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Brazilian Waterweed - Egeria densa
State Rank Reason (see State Rank above)
Egeria densa is not known to occur in Montana. The Montana Department of Agriculture (MDA) classifies it as a Priority 3-Regulated Plant, which means it may not be intentionally spread or sold other than as a contaminant in agricultural products (MDA 2017). It is not a Montana listed noxious weed (MDA 2017). The purpose of this profile is to provide awareness and education. Brazilian Waterweed is native to Brazil (FNA 2000).
It was introduced into portions of the U.S. from eastern South America (DiTomaso and Healy 2003). It is sold as an aquarium décor under the name Egeria or Anacharis, and if released into lakes, ponds, or other waterways it can naturalize (DiTomaso and Healy 2003). This plant is also commonly used in introductory botany courses (FNA 2000).
PLANTS: Aquatic perennials that grow rooted in the substrate, but easily fragment. Only male plants are found in the U.S. (DiTomaso and Healy 2003).
LEAVES: Leaves are sessile and whorled in groups of 3-6(8) (DiTomaso and Healy 2003). Middle and upper leaves are 15-40 mm long, and 2-5 mm wide. Below the growing tips, leaves often curve downward. The lower surface of each leaf vein may be smooth or minutely and sharply toothed.
INFLORESCENCE: 1-flowered and sessile on stem with spathes (leaf-like bract) (FNA 2000). Male and female flowers occur on different plants (FNA 2000). Flowers are common and have 3 white petals. The female flowers have pistils each with 3 styles. The male spathes are 2-4 flowered, of 7.5-12 mm long, and pedicels of 80 mm long (FNA 2000).
Flowers summer to fall. Male and female flowers are separate and may extend up to 3 cm above the water’s surface (DiTomaso and Healy 2003). A singular female flower grows from a leaf axil, developing a long hypanthium tube, to reach the water’s surface (DiTomaso and Healy 2003).
The native Elodea canadensis has dark green leaves that are often speckled with large dark cells (DiTomaso and Healy 2003). Middle and upper leaves are opposite or 3-whorled and those below the growing tips often slightly curve downward (DiTomaso and Healy 2003). Leaves are often relatively longer (5-12 mm) and narrower (1.5-2.5 mm) in comparison to exotic species. The mid-vein of each leaf is smooth on its underside (DiTomaso and Healy 2003).
The exotic Hydrilla verticillata also have whorled leaves, but in groups of 3-12 that are 6-20 mm long and 1-4 mm wide (DiTomaso and Healy 2003). Leaves below the growing tips often curve downward (DiTomaso and Healy 2003). The mid-vein of each leaf is smooth or minutely toothed on its underside (DiTomaso and Healy 2003).
In the U.S. Brazilian Waterweed has been documented in the northeast, southeast, south-central, southwest, and Pacific coastal states of the lower 48. It is also documented in Idaho (Consortium of Pacific Northwest Herbaria).
For maps and other distributional information on non-native species see:
Nonindigenous Aquatic Species Database from the U.S. Geological Survey
Invasive Species Habitat Tool (INHABIT) from the U.S. Geological Survey
Invasive Species Compendium from the Centre for Agriculture and Bioscience International (CABI)
EDDMapS Species Information EDDMapS Species Information
Shallow (1-2 (7) meters deep) waters of acidic to alkaline lakes and streams (FNA 2000; DiTomaso and Healy 2003).
Plants decompose quickly and populations often decline in water temperatures above 25 degrees Celsius (DiTomaso and Healy 2003). Periods of pro-longed temperatures near freezing can kill plants (DiTomaso and Healy 2003). It is very susceptible to iron deficiency and grows best under low light (about 100 lux) at temperatures ranging from 10-25 Celsius (DiTomaso and Healy 2003).
Only male plants have been documented to occur outside of its native Brazilian range; therefore, reproduction occurs vegetatively in the U.S. (FNA 2000). Vegetative reproductive structures, such as turions or bulbils, have not been observed (Cook and Urmi-Konig 1984 in FNA 2000). Plant in the U.S. do not usually produce fruits and seeds (DiTomaso and Healy 2003). The fruit capsule is 7-15 mm long and 3-6 mm in diameter at it widest part, thin-walled, and translucent (DiTomaso and Healy 2003). Seeds are elliptical, 5-8 mm long, 2 mm wide, with a 3-4mm beak, and papillate (DiTomaso and Healy 2003).
Reproductive Characteristics (Life Cycle)
At approximate intervals of every 6-12 internodes are specialized leaf nodes called ‘double nodes’(DiTomaso and Healy 2003). The double nodes have a shorter interval and are where adventitious roots and lateral branches can grow. Only fragmented stems that contain a double node can develop into new plants. Reproduction is by stolons and stem fragments (DiTomaso and Healy 2003).
- Additional ReferencesLegend: View Online Publication
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- DiTomaso, J.M. and E.A. Healy. 2003. Aquatic and riparian weeds of the West. Regents of University of California, Division of Agriculture and Natural Resources, Publication 3421.
- Flora of North America Editorial Committee (FNA). 2000. Flora of North America north of Mexico. Vol. 22. Magnoliophyta: Alismatidae, Arecidae, Commelinidae (in part), and Zingiberidae. Oxford Univ. Press, New York. xxiii + 352 pp.
- Montana Department of Agriculture (MDA). 2017. Montana Noxious Weed List. February. Helena, Montana.
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