COVE
Waterways Management
Aquatic Weed Identification - The top 10 aquatic weeds in Western Australia.
Leafy Elodea
Leafy elodea (Egeria densa) is a declared pest in Western Australia (WA).
Form: aquatic — perennial
Status: present in WA
Appearance
A submerged, much branched perennial freshwater aquatic herb usually rooted in the bottom mud. Male and female flowers are produced on separate plants. Female plants have not been recorded in Australia; all reproduction is vegetative.
Stems: Green to brown, slender, much branched 3-5m long, 2-2.5mm wide.
Leaves: Attached direct to stem (no stalks), edged with fine forward pointing teeth. Lower leaves opposite, upper leaves in whorls of three to seven, strap-like and tapering to a point; 1.5-3cm long and 3-5mm wide.
Flowers: White formed in the axils of the upper leaves, and carried to the surface on a thread-like stem. Male flowers in groups of two to four.
Fruit: Cylindrical, 7-8mm long, 3mm diameter.
Hydrolcotyl
Hydrocotyl, water pennywort, hydrocotyle, floating marshpennywort, spaghetti weed, grote waternavel (Hydrocotyle ranunculoides) is a declared pest in Western Australia (WA).
Form: herbaceous aquatic — perennial
Status: present in WA
Appearance
Hairless perennial with long stolons that root at the nodes and grow out over the water.
Leaves: Floating, somewhat kidney to heart shaped to 10cm in diameter, lobed around the margin.
Flowers: Inconspicuous, 3mm diameter, five to ten in number on a slender stalk 2cm long. Flowering spring to autumn.
Fruit: Almost circular in outlined but compressed 2-3mm diameter, breaking into segments
Parrot's Feather
Parrot's feather, Brazilian water milfoil (Myriophyllum aquaticum) is a declared pest in Western Australia (WA)
Form: aquatic
Status: present in WA
Appearance
A bright green perennial freshwater herb that grows from the banks or rises up through several metres of water, forming vigorously-growing tangled mats. Reproduction in Australia is only by vegetative means. Recorded from Perth, Busselton and Margaret River.
Stems: Yellow-green and slender, 2-5m long, creeping and rooting at the nodes near the base of the plant.
Leaves: Bright green, feathery in appearance, in groups (whorls) of four to six, becoming more densely crowded towards the top of the stem. Each leaf is linear to elliptical in outline, 3-3.5cm long, deeply divided into 10 to 14 pairs of thread-like segments.
Flowers: Solitary, arising on short stalks between two small bracts about 1.5mm long in the upper leaf axils. Petals are absent, sepals (outermost parts of the flower) four in number, white-translucent and 1-1.5mm long.
Salvinia Molesta
Salvinia (Salvinia molesta) is a declared pest in Western Australia (WA).
Form: aquatic
Status: present in WA
Appearance
Salvinia is a free-floating perennial aquatic fern made up of pairs of oval, green to brown leaves connected by a horizontal stem. The top of each leaf has many tiny, hairlike structures that split then rejoin at the tips to form an eggbeater-like structure. Under the water, each plant produces other leaves that look like a small bunch of brown roots. Salvinia is a Weed of National Significance (WoNS).
It grows quickly to form thick mats covering lakes, slow-moving rivers and other waterways. These mats severely interfere with the use of water bodies for irrigation, flood mitigation and conservation of wildlife. It helps accumulate litter and promotes water stagnation that encourages breeding of mosquitoes.
Stems: Slender jointed and much branched to 30cm long to 1-2mm diameter. Length of leaf nodes varies inversely with density of the plants.
Leaves: Two kinds: a submerged leaf which is brown and deeply divided into a group of unbranched root-like filaments 2-25cm long. Emergent leaves are green, roughly circular, two lobed, with a smooth edge. Upper surface covered in rows of waxy, eggbeater-shaped hairs 1mm long.
Water Hyacinth
Water hyacinth, floating water hyacinth, (Eichhornia crassipes) is a declared pest in Western Australia (WA).
Form: aquatic — perennial
Status: present in WA
Appearance
An erect floating perennial herb, reproducing by stolons and from seed.
Stems: Erect, to 60cm long and bearing flowers; or horizontal (stolons), about 10cm long and producing new plants from terminal buds. Hairless.
