Northern Prairie Wildlife Research Center
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.
Return to Family -- Haloragaceae - The Water
Milfoil Family
Next Species -- Myriophyllum heterophyllum Michx.
U.S. Department of the Interior |
U.S. Geological Survey
