Parrot's feather (Myriophyllum aquaticum)

Assessment ID: 1184
Jurisdiction: North Territory
Methodology: Northern Territory Weed Risk Management System - aquatic
Management area: All of NT

Notes: Technical report available at: https://environment.nt.gov.au/media/docs/rangelands/weed-management-publications/wra-report-parrots-feather-updated-logo.pdf

Status: PUBLISHED
Last updated: 26/8/2025 12:58:43 pm AEST

Questions answered: 24 / 46

Weed Risk: 289.16 (Very high)
   Invasiveness (raw/adjusted): 9.00 / 7.497
   Impacts (raw/adjusted): 11.00 / 5.786
   Potential distribution (raw/adjusted): 6.00 / 6.666

Feasibility of Control: 0.00 (Low)
   Control costs (raw/adjusted): 0.00 / 0.000
   Current distribution (raw/adjusted): 0.00 / 0.000
   Persistence (raw/adjusted): 0.00 / 0.000

Result: Targeted control (including biocontrol), protect priority sites

Invasiveness

A1. What is the ability of the plant to establish amongst intact native environments?
Answer: Very High

Comments: 
Myriopyllum aquaticum is a highly competitive plant that is capable of rapid growth and spread (Massachusetts Department of Conservation and Recreation 2003).

It can form dense mats and compete with native aquatic plants, especially in shallow ponds (Texas Invasive Pest and Plant Council 2007).

Forms dense stands that impede flow, especially in nutrient rich water. If male plants are introduced may become a more problem (CRC for Australian Weed Management 2009).

It is able to grow as a terrestrial plant when ponds dry out and has even been found growing on the dry bank of a council tip in Cornwall, UK (Centre for Ecology and Hydrology 2004).

Infestations can alter aquatic ecosystems by shading out the algae in the water column that serve as the basis of the aquatic food web (Washington State Department of Ecology 2009).

Populations of parrot feather may become quite dense and completely colonize small ponds and sloughs and impede water flow in drainage ditches and irrigation canals. It may also compete and replace native species that are of more value to fish and wildlife (Indiana State Department of Natural Resources 2008).

A2. What is the reproductive ability of the plant?

(a) Time to seeding
Answer: >3 yrs/never

Comments: 
Male flowers are not recorded from Australia, so no seeds are produced in Australian populations (Parsons & Cuthbertson 1992).

(b) Annual production of viable seed /m2 or /plant
Answer: None

Comments: 
No specific information available on its seed production.

Male flowers are not recorded from Australia, so no seeds are produced in Australian populations (Parsons and Cuthbertson 1992).

(c) Vegetative reproduction
Answer: Frequent

Comments: 
Reproduction in Australia is wholly by vegetative means. Stem fragments, broken off by water wave action, boats or mechanical harvesting, move readily in stream flow and regenerate wherever the settle on sediments (Parsons and Cuthbertson 1992).

Spreads vegetatively from whole plants or fragments (Texas Invasive Pest and Plant Council 2007).

A3. Do propagules of the plant have properties that allow them to be dispersed long-distance by natural means?

(a) Flying animals (birds, bats)
Answer: Yes

Comments: 
Fragments may break off and attach to crocodiles and other aquatic animals (NT Weed Risk Management Committee 2009).

Like other aquatic plants propagules dispersal, M. aquaticum is also known to be dispersed by water birds (Kelly & Maguire 2009).

Fragments may drift or attach to boats and wildlife and create new infestations elsewhere (Massachusetts Department of Conservation and Recreation 2003).

(b) Other wild animals
Answer: Yes

Comments: 
Fragments may break off and attach to crocodiles and other aquatic animals (NT Weed Risk Management Committee 2009).

(c) Water
Answer: Yes

Comments: 
The stems are fragile and readily break during storm; small fragments can travel long distance in stream flow (Parsons and Cuthbertson 1992).

(d) Wind
Answer: No

Comments: 
No specific information available.

A4. How likely is long-distance dispersal by human-assisted means?

(a) Deliberate spread by people
Answer: Occasional

Comments: 
Myriophyllum aquaticum has been introduced worldwide for use in indoor and outdoor aquaria. It is also a popular garden plant. However, it has escaped cultivation and spread via plant fragments and intentional plantings (Washington State Department of Ecology 2009).

