It has been growing uncontrollably across Britain since being introduced nearly 200 years ago. 

But Japanese knotweed isn’t the only invasive plant that gardeners will have to contend with in the near future. 

That’s according to a new study, which has revealed the plants with the greatest potential to wreak havoc on British gardens. 

Based on reports from 558 gardeners, researchers from the University of Reading have identified over 200 potential invaders – including five of particular interest. 

So, do you have any lurking in your backyard? Scroll to the bottom for the full list. 

A new study has revealed the plants with the greatest potential to wreak havoc on British gardens. Pictured: Mexican fleabane

A new study has revealed the plants with the greatest potential to wreak havoc on British gardens. Pictured: Mexican fleabane

Based on reports from 558 gardeners, researchers from the University of Reading have identified over 200 potential invaders, including Cypress spurge

Based on reports from 558 gardeners, researchers from the University of Reading have identified over 200 potential invaders, including Cypress spurge 

The 5 potentially invasive plants you might already have in your garden 

  1. Mexican fleabane – a perennial plant with narrow, hairy leaves and daisy-type flower-heads. 
  2. Cypress spurge – a ‘vigorously spreading’ perennial with very narrow blue-green leaves, and greenish-yellow flowers in late spring and early summer. 
  3. Chameleon plant – a wide-spreading herbaceous perennial with leaves splashed and margined cream, often heavily red-flushed and dense flower spikes in late spring. 
  4. Himalayan honeysuckle – a vigorous, deciduous shrub with erect sea-green stems bearing long-pointed, ovate leaves and white flowers with showy red-purple bracts, followed by deep purple berries. 
  5. Purple top – a tall herbaceous perennial with oblong leaves and numerous branched clusters of small, lilac-purple flowers. 

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Japanese Knotweed is a species of plant that has bamboo-like stems and small white flowers.

Native to Japan, the plant is considered an invasive species, and was brought to Britain by the Victorians as an ornamental garden plant and to line railway tracks to stabilise the soil.

Despite looking pretty, Japanese knotweed can seriously damage buildings and construction sites if left unchecked.

In their new study, the researchers set out to discover similar plants that show ‘invasive behaviour’ in British gardens. 

‘The majority of our ornamental plants are non-native,’ the team explained. 

‘They contribute greatly to our enjoyment of gardens and represent a long history of plant discovery and garden design.

‘However, some have escaped the controlled environment of gardens, and a small minority of these are threatening native biodiversity or are causing severe problems for infrastructure, agriculture or forestry. 

‘Well known examples include Japanese Knotweed (Reynoutria japonica), Rhododendron ponticum and Himalayan Balsam (Impatiens glandulifera).’

The team created an online survey and received reports from 558 gardeners, revealing more than 200 potential invaders. 

An analysis of the results, considering both domestic and global invasive status, allowed the researchers to prioritise five ornamental plants of concern. 

‘The simple yet structured scheme we developed was used to prioritise which of the around 70,000 ornamental plants available to buy in the UK could be future invaders,’ said lead author, Tomos Jones. 

The team created an online survey and received reports from 558 gardeners, revealing more than 200 potential invaders. Pictured: purple top

The team created an online survey and received reports from 558 gardeners, revealing more than 200 potential invaders. Pictured: purple top 

An analysis of the results, considering both domestic and global invasive status, allowed the researchers to prioritise the ornamental plants of concern. Pictured: Himalayan honeysuckle

An analysis of the results, considering both domestic and global invasive status, allowed the researchers to prioritise the ornamental plants of concern. Pictured: Himalayan honeysuckle

‘This is crucial for focusing research efforts and resources, such as conducting formal risk assessments to explore the invasive potential of those shortlisted.’ 

The researchers highlight five shortlisted plants, which many Britons may already have in their gardens:

  1. Mexican fleabane (Erigeron karvinskianus) – a perennial plant with narrow, hairy leaves and daisy-type flower-heads. 
  2. Cypress spurge (Euphorbia cyparissias) – a ‘vigorously spreading’ perennial with very narrow blue-green leaves, and greenish-yellow flowers in late spring and early summer. 
  3. Chameleon plant (Houttuynia cordata) – a wide-spreading herbaceous perennial with leaves splashed and margined cream, often heavily red-flushed and dense flower spikes in late spring. 
  4. Himalayan honeysuckle (Leycesteria formosa) – a vigorous, deciduous shrub with erect sea-green stems bearing long-pointed, ovate leaves and white flowers with showy red-purple bracts, followed by deep purple berries. 
  5. Purple top (Verbena bonariensis) – a tall herbaceous perennial with oblong leaves and numerous branched clusters of small, lilac-purple flowers. 
The researchers highlight five shortlisted plants, which many gardeners may already have in their gardens, including Chameleon plant (pictured)

The researchers highlight five shortlisted plants, which many gardeners may already have in their gardens, including Chameleon plant (pictured) 

John David, RHS Head of Horticultural Taxonomy, added: ‘It’s important to remember that these shortlisted plants are not yet officially invasive.

‘Many non-native plants that occur in the wild present no threat to our native biodiversity.’

Based on the findings, the researchers are calling for authorities to assess the potential for these plants to become invasive in Britain and Ireland, before it’s too late. 

‘The period between introduction of a species and it first being noticed as a problem can be a long one, making future control problematic,’ the team added. 

‘In Britain on average, this time span has been more than one hundred years. 

‘Early detection of potentially problematic plants for further risk assessment could greatly improve our ability to prevent plant species becoming invasive.’

