Brazilian waterweed

Invasive Species Information

Black current Biodiversity Medium Risk Invasive Species 14

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.

Black current Biodiversity Medium Risk Invasive Species 14

Brazilian waterweed flower and stem

Black current Biodiversity Medium Risk Invasive Species 14

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

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

Black current Biodiversity Medium Risk Invasive Species 14

Leaves

Black current Biodiversity Medium Risk Invasive Species 14

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.

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

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.

Non-Native Plant Species identified as High Risk on Ireland's Biodiversity List...

Environment 

Terrestrial

Freshwater

Terrestrial

Terrestrial

Marine

Freshwater

Freshwater

Freshwater

Terrestrial

Terrestrial

Terrestrial

Terrestrial

Marine

Terrestrial

Freshwater

Freshwater

Freshwater

Terrestrial

Freshwater

Marine

Risk score 

20

19

18

19

18

19

21

20

19

18

18

19

19

20

20

19

20

20

20

18

Additional Non-Native Plant Species identified as Medium Risk on Ireland's Biodiversity List...

Common name 

African woodsorrel

American skunk cabbage

Annual bur-sage

Antithamnionella ternifolia

Barberry

Black currant

Brazilian waterweed

Butterfly-bush

Canadian-fleabane

Clover broomrape

Creeping Bellflower

Dead man's fingers

Douglas fir

Early goldenrod

False acacia

Field penny-cress

Garden lupin

Giant rhubarb

Hairy rocket

Himalayan honeysuckle

Himalayan knotweed

Holm oak

Japanese barberry

Japanese honeysuckle

Japanese rose

Leafy spurge

Least duckweed

Narrow-leaved ragwort

New Zealand bur

Ostrich fern

Pampas grass

Pitcherplant

Red oak

Red sheath tunicate

Rock cotoneaster

Rum cherry

Russian-vine

Salmonberry

Sea-buckthorn

Sycamore

Three-cornered garlic

Traveler's-joy

Tree of heaven

Turkey oak

Virginia-creeper

Warty cabbage

Water fern

Wild parsnip

Environment 

Terrestrial

Terrestrial

Terrestrial

Marine

Terrestrial 

Terrestrial

Freshwater

Terrestrial 

Terrestrial 

Terrestrial 

Terrestrial 

Marine 

Terrestrial 

Terrestrial 

Terrestrial 

Terrestrial 

Terrestrial

Terrestrial

Terrestrial 

Terrestrial

Terrestrial

Terrestrial 

Terrestrial 

Terrestrial 

Terrestrial

Terrestrial 

Freshwater 

Terrestrial 

Terrestrial 

Terrestrial 

Terrestrial  

Terrestrial 

Terrestrial 

Marine 

Terrestrial 

Terrestrial 

Terrestrial

Terrestrial

Terrestrial

Terrestrial 

Terrestrial

Terrestrial 

Terrestrial 

Terrestrial 

Terrestrial 

Terrestrial 

Freshwater 

Terrestrial

Risk score 

14

15

17

15

14

14

17

17

14

17

16

16

15

14

17

17

17

16

17

14

16

14

14

15

14

16

14

16

14

14

14

14

14

14

14

17

14

14

14

15

15

17

17

14

16

15

14

15

© 2019 www,japaneseknotweedkillers.com  -  The Knotweed Removal Experts  -  Invasive Weed Specialists  -  Call +353 (0)86-250-8805