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Montana Field Guides

Parrot Feather Water-milfoil - Myriophyllum aquaticum
Other Names:  Parrot's-feather, Myriophyllum brasiliense

Regulated Weed: Priority 3
Non-native Species

Global Rank: GNR
State Rank: SNR
(see State Rank Reason below)

Agency Status
MNPS Threat Rank:

External Links

State Rank Reason (see State Rank above)
Myriophyllum aquaticum is not known to occur in Montana. Myriophyllum brasiliense was reported to occur southeast of Missoula, Montana, but no specimen or specific location has been identified as of 2017 (Lackschewitz 1991). 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.

Native to South America, Myriophyllum aquaticum was intentionally introduced in North America for use in water gardens and aquariums, but has escaped cultivation through intentional plantings and by the spread of plant fragments (Invasive Species Specialist Group (ISSG) 2014). Upon introduction this plant is aggressive, spreads rapidly, and forms dense mats, making eradication very difficult. Preventing deliberate plantings and spread from plant fragments are the best means to keep this plant out of Montana’s waters.
General Description
PLANTS: Aquatic perennials with rhizomes and finely dissected, whorled leaves that are both emergent (above the water) and submergent (below the water) (ISSG 2014). Plants are bright green to glaucous-green (whitish-green). The emergent leaves are stiffer, can grow to 1 foot above the water, and appear almost like miniature fir trees.

LEAVES: Emergent and submergent leaves are pinnately-divided (feather-like) and whorled in groups of 4-6 (ISSG 2014). Emergent leaves range from 1.5-3.5 cm long with 20-30 divisions per leaf. Submergent leaves range from 2-5 cm long with 6-18 divisions per leaf. Submergent leaves may be more reddish, limp, and appear decadent.

INFLORESCENCE: A terminal bracteate spike with whorled, sessile flowers (ISSG 2014). Flowers are inconspicuous, small, and with white petals.

ROOTS: Plant have rhizomes and adventitious roots (ISSG 2014). Adventitious roots grow from leaf nodes.

Diagnostic Characteristics
Montana has at least four species of water-milfoil, and users of this field guide are encouraged to identify specimens using the Manual of Montana Vascular Plants (Lesica 2012). Our native water-milfoil all overwinter as tight balls of unexpanded leaves (turions).

Plants with limp submergent leaves and stiffer, upright emergent leaves that stick above the water’s surface distinguishes Parrot Feather Water-milfoil. In addition, plants are a brighter green or whitish-green when compared to the species below. Reproduction is from rhizomes. Turions, winterbuds, or tubers are lacking.

Shortspike Water-milfoil (Myriophyllum sibiricum) is native to Montana. It also has flowering spikes with bracts less than 4mm, but its whorled leaves have 4 to 14 pairs of segments that mostly spread (Lesica 2014). In addition, the lower segments are longest and gradually shorten towards the leaf tip (Parkinson et al. 2011). Turions are present in the fall and winter.

Whorl-leaf Water-milfoil (Myriophyllum verticillatum) is native to Montana. Its flowering spikes have pinnately divided bracts that are longer than the fruits. Its whorled leaves are up to 45 mm long and have 18 to 34 pairs of segments (Lesica 2012). In addition, the lower segments are longest and more abruptly shorten towards the leaf tip (Parkinson et al. 2011). Turions are present in the fall and winter.

Coon’s-tail or Hornwort (Ceratophyllum demersum) is a native plant that initially may appear similar. However, its leaves are linear-forked segments whorled around the stem; they are not pinnately divided (no central mid-rib) (Parkinson et al. 2011; Lesica 2012). Plants are usually sterile and reproduction is mostly by overwintering turions (Lesica 2012).

Range Comments
Native to the Amazon River in South America and naturalized in many warmer climates (Washington State Department of Ecology 2011). In the U.S. it was first documented in 1890 in the Washington D.C. area (Washington State Department of Ecology 2011). In Washington State a single population was reported in 1944 and an herbarium specimen was documented from Wahkiakum County in 1983 (Washington State Department of Ecology 2011). It is an invasive exotic, occurring in the southern states and colonizing waterways northward, particularly along the coast.

Observations in Montana Natural Heritage Program Database
Number of Observations: 2

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)

Slow-moving waters of freshwater lakes, ponds, streams, and ditches (ISSG 2014). It appears well adapted to high-nutrient environments (Washington State Department of Ecology 2011). It grows best in shallow water, but can occur as floating plants in deep, high-nutrient enriched lakes. Emergent stems can survive on wet river banks and lake shores, withstanding moderate water-level fluctuations.

Myriophyllum aquaticum forms dense mats that can entirely cover the water in shallow lakes and restrict water flow in drainage ditches (Washington State Department of Ecology 2011). This type of growth changes the physical and chemical characteristics of lakes and streams. It provides good habitat for mosquito larvae (Washington State Department of Ecology 2011). It can shade out algae which are the basis of the aquatic food chain (Washington State Department of Ecology 2011).

Reproductive Characteristics
Life Cycle [Adapted from Washington State Department of Ecology 2011.]