The full list of potentially invasive species in British gardens 

Acanthus mollis

Acanthus spinosus

Acer platanoides

Acer pseudoplatanus

Adenophora khasiana

Aegopodium podagraria

Agastache rugosa

Ailanthus altissima

Akebia quinata

Alchemilla mollis

Alkekengi officinarum

Allium hollandicum

Allium roseum

Allium triquetrum

Amaranthus cruentus

Anemanthele lessoniana

Anemone x hybrida

Angelica archangelica

Arisaema ciliatum

Arisarum proboscideum

Arum italicum

Arum italicum subsp italicum

Astrantia major

Borago officinalis

Briza maxima

Brunnera macrophylla

Buddleja davidii

Calendula officinalis

Camassia leichtlinii subsp leichtlinii

Campanula carpatica

Campanula lactiflora

Campanula medium

Campanula portenschlagiana

Campanula rapunculoides

Carex buchananii

Carex comans

Catananche caerulea

Centranthus ruber

Cephalaria gigantea

Cerastium tomentosum

Ceratostigma willmottianum

Cerinthe major

Chaenomeles speciosa

Chimonobambusa tumidissinoda

Clematis montana

Clematis tangutica

Clerodendrum bungei

Clerodendrum trichotomum

Cornus alba

Cornus controversa

Cornus mas

Cotoneaster horizontalis

Crocosmia x crocosmiiflora

Crocosmia fucata x paniculata

Crocus tommasinianus

Cyanus montanus

Cyclamen coum

Cyclamen hederifolium

Darmera peltata

Dicentra formosa

Duchesnea indica

Echinops ritro

Echium pininana

Equisetum scirpoides

Eragrostis elliottii

Erigeron annuus

Erigeron karvinskianus

Eschscholzia californica

Euphorbia x martini

Euphorbia amygdaloides subsp robbiae

Euphorbia cyparissias

Euphorbia helioscopia

Euphorbia mellifera

Eurybia divaricata

Eutrema japonicum

Fallopia baldschuanica

Fargesia murielae

Fragaria x ananassa

Geranium x oxonianum

Geranium endressii

Geranium macrorrhizum

Geranium nodosum

Geranium palustre

Geranium phaeum

Geranium pyrenaicum

Gladiolus communis

Gunnera magellanica

Gunnera tinctoria

Hedera algeriensis

Helianthus x laetiflorus

Helianthus tuberosus

Helleborus orientalis

Hemerocallis fulva

Hesperantha coccinea

Hesperis matronalis

Houttuynia cordata

Hyacinthoides x massartiana

Hyacinthoides hispanica

Hypericum x hidcoteense

Hypericum x inodorum

Hypericum calycinum

Impatiens glandulifera

Inula hookeri

Jasminum nudiflorum

Jasminum officinale

Kerria japonica

Lagarosiphon major

Lamium galeobdolon subsp argentatum

Lamium maculatum

Lathyrus latifolius

Lathyrus neurolobus

Lathyrus odoratus

Lathyrus vernus

Laurus nobilis

Leptinella squalida

Leycesteria formosa

Libertia chilensis

Limnanthes douglasii

Linaria purpurea

Lobelia pedunculata

Lonicera x purpusii

Lonicera japonica

Lonicera ligustrina var yunnanensis

Lycium barbarum

Lysimachia ciliata

Lysimachia clethroides

Lysimachia punctata

Melissa officinalis

Mimulus guttatus

Mimulus luteus

Muehlenbeckia complexa

Muscari armeniacum

Myosotis arvensis

Myriophyllum aquaticum

Nassella tenuissima

Nicandra physalodes

Nigella damascena

Nigella sativa

Oberna multifida

Oenothera fruticosa

Omphalodes cappadocica

Onoclea sensibilis

Ornithogalum arabicum

Oxalis corniculata

Oxalis magellanica

Paeonia ludlowii

Papaver nudicaule

Pappobolus microphyllus

Parthenocissus quinquefolia

Patrinia scabiosifolia

Pentaglottis sempervirens

Persicaria amplexicaulis

Persicaria campanulata

Persicaria virginiana var filiformis

Petasites fragrans

Petasites japonicus

Phalaris arundinacea var picta

Phalaris arundinacea

Phlomis russeliana

Phygelius capensis

Phyllostachys aurea

Phyllostachys nigra

Physostegia virginiana

Phytolacca acinosa

Phytolacca americana

Picea sitchensis

Pilosella aurantiaca

Pleioblastus viridistriatus

Polygonum microcephalum

Polygonum runcinatum

Primula prolifera

Prunus laurocerasus

Prunus lusitanica

Pseudofumaria lutea

Quercus ilex

Reynoutria japonica

Rhododendron ponticum

Rhus typhina

Ribes sanguineum

Robinia pseudoacacia

Rodgersia podophylla

Rosa gallica

Rosa rugosa

Rubus rolfei

Rubus spectabilis

Rubus thibetanus

Rubus tricolor

Saponaria officinalis

Sauromatum venosum

Saxifraga x urbium

Scilla luciliae

Sedum rupestre

Sedum spectabile

Sedum spurium

Semiarundinaria fastuosa

Silphium perfoliatum

Silybum marianum

Soleirolia soleirolii

Spiraea x billardii

Stachys byzantina

Stachys macrantha

Strobilanthes wallichii

Symphoricarpos albus

Symphyotrichum x salignum

Symphyotrichum novi-belgii

Symphytum caucasicum

Symphytum grandiflorum

Symphytum ibericum

Syringa vulgaris

Tanacetum parthenium

Tellima grandiflora

Tetrapanax papyrifer

Teucrium hircanicum

Thamnocalamus spathiflorus

Trachystemon orientalis

Tropaeolum ciliatum

Verbena bonariensis

Verbena hastata

Verbena incompta

Vinca difformis

Vinca major

Vinca major var oxyloba

Vinca minor

Viola labradorica

 

This post first appeared on Dailymail.co.uk

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