Brazilian waterweed

Appearance

''Egeria densa'' is an aquatic plant growing in water up to 4 m deep, with trailing stems to 2 m or more long, producing roots at intervals along the stem. The leaves are produced in whorls of four to eight, 1–4 cm long and 2–5 mm 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 diameter, with three broad, rounded, white petals, 8–10 mm long on male plants, and 6–7 mm long on female plants.

Naming

''Egeria densa'' has escaped from cultivation 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. 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 , 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 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.

Behavior

''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

Uses

''Egeria densa'' is a popular aquarium plant, but is no longer sold in some areas due to its invasive potential. Plants in cultivation are all a male clone, reproducing vegetatively.

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.