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Square-stemmed Willowherb

Epilobium tetragonum

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Plant Profile

Flowering Months:
Onagraceae (Willowherb)
Life Cycle:
Maximum Size:
130 centimetres tall
Ditches, gardens, grassland, hedgerows, riversides, rocky places, wasteland, waterside, wetland, woodland.

Pink, 4 petals
Purplish-pink flowers, up to 8mm in diameter. 4 notched petals. White club-shaped stigma.
Long, slender, cylindrical fruit capsules, up to 10cm long.
Narrow, small-toothed, strap-shaped leaves. Shiny and unstaked. The downy stems are conspicuously square in cross-section making this species easy to identify. Perennial.
Other Names:
Square-stalked Willowherb, Squarestem Willowherb.
Frequency (UK):

Other Information


Epilobium tetragonum, also known as squarestem willowherb, is a species of willowherb in the family Onagraceae. It is native to North America and is commonly found in dry, rocky or sandy habitats. The plant is a perennial herb with square stems and small, four-angled leaves. The flowers are pink to purplish and are typically found in clusters at the tips of the stems. It is also known to grow as a weed in some places.


Square-stemmed Willowherb, also known as Epilobium tetragonum, is a species of flowering plant that is commonly found in the Northern Hemisphere, particularly in North America and Europe. This herb is a member of the Onagraceae family and is known for its distinctive square stems, narrow leaves, and clusters of pink or white flowers that bloom in the summer.

The Square-stemmed Willowherb is a hardy and adaptable plant that can grow in a variety of habitats, including meadows, wetland margins, and disturbed areas. It prefers moist soils and is often found along streams, rivers, and ditches. This plant is also well-known for its ability to colonize areas that have been disturbed by human activity, such as road and railway verges, and is therefore considered an invasive species in some regions.

One of the most notable features of the Square-stemmed Willowherb is its attractive flowers, which are usually pink or white and are produced in large clusters. These flowers are an important source of nectar for many pollinators, including bees, butterflies, and hummingbirds, making the plant an important part of the local ecosystem.

In addition to its ornamental value, Square-stemmed Willowherb has a long history of medicinal use. The plant has been used to treat a variety of ailments, including skin irritations, wounds, and digestive problems. Its anti-inflammatory and analgesic properties have been documented in traditional medicine, and it has been used as a natural remedy for centuries.

Despite its widespread distribution, Square-stemmed Willowherb is considered a threatened species in some areas due to habitat loss and degradation. As more and more land is developed and converted for human use, the natural habitats of this and many other plant species are being destroyed, leading to declines in populations.

The Square-stemmed Willowherb is a fascinating plant with a rich history of medicinal use and ecological importance. Its hardiness and ability to thrive in disturbed areas make it a valuable species for conservation and ecological restoration efforts. Whether you are a nature lover, a gardener, or simply someone who appreciates the beauty of the natural world, this herb is definitely worth taking the time to learn more about.

In addition to its ecological and medicinal benefits, Square-stemmed Willowherb is also a valuable species for study in botany and ecology. Scientists have studied the plant's reproductive biology, genetics, and its interactions with other species in the ecosystem. For example, researchers have found that the plant's ability to grow in disturbed areas is due to its ability to produce large amounts of seeds that can be dispersed easily by wind or water.

Another interesting aspect of Square-stemmed Willowherb is its distribution and range. The plant is widely distributed throughout the Northern Hemisphere and has been introduced to other regions as a result of human activity. This has led to the plant becoming an invasive species in some areas, where it can outcompete native plants and alter local ecosystems.

Despite its invasive nature in some regions, Square-stemmed Willowherb can also play a positive role in the rehabilitation of disturbed areas. For example, the plant can help to stabilize soil and prevent erosion, which can be particularly beneficial in areas that have been subjected to mining or other forms of land disturbance. Additionally, the plant's ability to grow in disturbed areas can help to provide habitat and food for wildlife, helping to restore the balance of the local ecosystem.

The Square-stemmed Willowherb is a fascinating and important species that deserves our attention and appreciation. Whether you are interested in its ornamental value, medicinal properties, or ecological significance, this herb is a valuable component of the natural world that should be protected and preserved for future generations.

It is also worth mentioning that Square-stemmed Willowherb is a versatile plant that is well-suited for cultivation in gardens and landscapes. The plant's attractive flowers and hardy nature make it a popular choice for wildflower gardens, meadows, and other naturalistic landscapes. The plant is also easy to grow and is low maintenance, making it a great choice for gardeners who want to incorporate native species into their landscapes.


Square-stemmed Willowherb filmed at Hic Bibi Local Nature Reserve in Coppull, Lancashire on the 7th June 2023.


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Distribution Map

Reproduced by kind permission of the BSBI.

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