Common name: Large-flowered Waterweed, Brazilian Waterweed, Elodea, Anachris
Synonymus: Anacharis densa (Planch.) Vict., Elodea densa (Planch.) Casp
Distribution and habitat: Egeria densa is an ageless aquarium plant, a species of Egeria native to warm temperate South America in southeastern Brazil, Argentina, and Uruguay and become naturalized and invasive in many warm temperate to subtropical regions of the world, including Europe, southern Africa, Asia, Australia, New Zealand and North America.
Description: It is an aquatic plant growing in water up to 4m (13 feet) deep, with trailings stems to 2m (6 feet) or more long, producing roots at intervals along the stem. The leaves are produced in whorls of four to eight, 1–4cm (0.3-1.5 inch) long and 2–5mm (0.7-2 inch) broad, with an acute apex. It is dioecious, with male and female flowers on separate plants; the flowers are 12–20mm (0.4-0.8 inch) diameter, with three broad, rounded, white petals, 8–10mm (0.3-0.4 inch) long on male plants, and 6–7mm (0.2 inch) long on female plants.
Houseplant care: Must be planted in full sun to avoid the lower leaves from rotting, submerged at the base of a waterfall where the water moves freely is ideal providing excellent filtration. It will not do well in still waters. It grows best in a nutrient rich, high light situation.
Egeria densa is an adaptable plant that can grow in both high light and low light conditions. When grown in high light, Egeria densa stems will display a dark green and grow up to 0.5m (2 feet) long in a short matter of time. It will appear very leaf due to the short distance between the internodes of the stem. In low light situations, the leaves and internodes along the stem will become more spaced out, the stem becomes thinner, and the plant will take on a dull green color.
Temperature: It grows well in the cooler aquarium and is very easy to grow.
Propagation: It is easily propagated through fragmenting the stem and side shoots. Plants in cultivation are all a male clone, reproducing vegetatively.
Uses: Egeria densa is a popular aquarium plant. Egeria densa is used to oxygenate the water and to absorb excess nutrients.
Egeria densa can be used in the background or midground areas of sparsely planted aquariums planted in bunches of 6-7 stems. It also does well floating.
It said that Egeria densa secretes anti-bacterial enzyme that can reduce blue-green algae (cyanobacteria).
It is often confused with similar looking species Hydrilla and Elodea Canadensis as per image bellow:
Egeria densa leaves are in whorls (leaf groups) of 4 to 5; Hydrilla leaves are in whorls of 4 to 8; and Elodea Canadensis forms whorls of 3.
Note: The rapid growing nature, couple with few predators and no diseases, has allowed Egeria densa to flourish in the wild unchecked. Ponds, lakes and streams are in danger to become infected, large mats of Egeria densa that prosper block out the sun to the native vegetation, causing havoc on the local ecosystem and boaters. Take great care not to let this plant enter local waterways.
Hardiness zone: 5a-11