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Fennel Pondweed

Potamogeton pectinatus

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:
3 metres long
Ditches, gardens, ponds, water, wetland.

Green, 4 petals
Compact flower spikes, usually submerged although occasionally are aerial. Water pollinated, inconspicuous flowers.
Yellowish-brown fruit. About 3 to 5mm long and 2 to 4mm wide. The seeds float on the surface of the water.
A fully submerged aquatic plant with rounded, leathery, bootlace-type leaves. Up to 4mm in diameter. Dark green, pointed, linear leaves with white-edged stipules. Perennial.
Other Names:
Duck Grass, Duck Moss, Fennel-leaved Pondweed, Potato Moss, Ribbon Weed, Sago Pondweed.
Frequency (UK):
Occasionally seen  

Similar Species

Other Information


Potamogeton pectinatus, also known as sago pondweed or fennel-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 lanceolate in shape, with smooth edges and have a distinctive comb-like or pectinate margins. 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.


Fennel Pondweed, scientific name Potamogeton pectinatus, is a submerged aquatic plant that is native to North America, Europe, and Asia. It is commonly found in shallow freshwater habitats such as ponds, lakes, and slow-moving streams. Fennel Pondweed is a valuable component of these ecosystems, providing food and shelter for aquatic organisms, while also improving water quality.

Description and Habitat

Fennel Pondweed is a perennial aquatic plant that has long, slender, and branching stems. The stems can grow up to 3 meters in length and are typically anchored to the bottom of the water body by a root system that is embedded in the sediment. The leaves of Fennel Pondweed are narrow, linear, and about 2 to 5 centimeters long. They are arranged alternately along the stem and have a distinctive wavy or crimped margin. The plant also produces small, inconspicuous flowers that are found on a spike at the base of the leaves.

Fennel Pondweed can grow in a wide range of aquatic habitats, from shallow ponds to deep lakes. It is typically found in areas where the water is clear and nutrient-rich. The plant prefers to grow in alkaline or neutral water and can tolerate moderate levels of salinity.

Ecological Importance

Fennel Pondweed is an important component of aquatic ecosystems, providing numerous ecological services. One of its main functions is to improve water quality by removing excess nutrients from the water column. The plant is capable of absorbing and storing large amounts of nitrogen and phosphorus, which are two of the main nutrients that contribute to eutrophication in freshwater systems. By removing these nutrients, Fennel Pondweed helps to prevent algal blooms and maintains water clarity, which is important for the survival of other aquatic plants and animals.

In addition to its role in nutrient cycling, Fennel Pondweed provides food and habitat for a wide range of aquatic organisms. The plant's leaves and stems are an important food source for many species of aquatic invertebrates, such as snails, insects, and crustaceans. These invertebrates, in turn, are preyed upon by fish and other aquatic predators, which rely on Fennel Pondweed as a source of food and shelter.

Conservation and Management

Despite its ecological importance, Fennel Pondweed is not considered a threatened species. However, like many aquatic plants, it is vulnerable to habitat destruction and water pollution. Human activities such as shoreline development, dredging, and nutrient runoff can have negative impacts on the plant and its associated aquatic communities. Therefore, it is important to manage and protect freshwater ecosystems to ensure the survival of Fennel Pondweed and other aquatic plants and animals.

Fennel Pondweed is a valuable and important component of freshwater ecosystems. Its ability to remove excess nutrients from the water column and provide food and habitat for aquatic organisms makes it a critical species for the maintenance of healthy and productive aquatic systems. Conservation efforts should focus on protecting and restoring habitats where Fennel Pondweed occurs to ensure its continued survival and contribution to freshwater ecosystems.

More Information

Fennel Pondweed has been traditionally used for medicinal purposes by indigenous peoples in North America. The plant was used to treat a variety of ailments, including respiratory and digestive disorders. Recent research has also shown that Fennel Pondweed may have potential as a natural remedy for hypertension and other cardiovascular diseases.

The plant is also popular among hobbyists and enthusiasts of aquascaping, which is the art of designing and creating aesthetically pleasing aquatic environments. Fennel Pondweed's long and slender stems, along with its wavy leaves, make it a popular choice for creating natural-looking aquascapes in aquariums and other aquatic displays.

Fennel Pondweed is also a valuable plant for ecological restoration projects. The plant's ability to remove excess nutrients from the water column makes it an effective tool for improving water quality in degraded aquatic systems. Restoration practitioners often use Fennel Pondweed as part of their efforts to restore degraded wetlands, streams, and lakes.

One of the interesting features of Fennel Pondweed is its ability to produce a dormant bud known as a turion. Turions are specialized structures that form at the base of the plant's stem and allow it to survive harsh winter conditions or periods of drought. The turion is an adaptive strategy that allows the plant to conserve energy and resources during times of stress and resume growth when conditions improve.

Fennel Pondweed is also important for its role in carbon sequestration. Like other aquatic plants, it absorbs carbon dioxide from the atmosphere during photosynthesis and stores it in its tissues. This carbon storage helps to mitigate the effects of climate change by reducing the amount of carbon dioxide in the atmosphere.

Finally, Fennel Pondweed is a fascinating subject for scientific research. Scientists study the plant to better understand its ecology, physiology, and biochemistry. The plant's ability to remove excess nutrients from the water column has implications for water management and environmental policy. Understanding the mechanisms by which Fennel Pondweed performs this function can help inform strategies for improving water quality in degraded aquatic systems.

In conclusion, Fennel Pondweed is an important and versatile aquatic plant with many ecological and economic benefits. Its ability to improve water quality, provide habitat and food for aquatic organisms, and sequester carbon makes it a valuable component of freshwater ecosystems. As we continue to face challenges such as climate change and water pollution, understanding and protecting species like Fennel Pondweed will be critical to ensuring the health and resilience of our natural systems.

Distribution Map

Reproduced by kind permission of the BSBI.

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