Brazilian waterweed
Invasive Species Information

What Is Brazilian waterweed - (Egeria densa)?

Habitat: Aquatic, fresh water
Distribution in Ireland: Sparse distribution but locally abundant in some places.

Status: Established

Family name: Hydrocharitaceae

Common name/s: Large-flowered waterweed, Dense waterweed, Anacharis

Reproduction: 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. Can spread through transport of plant fragments.

Brazilian waterweed flower and stem

Brazilian waterweed leaf

Brazilian Waterweed is an Aquatic plant native to Argentina, Brazil, and Uruguay, growing in water up to 4 m deep, with trailing stems to 2 m or more long, producing roots at intervals along the stem.

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.

Brazilian waterweed, or Egeria densa, Perennial, floating or rooted. Elongate stems bear leaves in densely spaced whorls of 4-5 (particularly dense near apex). Leaves scale-like, sessile, linear, slightly recurved, with single mid-vein; margin finely serrate. Inflorescence axillary, of unisexual flowers. Female and male flowers similar in shape, opening above water surface; sepals 3; petals 3, white. Dispersal by seed and stem fragments.

Adventitious roots (unbranched) and lateral branches grow only from double nodes (specialized nodes separated by a shortened internode) typically spaced along stems at 6-12 node intervals. Only fragments containing a double node develop into new plants.

Egeria densa is often confused with other waterweeds such as; Elodea, Hydrilla, Lagarosiphon.

Brazilian waterweed can grow as a floating plant or anchored in the substrate. It can grow under almost any conditions, growing vigorously when in colder temperatures and hard water rich in calcium, however, it tolerates higher temperatures for a short time without slowing growth. Growth is slower in soft water areas. Brazilian waterweed does not require CO2 fertilisation, however, the presence of CO2 will speed up growth.

How To Identify Brazilian waterweed?

Brazilian waterweed - Egeria densa ID Guide

Leaf: Very fine toothed whorled green leaf 4-8 and 1-4 cm long with pointed tip
Flower: white with 3 petals and yellow stamen appear along stems, can grow up to 4m deep

Leaves

Flower

Why Is Brazilian waterweed A Problem?

Out competes native species. 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.

Brazilian waterweed Invasive Species Information

How To Identify Brazilian waterweed?

European Communities (Birds and Natural Habitats) Regulations 2011 non-native invasive plant species A-Z (Updated 2017)

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There are currently 35 invasive plant species listed in the European Communities (Birds and Natural Habitats) Regulations (annex 2, Part 1)...

Click on a species from the following list to find out more regarding non-native species subject to restrictions under Regulations 49 and 50.

American Skunk-Cabbage - Lysichiton americanus

Brazilian waterweed
Invasive Species Information