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Aquatic and Wetland Vascular Plants of the Northern Great Plains

29. Haloragaceae, the Water Milfoil Family

1. Myriophyllum L. -- Water milfoil

1. Myriophyllum exalbescens Fern.

Submersed aquatic with stems simple to freely branched, whitened when dried, elongate and flexuous, 2-10(15) dm long; winter buds with reduced blackish leaves and shortened internodes often produced from lower nodes in late summer and fall, present through spring. Leaves in whorls of 3-4, pinnately dissected, with 5-10(12) filiform segments on each side of the midrib, (0.7)1-3 cm long; lower and middle nodes mostly 1 cm or more apart. Flowering spikes red or reddish-purple, clearly distinct from the submersed portion of the stem, 3-10(14) cm long, the floral bracts much smaller than the leaves, oblong to obovate, all or at least the upper bracts entire, mostly shorter than the flowers and fruits, only the lower ones sometimes denticulate and slightly longer; bracteoles ovate, entire. Flowers imperfect, the upper male and the lower female; petals present in male flowers, lacking in female flowers, oblong-obovate, concave, 1.5-3 mm long; stamens 8, the yellowish-green anthers conspicuous at anthesis. Fruits olive, subglobose, 2-4 mm long, the mericarps rounded on the back, smooth or rugulose. Jun--Sep. Shallow to deep water of lakes, ponds, marshes, ditches and sluggish streams; common and often abundant, the numerous reddish spikes often conspicuous on the water surface; (Boreal in N.Amer., s to MD, OH, IN, TX, NM and CA).

The Eurasian M. spicatum is introduced and spreading in e U.S. It is very similar to M. exalbescens but differs in having leaves more finely divided, with 12-24 filiform segments on each side of the midrib, and larger floral bracts, among other traits. The more aggressive nature of Eurasian milfoil makes it a potential menace in recreational waters. Thus far it has been detected as close to our region as central Minnesota.

Myriophyllum exalbescens, upper stem and inflorescence.
GIF- Distribution Map

Map key

Return to Family -- Haloragaceae - The Water Milfoil Family
Next Species -- Myriophyllum heterophyllum Michx.

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