include Japanese honeysuckle Lonicera japonica, Lawn marsh-pennywort Hydrocotyle sibthorpioides and New Zealand water-milfoil Myriophyllum elatinoides – these species need urgent further research and assessment to better determine the invasive threat they pose. Given the rapid nature of the screening process, plants identified as potentially invasive do not warrant trade or planting restrictions based on the rapid assessment alone, but the more detailed assessments can help determine whether they too warrant trade or planning restrictions.

For more information and images, please contact:

Justina Simpson Plantlife publicity manager T 01722 342730

or Email:

For information on invasives Email: