Quick Facts

Quick facts

• Parrot's Feather (Myriophyllum aquaticum) is a freshwater aquatic herb with feathery, blue-green leaves in rings on stems up to 2 m long, forming vigorously growing tangled mats.
• It is widely naturalised in the coastal districts of southern and eastern Australia.
• It is locally troublesome as a weed of ponds, dams, drainage ditches and waterways that impedes water flow, alters habitats, and disrupts recreation and other activities on waterways.
• Seed is not produced in Australia and it spreads vegetatively by broken stem fragments.
• Plants are capable of forming dense mats (especially in nutrient-enriched waters).
• Ornamental use in ponds and aquaria should be discouraged.

What Does It Look Like?

What is it?

Parrot's Feather (Myriophyllum aquaticum) is a stout, blue-green (or sometimes bright to dull light green) aquatic or semi-aquatic perennial herb. Its stems are spreading, creeping or upright, growing up to 2 m long, 4–5 mm in diameter, hairless, and rooting freely at the lower nodes (the joint of a stem from which a leaf arises). The plants form vigorous mats or masses of tangled, leafy stems. The leaves are all arranged in rings around the stem, and those submerged in water are larger than those above water. Submerged leaves are in rings of four to six, to 4 cm long, usually 8–12 mm wide, and much-divided, giving a feathery appearance. The lower leaves usually decay rapidly, leaving long, bare, often yellowish, submerged stems. Above-water leaves are also feathery and are crowded towards the tips of the stems, usually in rings of five or six; they are more spreading on the lower part of stems. They are usually 2.5–3.5 cm long and 7–8 mm wide.

Parrot's Feather usually has male and female flowers on separate plants. There is no known population in Australia with male flowers. Its flowers are small, in the forks of the upper emergent leaves. Female flowers have four sepals that are white-translucent and 1–1.5 mm long. They have no petals.

Fruits are not known in Australian populations (Orchard 1986, 1990; Parsons & Cuthbertson 2001).

For further information and assistance with identification of Parrot's Feather contact the herbarium in your state or territory.

Flower colour

White

Growth form (weed type/habit)

Aquatic

Where it currently grows? Preferred habitat

Parrot's Feather is a plant of slow-moving to static waters, rooting in the shallows, with stems floating out over deeper water to form dense tangled rafts on the surface. It grows in water up to 2 m deep, rooting in mud or gravel, and often extending onto the adjacent saturated banks. It can persist on saturated substrates when water levels drop. It is tolerant of a wide temperature range (thriving in water between 8 ^°C and 30 ^°C) and grows best in water containing high levels of nitrogen. Parrot's Feather grows principally in warm-temperate and subtropical, mainly coastal regions; especially near urban areas (Aston 1973; Orchard 1986, 1990; Romanowski 1998; Parsons & Cuthbertson 2001; Sainty & Jacobs 2004; EPPO 2008).

Are there similar species?

It is important not to confuse the introduced Parrot's Feather with native Water Milfoils (various Myriophyllum species). Parrot's Feather has no close relatives amongst the native Australian Myriophyllum species, and the trained eye should not confuse them, as Parrot's Feather has very distinctive, large, glaucous (blue-green with a whitish bloom) leaves that are feather-like and arranged in rings around the stem. They can stand up to 30 cm or more high in shallow waters or muddy areas. Native Water Milfoils have emergent (occurring above water) leaves that are toothed (serrated), not feather like, with feathery foliage that only occurs below the water surface (unlike Parrot's Feather where it persists above the surface).Only female flowers are produced in Australian plants of Parrot's Feather (Aston 1973; Sainty & Jacobs 1981, 2003; Orchard 1986, 1990; Jeanes 1996; Romanowski 1998; Wilson 2002).

Why Is It A Weed?

What are its impacts?

Parrot's Feather forms dense stands that impede water flow, blocking small creeks, drains and channels. Infestations have negative impacts on the environment, biodiversity, native flora and fauna, transport, recreation, and tourism (Orchard 1986; Thorp & Wilson 1998 -; Sainty & Associates 2004; Richardson et al. 2006).

Agriculture: Aquatic weeds such as Parrot's Feather have detrimental economic impacts related to interference with the flow of irrigation water, hydroelectric power production (floating mats can block intakes, pumps and metering devices), transport, fisheries, recreation, and increased health hazards. It can invade rice fields, affecting crop yield (Parsons & Cuthbertson 2001).

