Plants That Look Like Japanese Knotweed
What Plants are Similar to Japanese Knotweed?
We receive hundreds of photographs from people keen to know if they might have Japanese knotweed on their properties. The following list has been compiled from the most common plants sent to us to identify. This is our list of ‘usual suspects’, so please take a look at the photographs and descriptions below before you send us your own pictures, as your concerns could quickly be allayed. The vast majority of photos sent to us are one of these species and not knotweed at all. (click on image to enlarge)
Woody Shrubs and Trees
- The leaf shape of many woody shrubs and small/young trees can look very similar to knotweed (e.g. lilac, dogwood and poplar).
- Knotweed stems are not at all woody, so anything with bark that can be stripped or twigs that snap to show a solid, woody core are not knotweed.
- Dogwood and lilac are often confused with knotweed due to their similar leaf shapes. However, these species have leaves that grow opposite each other along their woody stems.
Houttuynia (Houttuynia cordata)
- Shoots and leaves are very similar to young knotweed shoots. So much so that around 1825, when Japanese knotweed was first introduced to the UK by the Horticultural Society of London at their Chiswick garden, the plant was erroneously thought to be Houttuynia cordata.
- Plants only grow to 30cm or so in height.
- Flowers are produced in spring and appear to have four to six, large, white, petals (they are actually flower bracts at the base of the yellowish flower spikes).
Ornamental Bistorts (e.g. Red Bistort – Persicaria amplexicaulis)
- Ornamental bistorts are commonly planted decorative garden species. They are closely related to Japanese knotweed and are in the same genus as Himalayan knotweed (Persicaria wallichii).
- Red bistort is probably the most common. It and many other ornamental bistorts have leaves and stems that are very similar to knotweed species, and when not in flower they can easily be mistaken for them.
- Stems are hollow and separated into nodes like knotweed.
- Leaves are alternately arranged along stems, like knotweed.
- Ornamental bistorts are usually planted on purpose and don’t spread widely. Therefore they are usually located in planted borders and areas of landscaping.
- Flowers appear in summer and early autumn and are very different to those of Japanese knotweed. They form small clusters of pale pink/white to bright red/purple ‘lollipops’ on tall (10cm) straight ‘sticks’.
- Leaves are longer than those of Japanese knotweed, appearing more like those of Himalayan knotweed, with marked lobes that overlap slightly around the stems.
- Bistorts have very long, semi-translucent, leaf sheaths that envelop the stem nodes (bamboo-like rings from where leaves sprout) for almost the entire length of the stem internodes (the smooth, straight bits of stem between the nodes). These sheaths are absent on Japanese knotweed and are generally shorter on Himalayan knotweed.
- Stems are much thinner and shorter than knotweed, generally growing to around 1m tall and less than 1cm in diameter.
- Some varieties and species of ornamental bistort have dark, triangular, arrow-shaped blotches across the central midribs of the leaves.
Lesser knotweed (Persicaria campanulata)
- Lesser knotweed is another relatively common ornamental Persicaria species that is closely related to Himalayan knotweed (Persicaria wallichii). As such it is often mistaken for this species or for Japanese knotweed.
- As with other knotweed species, lesser knotweed has the same, bamboo-like, hollow stems with alternately arranged leaves.
- Leaves are long, thin and ovate (i.e. an elongated ellipse-shape) with clearly marked parallel veins, unlike Japanese knotweed.
- Lesser knotweed is shorter than Japanese knotweed, growing approximately 1.5m tall.
- Individual flowers are much bigger than those of Japanese knotweed and are clearly bell-shaped. They range in colour from pale to bright pink.
Himalayan Balsam (Impatiens glandulifera)
You can read all about this invasive non-native weed on our Himalayan balsam page. It contains details on: why it’s a problem; how to identify it; and how to control it. There are also links to other sources of useful guidance.
- Himalayan balsam is the tallest annual plant in the UK, growing up to 2.5m; thus reaching the same height as some mature knotweed.
- Stems are hollow.
- Plants are very invasive and can cover large areas – particularly close to watercourses.
- Leaves are arranged opposite each other along stems.
- Leaves are longer and thinner than those of knotweed and have a pale pink midrib (which can make them look a bit like Himalayan knotweed – Persicaria wallichii).
- Flowers form in mid to late summer and are large, pink, hooded and lipped.
- Seed pods follow shortly after flowers and once mature are explosive when touched (this is the plant’s mechanism for seed dispersal over several metres).
Broadleaved Dock (Rumex obtusifolius)
- Docks are in the same family as knotweed (Polygonaceae) so it’s not surprising they share several similar features.
- Leaves are arranged alternately along stems.
- Flowers and seeds form in spikes that look similar to knotweed.
- In winter, when the leaves and stems die back, the persistent stems of dock, with their old seed bracts, can look very similar to dead knotweed stems and seed bracts.
- Stems are fluted and are shorter than knotweed plants, growing up to 1m tall.
- Stems are not completely hollow, containing a foam-like pith.
- Leaves form rosettes close to the ground at the base of the stems and are much larger than those of knotweed (up to 1m long).
Bindweed (Convulvulus arvensis)
- Heart-shaped leaves can look similar to knotweed.
- Leaves are arranged alternately along stems.
- Plants are invasive and can very quickly appear in early spring, covering wide areas.
- Bindweed shoots do not stand up by themselves. It is a climbing plant that grows by twisting around the erect stems of other plants.
- Flowers appear from early summer as large, pink or white, trumpets.
- Stems have clear nodes like knotweed and can grow as tall, or taller.
- Plants can be invasive and easily spread to areas where they are not wanted. They can also be very difficult to effectively treat with herbicides.
- Growth of new shoots are from creeping rhizomes and can be extremely rapid (bamboos are the fastest growing plants in the world!).
- Stems are very hard and cannot be snapped easily like knotweed.
- Leaves are very slender and long (varies between species and varieties, but usually up to 50cm).
Himalayan Honeysuckle (Leycesteria formosa)
- Stems are bamboo-like and can look a lot like knotweed. They are also mostly hollow and can be snapped relatively easily.
- Leaves are arranged opposite each other along the stems.
- Stems are pale green with no purple speckles.
- Flowers appear in summer and autumn and are very distinct, forming drooping, pendulous racemes of white flowers, with showy red-purple bracts. Deep purple berries later form along the racemes, between the red-purple bracts.
Russian Vine (Fallopia baldschuanica)
- Russian vine is in the same genus (Fallopia) as knotweed. As such, pollen from Russian vine commonly pollinates the female flowers of Japanese knotweed. However, the resulting seed almost never produces viable plants.
- Being closely related, the leaves and flowers of Russian vine appear quite similar to those of knotweed.
- It is incredibly fast growing and invasive – its common name is ‘mile-a-minute’!
- Russian vine is a climbing plant that relies on the erect stems of other plants or solid structures to twist around and grow upon. As such, it is very commonly used as a screening plant or to quickly provide cover over fences and other structures.
If you still think that you might have Japanese knotweed then our expert consultants can identify it for you for free! If you do happen to have Japanese knotweed then we offer a Japanese knotweed removal service, so get in touch with us today to start your consultation.