This submerged aquatic plant is a perennial that develops stems up to
9' long. The stems branch sparingly below and abundantly above; the
upper stems often extend parallel to the surface of the water.
Individual stems are light green, pale red, pale reddish green, or
nearly white; they are terete, slightly succulent, and glabrous. Along
these stems, there are whorls of 4 leaves (rarely 3 or 5) that are
medium to dark green and glabrous. The internodes (spatial separation
along the stem) of the whorled leaves are about ¾-2" in length.
Individual leaves are ¾-1½" long and a little less across; they are
deeply pinnatifid, each leaf dividing into 10-20 filiform (worm-like)
lobes on each side. This provides the leaves with a feathery
The upper stems terminate in floral spikes about 2-8" long.
These spikes are usually exerted above the water surface. The central
stalks of these spikes resemble the stems, except they are slightly
more narrow. Each spike produces sessile unisexual flowers (rarely
perfect) that are arranged in whorls of 4; the male flowers are located
above, while the female flowers are located below. These whorled
flowers are widely separated from each other along each spike. Each
male flower is about 3 mm. long, consisting of 4 pink petals
and 8 stamens; the petals are early-deciduous.
Each female flower is about 2-3 mm. long, consisting of a 4-lobed
pistil with feathery stigmata; petals are insignificant or
absent. Underneath each male flower, there is a green bractlet that is
oblong-lanceolate or oblanceolate in shape. Underneath each female
flower, there is a green bractlet that is oval in shape. These
bractlets are about the same length or a little shorter than the
blooming period usually occurs from early summer to early fall. If the
weather and water are warm, individual plants may bloom more than one
time per year. The flowers are cross-pollinated by wind.
the floral spikes start to sag into the water as the fruits of the
female flowers develop. Each fruit is 2 mm. long and globoid-ovoid in
with 4 lateral lobes; these lobes are smooth, except along their
margins, where they may be slightly warty. Each fruit divides into 4
chunky 3-sided seeds. The root system is shallow and fibrous. This
plant can reproduce vegetatively as its fragile stems often divide,
forming plant fragments that drift in the water. If the stems of these
plant fragments become lodged in the substrate of the water body, they
can develop new roots. Winter turions (dense buds of cold-adapted
leaves) are not developed; instead this plant dies down to its root
crown for the winter.
The preference is full sun,
clear alkaline water up to 8' deep, and a substrate containing clay or
other fine inorganic material. However, Eurasia Water Milfoil will
adapt to more acidic water and substrates containing sand, silt, or
gravel. This plant can spread aggressively and it should not be planted
in North America.
The non-native Eurasian
Water Milfoil is occasional in northern and central Illinois, while in
the southern section of the state it is uncommon. However, this
invasive plant is still expanding its range in Illinois and it will
undoubtedly become more common in the future. Distribution records from
herbariums probably underestimate its abundance within the state.
Eurasian Water Milfoil was introduced into North America from Eurasia;
it also occurs in parts of Africa. The earliest records of this plant
in Illinois are dated 1916, when it was found in Lake County. Habitats
include lakes, ponds, reservoirs, drainage canals, and streams with
slow currents. By displacing native aquatic plants, Eurasian Water
Milfoil can become the dominant aquatic plant in a body of water.
Generally, young human-created bodies of water are preferred habitats
as there is little build-up of organic matter to acidify the water and
there is little shade from neighboring trees and shrubs.
One possible biocontrol agent is the Water
This weevil is native to the American Midwest
and it is known to feed on Eurasian Water Milfoil. However, it will
also feed on native water milfoil species (Myriophyllum
). Pond Snails (Lymnaea
Wheel Snails (Planorbis
also feed on these plants. Some vertebrate animals feed
milfoil species. According to Pearse (1918), 2-5% of the food of
three fishes consisted of water milfoil in Wisconsin; these fish
species are Lepomis
(Pumpkinseed), Noturus gyrinus
Cat), and Perca
(Yellow Perch). Several turtles also feed on
these aquatic plants, including Chelydra
(Painted Turtle), Emys
and Trachemys scripta
(Slider); see Lagler (1943) and Ernst et al.
(1994). Several wetland birds eat the foliage and/or seeds of water
milfoil. They include such species as Cygnus buccinator
Swan), Anas discors
(Blue-Winged Teal), Anas
(Ruddy Duck), Limnodromus griseus
(Pectoral Sandpiper), and Calidris
Sandpiper); see Martin et al. (1951/1961) and Havera (1999).
The foliage is a minor source of food for muskrats (Hamerstrom
& Blake, 1939). Eurasian Water Milfoil can be spread through
human-related activities. This aquatic plant can cling to boat hulls,
propellers, anchors, boat trailers, and fish nets, from which it can
escape into previously unoccupied lakes and rivers. Because this plant
is sometimes cultivated in aquariums, it can spread into waterways when
the contents of aquariums are dumped by their owners.
The plant fragments were collected from a pond
Champaign, Illinois, but they were photographed indoors.
This is one of the most invasive aquatic plants in the American
Midwest. It closely resembles a native species, Myriophyllum sibiricum
(Northern Water Milfoil), but this latter species has fewer filiform
lobes along the sides of its leaves (about 5-9 lobes for each side).
When Northern Water Milfoil is taken out of the water, its leaves are
less prone to collapse than those of Eurasian Water Milfoil. Both of
these species can be distinguished from other water milfoil species
by the small size of their floral bracts, which are usually
no longer than their flowers (3 mm. in length or less).