Leaves: Two types of leaves - up 60cm long, narrow and standing upright; others have an almost round blade up to 30cm diameter and curved upwards with somewhat wavy edges. Both leaf types are smooth and hairless, glossy and have semi parallel veins. Leaf stalks to 50cm long with bladder like swellings, either bulbous or elongated, which contain air cells that enable the plant to float. Dense packed plants mainly have the narrow leaf form.
Flowers: Very attractive, large lilac, funnel shaped 4-7cm diameter, with six lobes or petals, the upper lobe with a yellow blotch in the centre surrounded by darker purple; produced in spikes about 15cm long on stalks about the same length. Spikes average about eight flowers but the range can be three to 35. Flowers only last a few days then the flower stalks bend to submerge the fruit.
Fruit: A narrow, three celled capsule 1-1.5cm long containing up to 300 seeds.
Seed: Egg shaped 1-1.5mm long with ribs running the length of the seed. Seed can remain viable for up to 20 years.
Water Lettuce
Water lettuce (Pistia stratiotes) is a declared pest in Western Australia (WA).
Form: aquatic
Status: present in WA
Appearance
A free-floating plant widespread throughout the tropics, with a dense rosette of overlapping leaves on a very short stem and long feathery roots. Reproduces vegetatively and by seed.
Stems: To 60cm long, linking the rosettes.
Leaves: Pale yellow-green or grey-green, fan shaped, with six or more prominent veins on the under surface, 2.5-15cm long and to 8cm wide, densely covered with short white hairs which trap air and give the plant the ability to float.
Flowers: Inconspicuous, surrounded by a small leaf-like bract 7-12mm long and 5mm wide that encloses the minute male and female flowers.
Fruit: Fleshy, 5-8mm diameter.
Seed: Each seed is 2mm long. Green at first brown when mature, oblong with a thick wrinkled coat, four to 15 seeds per fruit.
Amazon Frogbit
Amazon Frogbit is an Alien to Western Australia
Form: Aquatic
Status : Present in WA
Appearance
Limnobium laevigatum, or Amazon Frogbit, is 50cm high 1 to 8 cm wide it is a oating plant that is reminiscent of a large duckweed (Lemna minor). It is native to Central and South America and can be found growing wild in lakes, ponds and slow rivers. Since this species is far more tolerant of extreme temperatures, it has become increasingly more common in cultivation.
The growing habits of laevigatum is similar to that of most other oating plants. The oating rosettes send runners out into the water, the ends of which form juvenile plants. A large mat of runners and adult plants can develop very quickly, which in turn can result in the unwelcome shading of plants growing below. The juvenile plants have a great capacity for distribution in that they are small, and they oat, and can be easily and quickly carried along by water currents.
Natives that may need some management
Duck Weed
Duck Weed is a Native in Western Australia (WA)
Form : aquatic Perennial
Appearance
Duckweed is one of the smallest flowering, free-floating plants found around the world. Measuring just 1cm to 3cm in length,with roots trailing down on the bottom side of the plant up to 4cm long. duckweed floats on the water surface in colonies not attached to the bottom. Duckweed floats wherever the wind or currents take it, absorbing nutrients from the leaf undersurface and a very fine root hanging from it.
Duckweed can have one leaf or up to three leaves, known as fronds, about the size of a pencil eraser head, with a single root hair.
Duckweed prefers eutrophic, motionless fresh water in wetlands, ponds, lakes and slow moving streams.
Typha
Typha (Orientals/Domingensis)
Form: aquatic Perennial
Appearance
Broad-leaved Cumbungi is a tall, rigid, perennial, rhizomatous reed to 4.5 m high with flat strap-like leaves to 2 m long and a thick cylindrical stem. The flowering stem is tipped by a cylindric, brown, velvety brush of densely packed tiny flowers. The upper part of the inflorescence has minute male flowers and the lower part equally small female flowers. There is a small gap between the two parts of the inflorescence. It flowers in spring and summer.
Broad-leaved Cumbungi is very similar to and difficult to separate from the Narrow-leaved Cumbungi (Typha domingensis). Both Typha species are now considered native to Western Australia,
Both species are found in swamps and fringing lakes and watercourses, the two sometimes growing together. As well as being very similar, intermediates between the two species have been found.
Azolla
Azolla is Native to WA
Appearance
Red Azolla is a small, native, oating fern – one of only six, free- oating, aquatic fern species. It grows from 1 cm to 2.5 cm wide and is a bright green colour. Its colour changes to deep red when it is exposed to the sun, thus the name Red Azolla.
Azolla grows in waterways in dense patches, which can look like a green or red carpet.
