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Slender-leaved Pondweed

Potamogeton filiformis

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:
Potamogetonaceae (Pondweed)
Life Cycle:
Maximum Size:
1 metre long
Ditches, gardens, mud, ponds, seaside, water.

Green, 4 petals
Green flowers spikes which are spread out in flower.
Almost spherical, yellowish-green, up to 5mm long and 4mm wide.
Dark green, rounded, linear, bootlace-type leaves with blunt tips. The stems are flattened. Unlike the similar looking and taller Fennel Pondweed (Potamogeton pectinatus), the stipules are not white-edged and the stems are more branched. Often seen growing in tufts.
Other Names:
Narrow-leaved Pondweed, Thread-leaved Pondweed.
Frequency (UK):

Similar Species

Other Information


Potamogeton filiformis, also known as thread-leaved pondweed, is a perennial aquatic plant that is native to North America. It is commonly found in freshwater ponds, lakes, rivers, and streams. The leaves are long, thin, and typically float on the water's surface, they are thread-like in shape, with smooth edges. The stems are long, thin, and anchored to the bottom by rhizomes. The flowers are small and inconspicuous, and arranged in spikes at the top of the stem. They typically bloom in late spring to early summer. It is an important food source for waterfowl and aquatic animals, and it also provides cover and habitat for fish and other aquatic organisms. It's considered a good oxygenator for the aquatic ecosystem and it's also used as an ornamental plant in water gardens and ponds.


Slender-leaved pondweed, also known by its scientific name Potamogeton filiformis, is a submerged aquatic plant that is found in ponds, lakes, and slow-moving streams across much of North America. It is a member of the Potamogetonaceae family, which includes other pondweeds like curly-leaf pondweed and variable-leaf pondweed.

Appearance and Identification

Slender-leaved pondweed is a relatively small plant, growing to only about 3 feet in length. It has long, thin leaves that are often less than a quarter inch wide, giving it its characteristic "slender" appearance. The leaves are typically green, but can sometimes have a reddish or purplish tint. They are arranged in an alternate pattern along the stem.

The stem of the plant is also thin and flexible, allowing it to bend and sway with the movement of the water. The plant produces small, inconspicuous flowers that are arranged in a spike-like inflorescence that emerges from the water's surface.

Habitat and Ecology

Slender-leaved pondweed is a highly adaptable plant that can grow in a variety of aquatic habitats. It is commonly found in shallow water with a substrate of sand, silt, or gravel, but can also grow in deeper water. The plant prefers nutrient-rich water, but can also tolerate nutrient-poor conditions.

Slender-leaved pondweed plays an important role in aquatic ecosystems as a food source for waterfowl, fish, and invertebrates. It also helps to oxygenate the water and provide habitat for aquatic animals.

In some cases, however, slender-leaved pondweed can become invasive and outcompete native aquatic plants, leading to a decrease in biodiversity and a disruption of the ecosystem.

Uses and Benefits

Slender-leaved pondweed has been used for a variety of purposes throughout history. Native Americans used the plant for medicinal purposes, such as treating skin ailments and digestive problems. It was also used as a food source, with the young leaves and stems being eaten raw or cooked.

Today, slender-leaved pondweed is primarily used as an ornamental plant in water gardens and aquariums. Its slender, delicate appearance makes it a popular choice for creating a natural-looking aquatic environment.

Conservation and Management

Slender-leaved pondweed is not considered a threatened or endangered species, but like many aquatic plants, it is vulnerable to habitat loss and degradation. It is important to protect the natural habitats where the plant is found and to manage invasive species that can threaten its survival.

In addition, landowners and aquatic resource managers can take steps to promote the growth of slender-leaved pondweed and other native aquatic plants, such as reducing nutrient inputs into water bodies, controlling erosion, and maintaining healthy aquatic ecosystems.

Slender-leaved pondweed is a small but important aquatic plant that plays a critical role in supporting the health and diversity of aquatic ecosystems. While it is not without its challenges, managing and conserving the plant and its habitat can help to ensure that it continues to thrive in North America's waterways.

More Information

Slender-leaved pondweed is a fascinating plant that is well-suited to life in aquatic environments. It has a number of adaptations that allow it to thrive in water, such as its flexible stem that allows it to move with the current and its long, thin leaves that maximize the plant's surface area for photosynthesis.

One interesting fact about slender-leaved pondweed is that it is able to reproduce both sexually and asexually. The plant produces small, inconspicuous flowers that are pollinated by water or wind. It can also reproduce vegetatively, with new plants growing from fragments of the parent plant.

Despite its importance to aquatic ecosystems, slender-leaved pondweed is not without its challenges. Invasive species like Eurasian watermilfoil and curly-leaf pondweed can outcompete the plant for resources and reduce its ability to grow and reproduce. In addition, human activities like nutrient pollution and shoreline development can degrade the quality of aquatic habitats and threaten the survival of the plant.

Efforts to manage and conserve slender-leaved pondweed and other native aquatic plants can help to protect the health and biodiversity of our waterways. This can include actions like reducing nutrient inputs into water bodies, controlling the spread of invasive species, and promoting healthy aquatic ecosystems. With careful management and conservation, we can ensure that slender-leaved pondweed continues to thrive in North America's lakes, ponds, and streams for generations to come.

Another interesting aspect of slender-leaved pondweed is its ecological role in aquatic food webs. As a primary producer, it is an important source of food for a variety of aquatic animals, including waterfowl, fish, and invertebrates. In turn, these animals become food for larger predators, creating a complex web of relationships within aquatic ecosystems.

Slender-leaved pondweed also helps to oxygenate the water, which is essential for the survival of aquatic animals. Through photosynthesis, the plant produces oxygen that is released into the water, providing a critical resource for fish and other organisms.

In addition, slender-leaved pondweed can play an important role in preventing erosion and stabilizing shorelines. Its roots help to hold sediment in place, reducing the impact of waves and currents on the shoreline. This can help to prevent the loss of valuable habitat for aquatic animals and plants.

Slender-leaved pondweed can also be used as a bioindicator, a species that can be monitored to assess the health of aquatic ecosystems. The presence or absence of slender-leaved pondweed in a water body can provide important information about the quality of the water and the overall health of the ecosystem. For example, if slender-leaved pondweed is absent or declining in a particular area, it may be an indication of habitat degradation, pollution, or the presence of invasive species.

In addition to its ecological and environmental importance, slender-leaved pondweed has cultural and historical significance as well. It has been used for centuries by indigenous peoples in North America for medicinal and culinary purposes. The plant contains high levels of vitamin C and was traditionally used to treat a variety of ailments, such as colds, fevers, and infections. The young leaves and stems were also eaten raw or cooked as a source of food.

Today, slender-leaved pondweed is mainly used in ornamental settings, such as water gardens and aquariums. Its delicate appearance and adaptability to different water conditions make it a popular choice for creating natural-looking aquatic environments. However, it is important to source slender-leaved pondweed ethically and avoid collecting plants from the wild, which can disrupt natural ecosystems and contribute to the decline of the species.

In conclusion, slender-leaved pondweed is a fascinating and important aquatic plant that plays a critical role in supporting the health and diversity of aquatic ecosystems. Through careful management, conservation, and responsible use, we can ensure that this species continues to thrive and contribute to the beauty and functionality of our waterways.

Distribution Map

Reproduced by kind permission of the BSBI.

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