Myriophyllum tenellum (Slender Water-milfoil)

Plant Info
Also known as: Dwarf Water-milfoil
Family:Haloragaceae (Water-milfoil)
Life cycle:perennial
Habitat:part shade, sun; shallow to 5 feet deep water, sandy soil; soft water lakes, shores
Bloom season:June - August
Plant height:1 to 12 inches
Wetland Indicator Status:GP: OBL MW: OBL NCNE: OBL
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: 4-petals Flower shape: indistinct Cluster type: spike

[photo of flowering stems] Loose, spike-like, erect cluster at the top of the stem, rising above the water's surface, with separate male and female flowers on the same plant (monoecious). Flowers are single in the axils of leaf-like bracts, 4-parted, stalkless, minute.

[close-up of flowers] Male flowers have 4 pale, oblong petals and 4 yellow stamens. Female flowers are petal-less, have a 4-parted ovary each with a feathery style at the tip that is often reddish.

Leaves and stems: Leaf attachment: alternate Leaf type: simple

[photo of leaves] Leaves are alternate, stubby, toothless, rounded at the tip, not much longer than the stem is wide, often shorter.

[photo of stems on the rhizome] Stems are slender, erect, mostly unbranched, white near the base and green above, arising singly at irregular intervals along a long rhizome.

Fruit: Fruit type: seed without plume

[photo of developing fruit] Fruit is brown, about 1 mm long, with 4 lobes and eventually splits into 4 seeds.


Slender Water-milfoil is a common aquatic found in soft water lakes with sandy bottoms in the northeastern quadrant of Minnesota, where it reaches the southwestern edge of its range. Plants are most often submersed with just the flowering spikes rising out of the water, though may become stranded on shores when water recedes. While it can form large colonies, vegetative stands may go unnoticed due to the toothpick-like form of essentially leafless stems. Flowering stems have been known to reach 12 inches tall but vegetative stems are more common and typically less than half that height. Stems are single at irregular intervals along the rhizome and are usually unbranched, only occasionally branched or with multiple spikes. It is not easily confused with any other species and once you do notice it, you seem to find it everywhere.

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More photos

Photos by Peter M. Dziuk taken in Itasca County.


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