Japanese knotweed is an invasive plant that can cause serious damage and legal issues if found on your property. But identifying it correctly can be tricky, as many other plants share similar traits. Here are the most common lookalikes mistaken for Japanese knotweed and how to tell them apart.
What Plants are Commonly Confused with Japanese Knotweed?
Several non-invasive plants are frequently mistaken for Japanese knotweed due to certain visual similarities. Here are the top offenders:
- Bindweed
- Russian Vine
- Houttuynia
- Himalayan Honeysuckle
- Ivy
- Broadleaf Dock
- Ground Elder
While they may look alike at first glance, a closer inspection reveals key differences that set them apart from knotweed.
Distinguishing Bindweed from Japanese Knotweed
Bindweed is a climbing vine that wraps around other plants and structures. Its heart-shaped leaves can resemble young knotweed, leading to identification errors.
However bindweed lacks the tall hollow, jointed stems of knotweed. Its thin vines use structures like fences or shrubs for support rather than standing upright on their own.
The twining habit and smaller heart-shaped leaves set bindweed apart from knotweed’s spade-shaped foliage and robust canes.
How to Tell Russian Vine and Japanese Knotweed Apart
Russian vine is closely related to Japanese knotweed and can form invasive thickets Its pointed, shovel-shaped leaves look similar to knotweed from a distance
But Russian vine is a scrambling vine rather than having rigid stems. It uses other plants or structures like fences for support, unlike self-supporting knotweed canes.
Russian vine also has larger greenish-white flowers and lacks the red speckles on joints that identify knotweed stems
Noticing the Differences Between Houttuynia and Knotweed
This low-growing garden perennial has heart-shaped leaves that cause it to be mistaken for young knotweed shoots.
However, houttuynia only reaches about 30 cm tall, unlike knotweed’s 2-3 meter height. It spreads via rhizomes but is not considered invasive.
The tiny white flowers of houttuynia are another distinguishing feature missing from knotweed plants.
Separating Himalayan Honeysuckle from Japanese Knotweed
Himalayan honeysuckle can appear similar to knotweed when young, with lush green leaves and red stems. But its foliage grows in pairs along stems rather than alternating.
Mature honeysuckle is a woody shrub reaching 6 feet, not a towering cane. And its hanging red berries are very distinctive.
Overall, it lacks knotweed’s aggressive spreading via rhizomes and is not invasive.
Recognizing Ivy’s Differences from Japanese Knotweed
The shiny lobed leaves of young ivy plants can be mistaken for knotweed if not compared closely. But ivy is a vining plant that climbs up structures and has aerial rootlets for clinging.
Ivy also keeps its leaves year-round rather than dying back in winter. And the juvenile three-lobed leaves morph into unlobed, oval mature foliage.
The woody stems and lack of hollow joints confirm that ivy is completely different from knotweed’s smooth, hollow canes.
Noticing Key Traits Separating Broadleaf Dock
Broadleaf dock leaves unfurl in spring looking somewhat similar to young knotweed foliage. However, they form circular basal rosettes around a central taproot rather than alternating along vining stems.
The taller flowering spikes of broadleaf dock also differ from knotweed’s shorter panicles. And dock lacks invasive rhizomes, spreading only by seeds.
Overall plant size is much smaller than knotweed, typically less than 3 feet tall. The fluted stems and stout taproot are also distinguishing dock features.
How Ground Elder Differs from Japanese Knotweed
Prolific ground elder forms dense patches that may be mistaken for stands of Japanese knotweed. However, its compound leaves made up of three leaflets are very different from knotweed’s simple ovate leaves.
The small white flowers on umbrella-like stems are also unique to ground elder. And while it spreads aggressively via rhizomes, it only reaches about 1 foot tall – much smaller than towering knotweed.
When in Doubt, Seek Expert Help
If you spot a plant that looks like it could potentially be Japanese knotweed, don’t panic. There are many lookalike plants, both native and ornamental.
To confirm identification, contact an invasive plant specialist for an expert assessment. Property owners can utilize free weed identification services through many knotweed control companies.
Proper identification is crucial before undertaking any control or removal measures. Misidentifying knotweed could lead to unnecessary treatment of non-invasive plants.
But rest assured, the majority of suspected knotweed cases turn out to be harmless lookalikes. Only a professional can conclusively diagnose Japanese knotweed on your property, bringing you peace of mind.
Himalayan Balsam (Impatiens glandulifera)
Dense Himalayan balsam growth
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. Similarities.
- The tallest annual plant in the UK is Himalayan balsam, which can grow up to 2 5m; thus reaching the same height as some mature knotweed.
- Stems are hollow.
- Many plants spread quickly and can take over large areas, especially near waterways.
Differences
- Leaves are arranged opposite each other along stems.
- The midribs of the leaves are pale pink and longer than those of knotweed. This can make them look a bit like Himalayan knotweed (Persicaria wallichii).
- The big, pink flowers with hoods and lips appear in the middle to end of summer.
- Soon after the flowers, the plant makes seed pods, which, when fully grown, explode when touched. This is how the plant sends seeds over several meters.
Horsetail (Equisetum arvense) Similarities
- The spore-bearing bodies, or strobili, show up in the spring and grow through the ground at a sometimes scary rate, making them look like they are spreading. People may worry that they are young Japanese knotweed shoots because of this.
- Once the strobili have released their spores, they die back. Soon after, the green stems and leaves appear in a similar way. These are broken up into nodes, which looks a bit like Japanese knotweed, so they might be mistaken for young knotweed shoots.
Differences
- Once the strobili die back, they are quickly replaced by green shoots and leaves that grow quickly into the brush-like growth that gives horsetail its name. These are very different from mature Japanese knotweed plants and don’t look at all like them.
Plants That Look Like Japanese Knotweed: Plants Commonly Mistaken For Japanese Knotweed
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