Vascular Plants of North Carolina
Account for Variable-leaf Water-milfoil - Myriophyllum heterophyllum   Michaux
Members of Myriophyllum with account distribution info or public map:
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Section 6 » Order Haloragales » Family Haloragaceae
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AuthorMichaux
DistributionCoastal Plain and Sandhills; disjunct to Graham County in the low mountains (beaver pond above Santeetlah Dam). No doubt found in other Coastal Plain counties.

ME to southern Ont. and MN, south to FL and TX.
AbundanceFrequent to common in the Coastal Plain; exceedingly rare westward. Often abundant where found; plants may choke waterways or cover surfaces of small impoundments.
HabitatAcidic, blackwater impoundments, beaver ponds, sluggish backwaters, canals, ponds, lakes, interdune ponds.
See also Habitat Account for Coastal Plain Herbaceous Ponds and Sloughs
PhenologyFlowering and fruiting late April-October.
IdentificationVariable-leaf Water-milfoil has dull to bright red stems that float just below the water surface; each stem may be several yards long. Leaves are abundant and in closely spaced whorls, finely dissected into 15-31 (-37) threadlike divisions, greenish brown in color. Flowering shoots extend above the water on thick stalks that are generally covered with lance-shaped, green bracts. Dull green, 4-parted fruits grow at the bases of the bracts. M. pinnatum has only 9-15 (-17) leaf segments and its floral bracts are deeply dissected. M. laxum has only 7-15 (-17) leaf segments and its floral bracts are very short and barely longer than the flowers and fruits. BEWARE: Plants of M. heterophyllum, when in very shallow water or stranded, produce floral bracts that are sharply pinnate and much like those of M. pinnatum.
Taxonomic CommentsNone

Other Common Name(s)Southern Water-milfoil, Two-leaf Water-milfoil, Variable-leaf Milfoil
State RankS3? [S4]
Global RankG5
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