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Large-flowered Waterweed

Egeria 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:
Hydrocharitaceae (Naiad)
Life Cycle:
Maximum Size:
4 metres long
Ditches, ponds, water, wetland.

White, 3 petals
Rarely flowering. Flowers are large compared to other Waterweed species. The petals are broad and rounded in shape, up to 2cm wide.
Fruits rarely appear.
Linear, pointed leaves in whorls of 4 to 8. The leaves are broader than other Waterweeds and have a pointed tip. Grows mainly in canals.
Other Names:
Brazilian Waterweed.
Frequency (UK):
Rarely seen  

Other Information


Egeria densa, also known as large-flowered waterweed or Brazilian waterweed, is a species of aquatic plant in the waterweed family. It is native to warm temperate South America, specifically southeastern Brazil. It is a good plant for aquariums, as its rapid growth helps to create balance and can prevent algal growth. It can also be used as a food source for fish, as it has high levels of proteins and carbohydrates.


Large-flowered Waterweed (Egeria densa) is a freshwater aquatic plant species that belongs to the Hydrocharitaceae family. It is native to South America but has been introduced to many parts of the world, including Europe, North America, and Australia, as an ornamental plant for aquariums and decorative ponds.

Egeria densa is a fast-growing, aquatic perennial that forms dense underwater stands. The leaves are long, narrow, and bright green, and are arranged in opposite pairs along the stem. The plant produces spikes of delicate, white flowers that rise above the water surface, giving the plant its common name, Large-flowered Waterweed.

Despite its popularity as an ornamental plant, Egeria densa is considered an invasive species in many parts of the world. It has the ability to rapidly outcompete native aquatic vegetation, and can form dense mats of vegetation that can impede water flow, alter water chemistry, and impact aquatic animal populations. In some cases, the plant can cause economic harm by clogging irrigation systems, reducing recreational activities, and reducing fish populations.

To control Egeria densa populations, various methods are used, including chemical treatments, manual removal, and biological control. Chemical treatments can be effective, but they can also be harmful to the aquatic ecosystem, so they must be applied with care. Manual removal involves physically removing the plant and its roots, but this can be time-consuming and costly. Biological control involves the use of a herbivorous insect that feeds exclusively on Egeria densa, reducing its populations without causing harm to other aquatic species.

Large-flowered Waterweed (Egeria densa) is a beautiful but invasive aquatic plant that can have negative impacts on aquatic ecosystems. It is essential to understand the potential harm it can cause and to control its populations using appropriate methods, such as biological control, to minimize its impacts.

geria densa has a high growth rate, and it can quickly form dense stands in ponds, lakes, and rivers. The plant produces large amounts of organic matter, which contributes to an increase in water turbidity and a decrease in oxygen levels, which can negatively impact the growth of other aquatic plants and the survival of aquatic animals.

In addition, Egeria densa can also alter the water chemistry by increasing the levels of nitrogen and phosphorus, which can lead to an increase in algal growth and a decline in water quality. This, in turn, can reduce the biodiversity of aquatic ecosystems, which can have far-reaching impacts on the entire food chain.

Egeria densa also poses a threat to water-based recreation, such as swimming, fishing, and boating. The dense mats of vegetation can obstruct waterways, making it difficult for boats and other watercraft to navigate, and the plant can also clog up swimming areas, making them unpleasant and unsafe for humans.

To prevent the spread of Egeria densa, it is important to take measures to prevent its introduction and spread in new areas. This can include inspecting boats and equipment before and after use in water bodies and disposing of plant material properly. It is also essential to educate people about the potential harm that the plant can cause and to encourage them to avoid planting and spreading it.

Egeria densa is a highly invasive species that has the potential to cause significant harm to aquatic ecosystems. It is essential to understand the potential impacts of the plant and to take measures to prevent its spread and control its populations. Through a combination of education, control measures, and responsible use of water resources, we can help protect our aquatic ecosystems and preserve their biodiversity for future generations.

It is important to note that Egeria densa is not only a threat to aquatic ecosystems, but it can also have impacts on adjacent terrestrial ecosystems. The dense mats of vegetation can provide ideal breeding habitats for mosquitoes, which can increase the risk of mosquito-borne diseases such as West Nile virus and dengue fever.

Furthermore, the impacts of Egeria densa can also extend to the economy. In some regions, the plant can reduce the value of real estate and the tourism industry by reducing the aesthetic value of water bodies and reducing recreational opportunities. In addition, the plant can also reduce the value of commercial and sport fisheries by reducing the abundance and diversity of fish populations.

To effectively manage Egeria densa populations, it is essential to adopt an integrated approach that combines multiple control methods, such as physical removal, chemical treatments, and biological control. In some cases, it may also be necessary to implement regulatory measures, such as the banning of the sale and distribution of the plant, to prevent its spread and introduction into new areas.

In conclusion, Egeria densa is a highly invasive species that has the potential to cause significant harm to aquatic and terrestrial ecosystems and the economy. It is essential to take measures to prevent its spread, control its populations, and minimize its impacts. Through cooperation and collaboration among stakeholders, we can protect our water resources and ensure their long-term sustainability.