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Opposite-leaved Pondweed

Groenlandia densa

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:
150 centimetres long
Ditches, gardens, ponds, water.

Green, 4 petals
A short flower spike.
Roundish fruit with a hooked beak, up to 3mm long.
Opposite or whorled, undivided leaves. Wavy, toothed, narrowly oblong leaves. Opposite-leaved Pondweed is similar in appearance to Curled Pondweed (Potamogeton crispus) but Opposite-leaved Pondweed has shorter, wavy leaves. Perennial.
Frequency (UK):

Similar Species

Other Information


Opposite-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 opposite to each other, lanceolate 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.


Opposite-leaved Pondweed, also known by its scientific name Groenlandia densa, is a common aquatic plant found in ponds, lakes, and slow-moving streams throughout North America, Europe, and Asia. It is a perennial herbaceous plant that is easily recognized by its opposite, linear, and narrow leaves that are arranged in whorls around the stem.

The plant's stem can grow up to 1.5 meters long and can be either floating or submerged, depending on the depth of the water. The leaves are typically 2-3 cm long and 1-2 mm wide, and they have a distinctive yellow-green color. The plant's flowers are small and inconspicuous, and they bloom from June to September.

Opposite-leaved Pondweed is an important plant for aquatic ecosystems, as it provides a habitat for many aquatic animals, including fish, amphibians, and invertebrates. The plant's dense growth also helps to stabilize the bottom sediments of ponds and lakes, preventing erosion and improving water quality.

In addition to its ecological benefits, Opposite-leaved Pondweed has also been used for medicinal purposes. The plant's leaves and stems contain a variety of compounds, including tannins, flavonoids, and alkaloids, that have been found to have anti-inflammatory, antioxidant, and analgesic properties. In traditional medicine, the plant has been used to treat a variety of ailments, including arthritis, rheumatism, and menstrual cramps.

Despite its ecological and medicinal importance, Opposite-leaved Pondweed can also be considered a nuisance in some situations. The plant can grow rapidly, forming dense mats that can interfere with recreational activities such as swimming and boating. In addition, the plant's growth can be a problem in aquaculture operations, where it can interfere with the growth and development of fish.

Opposite-leaved Pondweed, like many aquatic plants, is also an important indicator of water quality. It is highly sensitive to changes in water chemistry and nutrient levels, making it a useful tool for monitoring water quality in lakes and streams. In fact, the presence or absence of Opposite-leaved Pondweed can be used as an indicator of a healthy or degraded ecosystem.

In addition to its ecological and medicinal benefits, Opposite-leaved Pondweed also has cultural significance. The plant has been used by Indigenous communities in North America for a variety of purposes, including as a food source, a medicine, and a material for making baskets and other woven items.

Opposite-leaved Pondweed also has a role in modern conservation efforts. In some areas, the plant has been listed as a threatened or endangered species due to habitat loss and degradation. Efforts are underway to protect and restore populations of Opposite-leaved Pondweed and other aquatic plants, which are critical for maintaining healthy aquatic ecosystems.

One interesting aspect of Opposite-leaved Pondweed is its ability to adapt to changing environmental conditions. Like many aquatic plants, it can adjust its growth and metabolism in response to changes in temperature, light, and nutrient availability. This allows it to survive in a wide range of aquatic habitats, from shallow ponds to deep lakes.

Opposite-leaved Pondweed is also capable of reproducing both sexually and asexually. Sexual reproduction occurs through the production of small flowers that are pollinated by waterborne pollen. Asexual reproduction occurs through the formation of vegetative propagules, which are new plants that grow from the stem or root of the parent plant. This ability to reproduce both sexually and asexually allows Opposite-leaved Pondweed to rapidly colonize new areas and adapt to changing environmental conditions.

It is worth noting that Opposite-leaved Pondweed is just one of many important aquatic plants found in freshwater ecosystems. Other common aquatic plants include Watermilfoil, Waterweed, and Duckweed, each of which has its own unique set of ecological and cultural benefits. By studying and protecting these plants, we can ensure the continued health and vitality of our freshwater ecosystems, and the many species that rely on them for survival.

One of the major threats to Opposite-leaved Pondweed and other aquatic plants is the introduction of invasive species. Invasive species are non-native species that are introduced into an ecosystem and can outcompete native species for resources. This can lead to a decline in native plant and animal populations, as well as a decrease in overall ecosystem health.

One example of an invasive species that can be particularly harmful to aquatic plants is Eurasian Watermilfoil (Myriophyllum spicatum). Eurasian Watermilfoil is a fast-growing aquatic plant that can form dense mats and outcompete native plant species. It can also interfere with water flow, block sunlight, and decrease dissolved oxygen levels, which can harm fish and other aquatic animals.

To combat the spread of invasive species, it is important to take steps to prevent their introduction and to control their spread once they have become established. This can include measures such as boat inspections, control of waterfowl and other animals that may carry invasive species, and the use of herbicides and other control methods.

Overall, Opposite-leaved Pondweed is an important and fascinating plant that plays a critical role in freshwater ecosystems. By studying and protecting this and other aquatic plants, we can ensure the continued health and vitality of our freshwater ecosystems and the many species that depend on them.

Distribution Map

Reproduced by kind permission of the BSBI.

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