Native ecosystems: While Parrot's Feather may provide cover for some aquatic organisms, it can seriously change physical (e.g. reducing light) and chemical characteristics of water bodies. Infestations alter aquatic ecosystems by shading out algae that are the basis of the aquatic food chain. Dense stands displace and exclude native water plant species, reducing the natural biological diversity, as has been observed in nutrient-enriched coastal or brackish water conditions (Weber 2003; EPPO 2008).

How does it spread?

The reproduction of Parrot's Feather is entirely vegetative in Australia. The stems are brittle and plants spread by fragmentation of the floating mats by wave action, boats, mechanical harvesting and other activities. Stem fragments move in stream flows and regenerate by rooting wherever they settle on sediments (Orchard 1986, 1990; Parsons & Cuthbertson 2001; EPPO 2008). Parrot's Feather has been widely used as an ornamental plant in aquaria and garden ponds, so nursery and personal trading of plants pose further risks of it being spread by humans from the dumping of aquarium contents in waterways. This has been a major cause of long distance spread of the plant (Parsons & Cuthbertson 2001).

What is its history in Australia?

Parrot's Feather was introduced to Australia as an ornamental plant for aquaria and ponds. Only female plants have been introduced or recorded, so it does not produce fertile seed here. Parrot's Feather was first recorded as naturalised in Sydney in 1908 and has since spread and become invasive in other parts of Australia (Romanowski 1998; Parsons & Cuthbertson 2001; Gunasekera et al. 2002).

How To Manage It?

Best practice management

Prevention: Preventing the introduction and spread of Parrot's Feather is the best means of weed control. Care should be taken to prevent further imports into Australia because, if male plants become established, seeds could be produced and increase the risk of spread (Sainty & Jacobs 2003).

Non-chemical control: Manual control: Physical control by mechanical cutting is usually not effective because plants rapidly regrow from fragmented stems, however biomass harvesting may be possible. Hand pulling, subsurface cutting, and use of draglines may give useful temporary control, but it is essential to minimise the movement of stem fragments. Any material removed must be disposed of carefully. In small dams it has been successfully controlled by covering the water with black plastic sheeting for several weeks (Parsons & Cuthbertson 2001; Weber 2003; EPPO 2008).

Chemical control: In general, herbicides give effective control in most situations. Herbicides must be approved for use in aquatic environments (Kleinschmidt & Johnson 1977; Parsons & Cuthbertson 2001; Peirce & Pratt 2002; Weber 2003; EPPO 2008).

See the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au 

Does it have a biological control agent?

NO

When does it grow? (lifecycle/growth calendar)

Parrot's Feather is a perennial (lives for longer than 2 years) herb. Flowering mainly occurs in November-December, but in warm coastal situations it flowers through most of the year. No male plants are known in Australia and seed is not produced here (Orchard 1986; Parsons & Cuthbertson 2001; Sainty & Associates 2004). Reproduction occurs vegetatively, with stem fragments producing roots, and new stems developing from buds when these fragments come to rest. New plants grow most vigorously during summer and less so during winter, but rapid growth recommences in spring with new stems extending the colony. High nutrient levels promote dense growths (Sainty & Jacobs 1981; Parsons & Cuthbertson 2001).

Where Is It Found?

Which states and territories is it found?

NSW, QLD, SA, TAS, VIC, WA

What areas within states and territories is it found?

Parrot's Feather infestations occur in a number of Australian locations, mainly on the coastal plains, from south-eastern Queensland to near Melbourne, but also extending to the south-western Slopes in New South Wales and into northern Victoria. A small number of infestations occur in Tasmania, South Australia and Western Australia (Orchard 1986; Parsons & Cuthbertson 2001; Barker et al. 2005; Tasmanian Department of Primary Industries and Water 2008).

Where does it originate?

Parrot's Feather is native to the lowlands of central South America, but has been introduced throughout tropical and warm temperate regions of the world, partly as an escape from the aquarium trade (Orchard 1986, Parsons & Cuthbertson 2001).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

NO

Where is it a declared weed?

ACT, TAS, WA

Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?

NO

Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?

NO

Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Myriophyllum aquaticum

Other scientific names (synonyms)?

• Enydria aquatica Vell.
• Myriophyllum brasiliense Cambess

Does it have other known common name(s)?

Brazilian Water Milfoil, Brazilian Water-milfoil, Parrotfeather, Thread-of-life, Thread of Life