| Author | Michaux | |
| Distribution | Coastal 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. | |
| Abundance | Frequent to common in the Coastal Plain; exceedingly rare westward. Often abundant where found; plants may choke waterways or cover surfaces of small impoundments. | |
| Habitat | Acidic, blackwater impoundments, beaver ponds, sluggish backwaters, canals, ponds, lakes, interdune ponds. |
| Phenology | Flowering and fruiting late April-October. | |
| Identification | Variable-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 Comments | None
| |
| Other Common Name(s) | Southern Water-milfoil, Two-leaf Water-milfoil, Variable-leaf Milfoil | |
| State Rank | S3? [S4] | |
| Global Rank | G5 | |
| State Status | | |
| US Status | | |
| USACE-agcp | OBL link |
| USACE-emp | OBL link |
