Eurasian water-milfoil

Myriophyllum spicatum
Aquatic
Whorled
Fern-like
Red
Green

Eurasian water milfoil is a submerged perennial plant. Stems are rooted at the base and grow towards the surface. It can grow in water from 0.5 to 10 m deep, but most commonly at depths up to 3 m deep and has feather like foliage.

Eurasian water milfoil is a prohibited invasive plant under the Biosecurity Act 2014.

Common names 
Also known as: spike water-milfoil,
Family 
Haloragaceae
Deciduous 
No
Flowering time 
Unknown in Australia
Native/Exotic 
Exotic
Origin 
Eurasian water milfoil is native to Europe, Asia and northern Africa.
Notifiable 
Yes
State declaration 
Category 1
Council declaration 
As per State Declaration
Known distribution 

Not found in Queensland but has the potential, if introduced, to become a pest in most parts of Queensland. Is proving a major pest in the Great Lakes USA and Canada.

Habitat 

It can tolerate and thrive in a range of temperatures and water conditions, including low levels of salinity. Grows quickly in calm water bodies such as reservoirs and dams.

Habit 

A perennial, dicot herb with long branching stems and feather-like whorled leaves that is submersed and rooted to the substrate.

Myriophyllum spicatum grows into dense infestations which shades out and replaces other aquatic plants and is of less value as a food resource than the native plants it replaces. At high densities, it supports fewer aquatic insects which serve as a food resource for fish. Large predatory fish lose foraging space and are less efficient at obtaining prey. Another impact is a reduction in oxygen levels within the water due to the decay of the large mats of the plant. The dense mats impede water movement and interfere with recreational activities such as swimming, boating, fishing and water skiing.

Stem and leaves 

A perennial, dicot herb with long branching stems and feather-like whorled leaves that is submersed and rooted to the substrate, Stems are slender, smooth, 2- 6m long, reddish-brown to whitish-pink, and branch several times near the water surface. Leaves are olive-green, < 5cm. Long, soft, deeply divided, and feather-like. Each leaf has a central axis (midrib) with 14-24 filiform segments on each side. Leaf whorls arranged along the stems in whorls of 3 to 6 (usually 4) leaves. Whorl nodes approx. < a centimetre apart. Fibrous roots that can develop on fragments of plants.

Flowers and fruits 

 Has small reddish flowers found above the water on a spike. Flower spike approx. 20cm long and held above the water with reddish flowers arranged in 4-flowered whorls along spike. Four petals, approx. 3mm long, 4 sepals, and 8 stamens. Four lobed fruit that splits into 4 nutlets. 

Reproduction and dispersal 

Myriophyllum spicatum can spread by sexual or vegetative reproduction with the majority of local reproduction by stolons and vegetative fragments. Eurasian water milfoil spreads mostly via plant fragments. During the growing season plants automatically fragment, often developing roots before they separate from the parent plant. Water movement and human activities may also cause fragmentation. Fragments are spread over long distances by water currents and are mainly dispersed between water bodies by boating and fishing activities.Average seed set of 112 seeds per stalk.

Similar species 

Native myriophyllum ssp., ceratophyllum demersum