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10 months ago
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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
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
- Mexican fleabane - a perennial plant with narrow, hairy leaves and daisy-type flower-heads.
- Cypress spurge - a 'vigorously spreading' perennial with very narrow blue-green leaves, and greenish-yellow flowers in late spring and early summer.
- Chameleon plant - a wide-spreading herbaceous perennial with leaves splashed and margined cream, often heavily red-flushed and dense flower spikes in late spring.
- 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.
- Purple top - a tall herbaceous perennial with oblong leaves and numerous branched clusters of small, lilac-purple flowers.
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
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:
- Mexican fleabane (Erigeron karvinskianus) - a perennial plant with narrow, hairy leaves and daisy-type flower-heads.
- Cypress spurge (Euphorbia cyparissias) - a 'vigorously spreading' perennial with very narrow blue-green leaves, and greenish-yellow flowers in late spring and early summer.
- 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.
- 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.
- 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)
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
