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Equal-leaved Knotgrass

Polygonum arenastrum

Please keep in mind that it is illegal to uproot a plant without the landowner's consent and care should be taken at all times not to damage wild plants. Wild plants should never be picked for pleasure and some plants are protected by law.
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Plant Profile

Flowering Months:
Polygonaceae (Dock)
Life Cycle:
Annual, Biennial or Perennial
Maximum Size:
15 centimetres tall
Beaches, roadsides, rocky places, saltmarshes, sand dunes, seaside, wasteland.

Pink, 5 petals
Flowers are either solitary or in clusters of 2 and 3. They are pale green, pinkish or white. The flowers are slightly smaller than those of the similar looking Common Knotgrass (Polygonum aviculare). Equal-leaves Knotgrass also flowers about 1 month later. Insect pollinated.
Dark red or brown, 3-edged achene. The seeds ripen from August to October.
Oval, stalkless leaves. Unlike the similar looking Common Knotgrass (Polygonum aviculare), its stems are mat-forming and the leaves are stubbier. The stems can spread up to 1.2 metres. All of the leaves are the same size. It is also an annual plant with alternate, hairless leaves. Equal-leaved Knotgrass is almost as common as Common Knotgrass in the UK.
Other Names:
Beach Knotweed, Birdweed, Common Knotweed, Door Weed, Mat Grass, Oval-leaf Knotweed, Prostrate Knotweed, Silverweed, Small-Leaved Knotweed, Stone Grass, Wiregrass, Wireweed.
Frequency (UK):

Similar Species

Other Information


Polygonum arenastrum, also known as beach knotweed or silverweed, is a perennial herb native to Europe and Asia. It is found in sandy coastal habitats and can also be found in dunes, salt marshes and also on rocky shores. It is generally considered an invasive species in some areas and can be difficult to control once established. It has small green leaves and small white or pink flowers that bloom in the summer. It is often used as a traditional medicinal plant to treat various ailments such as wounds, burns and skin disorders.


Equal-leaved Knotgrass, scientifically known as Polygonum arenastrum, is a small annual plant that belongs to the Polygonaceae family. It is a common weed found in lawns, gardens, roadsides, and other disturbed areas across North America, Europe, and Asia.

The plant grows up to 15 cm in height and has a sprawling or prostrate growth habit. The leaves of the plant are alternate and simple, with an oval to lanceolate shape, and are generally around 1-2 cm long. The flowers are small, pinkish-white or greenish-white, and appear in small clusters at the leaf axils from June to September.

Equal-leaved Knotgrass is a resilient plant that can tolerate a wide range of growing conditions, from full sun to partial shade and various soil types. It is also drought-tolerant, making it a hardy species that can survive in harsh environments.

Despite being considered a weed, Equal-leaved Knotgrass has some benefits. It is a good source of nectar for bees and other pollinators, and its seeds are a food source for birds. In addition, the plant has some medicinal properties and has been used traditionally to treat various ailments, such as digestive issues, skin conditions, and respiratory problems.

Equal-leaved Knotgrass is easy to control and manage as it can be removed by hand or through regular mowing. However, if it is left to grow unchecked, it can form dense mats that can compete with other plants and reduce biodiversity.

Equal-leaved Knotgrass is also known by several other common names, including common knotgrass, wireweed, doorweed, and birdweed. The name "knotgrass" comes from the plant's prostrate habit and the fact that it often forms tangled mats that resemble knots.

The plant has a long history of use in traditional medicine. It was used by Native American tribes to treat diarrhea, stomachaches, and wounds. In Chinese medicine, it has been used to treat skin conditions, such as eczema and psoriasis, as well as respiratory infections and inflammation.

Equal-leaved Knotgrass also has some potential uses in modern medicine. Studies have shown that the plant contains compounds with anti-inflammatory, antioxidant, and antimicrobial properties. These compounds have been found to be effective in reducing inflammation and oxidative stress in the body, as well as inhibiting the growth of certain bacteria and fungi.

In addition to its medicinal properties, Equal-leaved Knotgrass has some practical uses. It has been used as a dye plant, with the leaves producing a yellow-green color when boiled in water. The plant has also been used as a source of food for humans and livestock, with the young leaves and shoots being edible when cooked.

Equal-leaved Knotgrass is also known for its ability to absorb heavy metals from contaminated soil. Studies have shown that the plant can accumulate high levels of metals, such as lead, cadmium, and copper, in its tissues. This makes it a useful tool for phytoremediation, a process in which plants are used to remove pollutants from soil or water.

In addition to its ecological and medicinal uses, Equal-leaved Knotgrass has also played a role in folklore and mythology. In European folklore, the plant was believed to have magical properties and was often used in love spells and charms. In Greek mythology, the plant was associated with Demeter, the goddess of agriculture and fertility, and was believed to have the power to increase fertility and abundance.

Despite its many uses and benefits, Equal-leaved Knotgrass is still considered a weed in many parts of the world. It can be a persistent problem in lawns and gardens, where it can quickly spread and become invasive. However, with proper management and control, it is possible to minimize its impact and appreciate its many virtues.

One interesting aspect of Equal-leaved Knotgrass is its adaptability to changing environmental conditions. It has been observed that the plant can rapidly adjust its growth patterns in response to changes in light and temperature, which allows it to thrive in a wide range of habitats. This adaptability may help to explain why the plant is so widespread and successful as a weed.

Equal-leaved Knotgrass has also been the subject of scientific research, particularly in the areas of ecology and plant biology. For example, studies have examined the plant's role in the ecosystem, including its interactions with pollinators, herbivores, and other plant species. Other studies have investigated the plant's genetic makeup and its ability to survive and reproduce under different conditions.

As with many other plant species, Equal-leaved Knotgrass faces a number of threats, including habitat loss, pollution, and climate change. However, its ability to adapt and thrive in changing environments may help it to persist in the face of these challenges.

In conclusion, Equal-leaved Knotgrass may be a common and often overlooked weed, but it has many fascinating qualities and potential uses. From its role in traditional medicine to its ability to absorb pollutants from soil, this unassuming plant has much to offer. As we continue to learn more about its ecology, biology, and potential benefits, we may discover even more reasons to appreciate this resilient and versatile species.

Distribution Map

Reproduced by kind permission of the BSBI.

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