Quick Facts

Quick facts

• Eurasian Water Milfoil (Myriophyllum spicatum) is an aquatic plant native to Eurasia and parts of Africa that has spread to many other parts of the world as an invasive weed.
• Although present in Australia it has not yet been naturalised.
• It has stems up to 7 m or more long and feathery leaves in rings around the stem.
• It mostly grows totally submerged, except when flowering, when the spike-like inflorescences stand up above water surface.
• It grows quickly in calm water bodies such as reservoirs, ponds and lakes, eventually blocking waterways and impacting on habitats and biodiversity and human activities.
• It is not yet recorded as naturalised in Australia, but if it escapes from aquaria or ponds it could become a serious weed of lakes, dams and reservoirs.

What Does It Look Like?

What is it?

Eurasian Water Milfoil (Myriophyllum spicatum) is a mostly submerged perennial aquatic herb, that is rooted in the substrate. Its stems are hairless, reddish brown to whitish pink, up to 7 m or more long and 5 mm wide, generally branching near the water surface to form a dense canopy and becoming leafless towards the base. Its leaves are robust, all submerged, in rings of three or four around the stem, greyish green or olive-green, 1.5–4 cm long and stiffly feather-like. Each leaf has 14–24 pairs of fine, linear segments, 6–12 mm long.

Male and female flowers are on the same plant. The flower heads form at the tips of the stems, above the water, and are narrow spikes up to 8 cm long with rings of four small flowers. Female flowers are in the lower rings and are about 1 mm long, they lack petals and are greenish in colour. Male flowers are in the upper rings, with four reddish or pink petals, to 2.5 mm long, and eight stamens.

The fruit is egg-shaped, 3 mm long, with four dry, 1-seeded nutlets (Sainty & Jacobs 1981, 2003; Holm et al. 1997; Thorp & Wilson 1998 – ; Waterhouse & Mitchell 1998; Sainty & Associates 2002; Weber 2003; Osmond undated).

For further information and assistance with identification of Eurasian Water Milfoil contact the herbarium in your state or territory.

Flower colour

• Red 
• Green
• Pink

Growth form (weed type/habit)

Aquatic

Where it currently grows? Preferred habitat

Eurasian Water Milfoil grows in lakes, ponds, canals and reservoirs. It tolerates a broad temperature range, wide pH range and brackish water conditions. It can grow in water 0.5 to 10 m deep, but most commonly at depths up to 3 m. Although preferring static or slow-moving water it will also grow in fast-moving water (Osmond undated). Plants can survive stranding or water up to 17 m deep (Holm et al. 1997; Thorp & Wilson 1998 -; Waterhouse & Mitchell 1998; Sainty & Associates 2002; Osmond undated).

Are there similar species?

It is important not to confuse the introduced Eurasian Water Milfoil or Parrot's Feather (Myriophyllum aquaticum) with native Myriophyllum species. While some native species are easily recognised, others belong to complex groups in which mature fruits are usually needed for identification (Sainty & Jacobs 1981, 2003; Orchard 1986; Romanowski 1998; Wilson 2002).

All the leaves of Eurasian Water Milfoil and Parrot's Feather are comb-like or feathery, but the leaves are more finely divided and are all submerged in the former species. Parrot's Feather has distinctive glaucous (blue-green with a whitish bloom) leaves on shoots that emerge above the water surface. Unlike Eurasian Water Milfoil, the plants of Parrot's Feather only have female flowers in Australia (Orchard 1986; EPPO 2008). The native Watermilfoil (Myriophyllum salsugineum) has finely divided submerged leaves similar to those of Eurasian Water Milfoil, but it also has undivided reddish purple emergent leaves (Sainty & Jacobs 2003).

Eurasian Water Milfoil can also be confused with submerged growth of Hornwort (Ceratophyllum demersum), which is a free-floating aquatic. Its leaves are not comb-like or feathery as in Eurasian Water Milfoil or Parrot's Feather, but narrowly branched or forked 2-4 times (Sainty & Jacobs 2003; Auckland Regional Council 2008).

Why Is It A Weed?

What are its impacts?

Native ecosystems: Eurasian Water Milfoil is a serious weed of lakes, water storages, canals and rivers in southern Africa, North America and India. In these locations it chokes water bodies, affecting fish and shellfish production, irrigation (clogging water intakes and flow meters for irrigation and flood control), recreational use (impeding or interfering with activities such as boating, water skiing, fishing and swimming) and boat traffic (Holm et al. 1997; Waterhouse & Mitchell 1998; Sainty & Associates 2002; Jordan 2007; Osmond undated). It forms dense stands that shade out other species, alter the temperature profile of the water body, and decrease the diversity of invertebrates and fish numbers (Thorp & Wilson 1998 -; Sainty & Associates 2002; Weber 2003; Osmond undated). In Australia it is a potential weed posing a serious threat to certain habitats (Waterhouse & Mitchell 1998).

How does it spread?

Eurasian Water Milfoil and other Myriophyllum species have been largely spread by human activity, mainly via the trade in aquatic plants for aquaria and ponds. It spreads vegetatively by stem pieces, and less commonly by seed. It is dispersed by moving water and human activities such as boating, and possibly by water birds (Holm et al. 1997; Thorp & Wilson 1998 -; Waterhouse & Mitchell 1998; Sainty & Associates 2002; Osmond undated).

What is its history in Australia?

Eurasian Water Milfoil was introduced to Australia as an ornamental plant for aquaria and ponds, and is still available through some nurseries. It is not known to be naturalised in Australia (Romanowski 1998; Sainty & Jacobs 2003).

How To Manage It?

Best practice management

Non-chemical control: Mechanical harvesting of Eurasian Water Milfoil can lead to rapid re-infestation due to the plants fragmenting (Osmond undated). Control by environmental modification through water level management (i.e. fluctuations with periodic lowering and raising of water levels) can be used to reduce aquatic weed growth. Excess growth of Eurasian Water Milfoil has been managed overseas with regular changes in water level and use of approved herbicide treatments, but this technique must be used with caution to avoid negative impacts on desirable species and native habitats (Smith 1971; Sainty & Jacobs 1981, 2003).

Chemical control: Eurasian Water Milfoil is susceptible to some herbicides but regrowth is fast. If plants are not killed repeated control will be necessary (Crowell 1999; Weber 2003). Herbicides must be approved for use in aquatic environments.

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)

Eurasian Water Milfoil is a perennial (lives longer than 2 years) that may die back to the base in winter and reshoot in spring. Growth is most prolific in summer. Flowering is most likely to occur in late summer and early autumn (Holm et al. 1997; Thorp & Wilson 1998 -; Sainty & Jacobs 1981, 2003; Sainty & Associates 2002; Osmond undated). Plants mostly spread as vegetative fragments, and during the growing season they will automatically fragment, often developing roots before they separate from the parent plant (Osmond undated).

Where Is It Found?

Which states and territories is it found?

Not naturalised in any Australian states or territories.

What areas within states and territories is it found?

Eurasian Water Milfoil is not known to be naturalised in Australia.

Where does it originate?

Eurasian Water Milfoil is native to Europe, Asia and northern Africa, but is introduced in many other parts of the world, where is it a serious weed of lakes and reservoirs (Holm et al. 1997; Sainty & Associates 2002; Romanowski 1998; Sainty & Jacobs 2003).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

NO

Where is it a declared weed?

NSW, NT, QLD, SA

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 spicatum

Other scientific names (synonyms)?

Myriophyllum exalbescens Fern.

Does it have other known common name(s)?

Eurasian Watermilfoil, Eurasian Water-milfoil, Spiked Water Milfoil