(b) Accidentally by people and vehicles
Answer: Common

Comments: 
Boats would be the most likely vector of dispersal in the Northern Territory (NT Weed Risk Management Committee 2009).

Major long distance dispersal of the plant, however, is mainly the result of people dumping aquarium plants in waterways (Parsons and Cuthbertson 1992).

It is known to be dispersed by or through human mediated vectors such as gardening, the horticulture trade, recreational and industrial boats, clothing and equipment (Kelly & Maguire 2009).

(c) Contaminated produce
Answer: Unlikely

Comments: 
Unlikely (NT Weed Risk Management Committee 2009).

(d) Domestic/farm animals
Answer: Occasional

Comments: 
Buffalo are a possible vector (NT Weed Risk Management Committee 2009).

Impacts

B1. What is the plant's competitive potential?
Answer: High

Comments: 
Myriophyllum aquaticum is a very aggressive plant that is capable of rapid growth and spread which can displace native species and biodiversity (Kelly & Maguire 2009).

Once established, it can form dense mats on the water surface that may restrict light to the complete exclusion of other native plants (Massachusetts Department of Conservation and Recreation 2003).

It has high tannin content, so most grazers, including grass carp, find it unpalatable (Indiana State Department of Natural Resources 2008).

Due to its wide range of habitat preferences it has the ability to compete with submerged, emergent and floating leaved plants (Indiana State Department of Natural Resources 2008).

B2. What is the plant’s potential to modify the existing fire behaviour and alter the fire regime?
Answer: No potential

Comments: 
Aquatic species would not have the potential to alter the fire regime (No reference).

B3. What is the plant’s potential to restrict the physical movement of people, animals, vehicles, machinery and/or water?
Answer: Medium

Comments: 
Populations may be quite dense, sometimes as floating mats that have been uprooted, often choking waterways and impeding navigation (Global Invasive Species Datsbase 2005).

The dense mats formed can hamper fishing, boating, swimming and other activities and the loss of recreational and aesthetic value (Massachusetts Department of Conservation and Recreation 2003).

B4. What is the plant’s potential to negatively affect the health of animals and/or people?
Answer: Low

Comments: 
Parrots feather provides mosquito larvae a refuge from predation, which creates a human health hazard (Sytsma & Anderson 1993).

Can cause drowning. This would be largely restricted to warmer months (Victorian Department of Primary Industries 2009).

B5. Does the plant potentially have negative effects on natural and cultural values?

(a) Reducing habitat quality for native animals?
Answer: High

Comments: 
Myriophyllum aquaticum forms monoculture that often does not provide ideal habitat or food for native wildlife and may limit access to the water for some species. These native wildlife populations may be forced to relocate or perish, ultimately resulting in a loss of biodiversity and a disruptions in the balance of the ecosystems (Kelly & Maguire 2009).

(b) Threatened species or communities
Answer: More than one

Comments: 
The vulnerable Lorentz grunter (Pingalla lorentzi) (Finniss River) is potentially threatened by this species (D. Liddle, NT Biodiversity Conservation, pers. comm. 2009, Woinarski 2006).

The vulnerable Angalarri grunter (Sortum neili) (Victoria River District) is potentially threatened by this species (D. Liddle, NT Biodiversity Conservation, pers. comm. 2009, Stirrat et al 2006).

(c) Sites of natural or cultural significance
Answer: More than one

Comments: 
Significant areas that might be impacted by this species include the Mary River catchment and Kakadu National Park. These are listed as Alligator Rivers coastal floodplains and Mary River coastal floodplains in Harrison et al. (2009) (NT Weed Risk Management Committee 2009).

Free floating mats can interfere with infrastructure, irrigation works, hydro-electric outputs and water supplies (Parsons and Cuthbertson 1992).

It limits the recreational value of infested waters (Parsons and Cuthbertson 1992).

Thick mats can prevent fishing, boating, swimming and other activities in a ponds and lakes (Kelly & Maguire 2009)

B6. Is the plant presumed to have negative effects on environmental health?

(a) Soil chemistry/stability
Answer: No

Comments: 
Not believed to have any impacts on soil chemistry or stability (NT Weed Risk Management Committee 2009).

(b) Water quality
Answer: Yes

Comments: 
It has high tannin content, so most grazers, including grass carp, find it unpalatable (Indiana State Department of Natural Resources 2008).

