Brazilian waterweed (Egeria densa) is a large-flowered plant that is native to South America, particularly Brazil, Uruguay, and Argentina. It is an invasive species in other areas due to the fact that people use it in aquariums and release it into non-native habitats.
I. Appearance and CharacteristicsÂ
Egeria densa, the large-flowered waterweed or Brazilian waterweed, is a species of Egeria native to warm temperate South America in southeastern Brazil, Argentina, Chile and Uruguay.
Egeria densa is an aquatic plant growing in water up to 4 m (13 ft) deep, with trailing stems to 2 m (6.6 ft) or more long, producing roots at intervals along the stem. The leaves are produced in whorls of four to eight, 1–4 cm (0.39–1.57 in) long and 2–5 mm (0.079–0.197 in) broad, with a pointed leaf tip. The stem system of the plant will grow until it reaches the surface of the water, where it will begin to spread out, creating a thick flower canopy that blocks light from reaching plants below it. It is dioecious, with male and female flowers on separate plants; the flowers are 12–20 mm (0.47–0.79 in) diameter, with three broad, rounded, white petals, 8–10 mm (0.31–0.39 in) long on male plants, and 6–7 mm (0.24–0.28 in) long on female plants.
Egeria densa typically displays little variation in growth patterns throughout the year when grown in tropical environments; however, when grown in more moderate environments the plant spends most of its energy on starch production and storage in the winter and canopy growth during the summer season.
It grows well in the cooler aquarium and is suitable for the beginner. It is easily propagated by cuttings. According to reports it secretes antibiotic substances which can help prevent blue-green algae. It grows best in a nutrient-rich, high light environment, but has shown an ability to outcompete other species when it is introduced.
Egeria densa has escaped from cultivation and become naturalized and invasive in many warm temperate to subtropical regions of the world, including Abkhazia, South Africa, the Azores, Guangdong, Hawaii, the Society Islands, Venezuela, New Zealand, New Caledonia, and North America. In the United States it occurs from New York south to Florida and west to California and Oregon. In the Sacramento-San Joaquin Delta of California, it was introduced in the 1960s and has since had a significant adverse impact on the local ecosystem. The plant currently infests 2,400 ha (5,900 acres), or 12% of the total surface area of the delta, along with other states and even as far north as Canada.
Recently, E. densa was reported as a naturalized alien species in Iceland where it invaded the naturally heated water bodies. Due to its occurrence in northern Iceland, E. densa is one of the first freshwater alien plant species that reached the Arctic. Most of its impact occurs in the shallow waterways; the plant forms thick mats that obstruct boat passage, clog water intakes and aqueducts, trap sediments, crowd out native vegetation, and impede the migration of anadromous fish.
II. How to Grow and Care
Sunlight
Brazilian waterweed thrives in full sun conditions, harnessing abundant light to facilitate robust growth and maintain optimal health. Exposure to intense light optimizes photosynthetic efficiency, essential for vigorous development. While Brazilian waterweed can endure a range of light intensities, deviations from its ideal luminosity may lead to reduced growth rates and potential compromise in vitality.
When grown outdoors, brazilian waterweed performs best when planted in locations that receive unfiltered sunlight for most of the day. Due to its preference for ample light, ensuring brazilian waterweed is positioned to capture maximum sunlight will support its lush, healthy formation.
Watering
Brazilian waterweed thrives in the submerged environments of warm temperate to tropical freshwater habitats, indicating its preference for consistent moisture. It is adept at managing periods of submersion, showing a resilience to varied water levels. This species requires watering every week to maintain its lush growth and health. As an aquatic plant commonly grown indoors, brazilian waterweed demonstrates a remarkable ability to oxygenate water, contributing significantly to the ecological balance within aquariums or ponds.
Fertilizing
For healthy growth and vigor, brazilian waterweed thrives with balanced nutrition fertilizers containing nitrogen (N), phosphorus (P), and potassium (K). Administer this fertilizer monthly at a quarter strength during the growing season, reducing frequency in colder months. Given brazilian waterweed’s aquatic habitat, apply liquid forms carefully to avoid water quality issues. Utilize special aquatic plant fertilizers to meet brazilian waterweed’s requirements without harming its environment. Always follow product guidelines to prevent over-fertilization, which can lead to algal blooms. A regular fertilization schedule ensures optimal growth and contributes to the aquatic ecosystem’s balance.
Propagation
This aquatic plant proliferates through stem cuttings, which root easily in suitable conditions. When a healthy stem is clipped below a node and planted in the substrate, it readily forms new roots. Internodal shoots will also grow when trimmed sections are left floating or anchored. This rapid growth requires monitoring to prevent brazilian waterweed from overwhelming aquatic spaces. Ensuring nutrient-rich water and adequate light will support robust growth. Frequent pruning maintains the plant’s density and vigor, encouraging lush underwater landscapes.
Transplanting
The prime window for relocating brazilian waterweed stretches from the warming embrace of late spring through to the heart of summer, offering robust growth potential. Choose luminous, aquatic environs and embrace planting fragments gently, ensuring a friendly nudge towards successful propagation.
III. Uses and BenefitsÂ
E. densa, like other macrophytes, are effective when used in wastewater treatment plants due to the same factors that make it a potential invasive plant; mainly its ability to uptake nutrients, and sedimentation of particles from the water column.
IV. How to Control
A variety of methods are needed to ensure that growth of E. densa is stopped due to its ability to regrow when fragmented through mechanical means. The best way is to remove the plant in entirety from the water column or use herbicides to kill the plant. One of the potential solutions to the problem are water drawdowns, as the plant is very sensitive to drying out and the plant can die in as short as an hour when removed from water. I
n addition cold weather has been found to be effective in controlling the plant, though this has practical limitations. When herbicides were applied to the plant, the levels of phosphorus and nitrogen increased but not greatly, suggesting that most of the nutrients remained in the plant biomass and did not reabsorb into the water column.