As water temperatures warm in the spring, shoots grow quickly from overwintering rhizomes (which are underground stems). Adventitious roots grow from rhizomes. Rhizomes also provide buoyancy for the growth of emergent stems in summer. Flowering occurs mostly in the spring, but may also occur in fall. Flowers grow from emergent leaf nodes, but have no stalk (are sessile). Male plants have not been found outside of South America. All U.S. populations appear to be colonized by female plants, but with no ability to be fertilized seeds are not produced. Plants also lack tubers, turions, winterbuds, or the ability to autofragment (purposely fragment). Therefore, all reproduction is by rhizomes and stem fragments. Disturbance of plants can result in fragments that will spread in the water column and root in the substrate. Rhizomes the are kept cold and moist can survive in a refrigerator for one year.

Myriophyllum aquaticum forms dense mats that can entirely cover the water in shallow lakes. The tough stems make it difficult to boat, swim, fish, or water ski. Upon introduction this plant is aggressive in spreading rapidly and densely, making eradication very difficult. It has been estimated that the diking district staff in southwestern Washington spends $30,000-$40,000 per year to mechanically control it in the Longview/Kelso drainage ditches where it is well established. The sections below are adapted from Washington State Department of Ecology 2011.

Preventing deliberate plantings and spread from plant fragments are the best means to keep this plant out of Montana’s waters.

* Do not dispose aquarium water or plants into water bodies.
* Learn to identify Parrot Feather Water-milfoil and report findings to the Montana Department of Agriculture; Montana Fish, Wildlife and Parks; County Extension agent; or Weed Coordinator.

Herbicide control can be difficult. The emergent leaves have a thick waxy-coating which inhibits herbicide uptake, and requires a wetting agent to penetrate the cuticle. However, the weight of the spray can cause emergent stems to collapse into the water causing the herbicide to wash off before it has penetrated the plant.

Native water-milfoil are susceptible to these herbicides. The herbicide concentration, exposure time before dissipating, timing of chemical control, and other factors are critical to effectively hinder Parrot Feather Water-milfoil and reduce impacts to native vegetation. Always follow chemical label instructions and use restrictions. The following herbicides must be applied by applicators with an Aquatic Pest Control license. Consult your County Extension Agent and/or Weed District for more information on herbicidal control and to find out what chemicals are permitted for use in Montana.

* Diquat, 2,4-D, Diquat and complexed copper, Endothall Dipotassium salt, and Endothall and Complexed Coper have been used with excellent results to control Parrot Feather Water-milfoil plants in Washington State.

* Fair control has occurred with Glyphosate. Glyphosate may cause the emergent stems to turn black, but within two weeks plants in Washington recovered. The Monsanto Company has reported that a 1.75% solution with the aquatic version of Rodeo and a surfactant applied to plants in the summer or fall when water levels are low may control plants by 95%.

* A low-volatility ester of 2,4-D at 4.4 to 8l.9 kg/ha sprayed onto the young, actively growing emergent foliage may control plants. The granular formulation of 2,4-D is needed when controlling plants for longer than 12 months.

* In Washington a fall application of Triclopyr on Parrot Feather Water-milfoil was ineffective.

Mechanical control can fragment plants which can escape in the water and start new colonies.
Therefore, cutting, harvesting, and underwater rototilling should not be used unless all available niches in the system have been filled by Parrot Feather Water-milfoil.

Plants can be harvested, but rhizomes are heavy and tough. In Washington certain populations are annually controlled with a dragline. A truck-mounted crane with a special attachment pulls plants out of the ditch. The operation is conducted from August to December of each year in order to manage control.

The rhizomes are robust. In California rhizomes survived over winter when water levels have been drawn down.

Parrot Feather Water-milfoil has a high tannin content which makes it unpalatable to many species of grazers. Biological control agents are currently not available, but many potential agents are or have been studied:

Lysathia flavipes (Boheman): A flea beetle found on plants in Argentina, has caused moderate damage under field conditions.
Lysathia ludoviciana (Fall.): A flea beetle native to the southern U.S. and Caribbean, has used this plant in the laboratory as a host plant for its larvae.
Listronatus marginicollis (Hustache): A weevil found in Argentina that appears to feed on Parrot Feather Water-milfoil.
Argyrotaenia ivana (Fernald), Choristoneura parallela (Robison), and Parapoynx allionealis (Walker): Have been investigated as potential agents.
Pythium carolinianum (Matt.): A fungus investigated as a potential agent.

Contact information for local county Weed District Coordinators can be found on the Montana Weed Control Association Contacts Webpage.

Useful Links:
Montana Biological Weed Control Coordination Project
Montana Department of Agriculture - Noxious Weeds
Montana Weed Control Association
Montana Fish, Wildlife, and Parks - Noxious Weeds
Montana State University Integrated Pest Management Extension
Integrated Noxious Weed Management after Wildfires

  • Additional ReferencesLegend:   View Online Publication
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    • Invasive Species Specialist Group (ISSG). 2004. Ecology of Myriophyllum aquaticum (aquatic plant). ISSG Database, October 14th. Obtained on November 14, 2014.
    • Montana Department of Agriculture (MDA). 2017. Montana Noxious Weed List. February. Helena, Montana.
    • Washington State Department of Ecology. 2011. Non-native invasive freshwater plants: Parrotfeather (Myriophyllum aquaticum), Technical Information. Olympia, Washington. Obtained on November 14, 2014.
    • Washington State Department of Ecology. 2011. Non-native invasive freshwater plants: Parrotfeather (Myriophyllum aquaticum), Technical Information. Olympia, Washington. Obtained on November 14, 2014.
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Parrot Feather Water-milfoil — Myriophyllum aquaticum.  Montana Field Guide.  .  Retrieved on , from