While parrots feather may provide cover for some aquatic organisms, it can seriously change the physical and chemical characteristics of lakes and streams (Indiana State Department of Natural Resources 2008).

Dense floating mats decrease the air exchange between the water surfaces and the atmosphere. Therefore has potential to alter temperature and dissolved oxygen (Kelly & Maguire 2009).

(c) Hydrology
Answer: Yes

Comments: 
The plant can form free floating mats, be attached and submerged or emergent and is reported to severely impeded water flow (Parsons and Cuthbertson 1992).

Potential distribution

C2. How many broad habitat types in the NT will the plant potentially naturalise in (up to 5)?
Answer: Two

Comments: 
The broad vegetation types in the Northern Territory that Myriophyllum aquaticum will potentially naturalise in are:
  * tropical wetlands
  * permanent waterbodies

Of these, the favoured vegetation type is permanent waterbodies (NT Weed Risk Management Committee 2009, Rossiter-Rachor et al. 2012).

C3. What is the potential of the plant to occur throughout its favoured habitat in the NT (as identified in question 2)?
Answer: Most

Comments: 
Myriophyllum aquaticum has the potential to occur through most of its favoured habitat (NT Weed Risk Management Committee 2009).

Control costs

A1. How detectable is the weed?

(a) Distinguishing features

(b) Active growth period

(c) Height at maturity

A2. What is the general accessibility of infestations at the optimum treatment time?

A3. How expensive is control of the weed in the first year of targeted control, for an infestation that has reached maximum weed density?

(a) Chemical costs

(b) Labour cost

(c) Equipment cost

A4. What is the general community perception of this weed within the region?

Current distribution

B1. What is the current pattern of the species’ distribution across the weed management region?

Persistence

C1. How long will it take to reach the maintenance period?

C2. What is the minimum time period for reproduction of sexual or vegetative propagules?

C3. What is the maximum longevity of sexual or vegetative propagules?

C4. What is the threat of reinfestation from outside the management region?

(a) Long-distance (>100m) dispersal by natural means

(b) Long-distance (>100m) dispersal by human means

References

Centre for Ecology and Hydrology (2004), Information Sheet: Myriophyllum aquaticum (Parrots feather), viewed 21/08/2009, <http://www.nerc-wallingford.ac.uk/research/capm/pdf%20files/24%20Myriophyllum%20aquaticul.pdf>. CRC for Australian Weed Management (2009), Parrots feather - Myriophllum aquaticum, Australian Weeds Committee, viewed 21/08/2009, <http://www.weeds.org.au/cgi-bin/weedident.cgi?tpl=plant.tpl&ibra=all&card=W18>. Global Invasive Species Database (2005), Myriophyllum aquaticum, viewed 26/08/2009,<http://www.issg.org/database/species/ecology.asp?si=401&fr=1&sts=sss&lang=EN>. Harrison, L, McGuire, L, Ward, S, Fisher, A, Pavey, C, Fegan, M & Lynch, B (2009) An inventory of sites of international and national significance for biodiversity values in the Northern Territory, Department of Natural Resources, Environment, The Arts and Sport, Darwin, NT, viewed 17/08/2011, <http://www.nt.gov.au/nreta/environment/conservation/reports.html>. Indiana State Department of Natural Resources (2008), Risk Assessment for Parrotfeather (Myriophyllum aquaticum), viewed 21/08/2009, <http://www.state.in.us/dnr/fishwild/files/fw-Risk_Assessment_Parrotfeather_Aug_2008.pdf>. Kelly, J & Maguire, CM (2009), Parrots feather (Myriophyllum aquaticum) Invasive Species Action Plan, prepared for NIEA and NPWS for Invasive Species Ireland, viewed 26/08/2009, <www.invasivespeciesireland.com>. Massachusetts Department of Conservation and Recreation (2003), Potential Invader: Parrot feather - An exotic aquatic plant, viewed 21/08/2009, <http:/mass.gov/lakesandponds>. Parsons, WT & Cuthbertson, EG (2001), Noxious Weeds of Australia, 2nd edn, CSIRO Publishing, Melbourne, pp. 125-9. More References available at: https://environment.nt.gov.au/media/docs/rangelands/weed-management-publications/wra-report-parrots-feather-updated-logo.pdf