Submersed Plants

Species: Myriophyllum verticillatum L., whorled milfoil
Family: Haloragaceae

Whorled milfoil is a mostly underwater native plant with a flower spike that rises above the water. Like other aquatic milfoils, whorled milfoil has underwater leaves arranged in whorls around the stem. Each leaf is feather-like and consists of paired, thread-like leaflets. The above water leaves (on the flower stalks) are located below each flower and are much smaller than the underwater leaves, although larger than the flowers.

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Leaf: Two types. The feather-like submersed leaves are 0.5-5 cm long and arranged in whorls around the stem with 4-5 leaves per whorl. The thread-like, paired leaflets are up to 10 mm long and range from 7-17 leaflets per leaf. The deeply-divided emergent leaves (on the flower stalk) are arranged in whorls around the stalk and are 2-10 mm long with the lower leaves usually larger than the upper leaves. The emergent leaves are longer than the flowers.

Stem: The stem is not highly branched and grows to 3m long. 

Flower: The tiny flowers have 4 petals and occur in the leaf bases on the emergent stalks. The emergent flower spikes (stalks) are 5-12 cm long with male flowers located at the top of the spike, bisexual and female flowers below. 

Fruit: The small fruit splits into 4 chambers with each chamber containing one seed.

Root: Rhizomes give rise to numerous smaller thinner roots.

Propagation: Plant fragments, rhizomes, seeds, and winter buds.

Importance of plant: Whorled milfoil provides habitat for aquatic invertebrates, which in turn provide food for fish and wildlife.

Distribution: North America, Europe, Asia, North Africa.

Habitat: Lakes, ponds, ditches, and small streams.

May be confused with: Most other water-milfoil species. The underwater growth of whorled milfoil is easily confused with Eurasian milfoil (M. spicatum), northern milfoil (M. sibiricum), and Andean milfoil (M. quitense). When flowering, the size and shape of leaves on the emergent flowering stalk and presence and shape of winter buds at the end of the growing season can distinguish these milfoil species. Otherwise, chemical analyses are needed to reliably distinguish them. 

Photographs: None available 

Line Drawings: None available 

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