This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Myriophyllum verticillatum L. Sp. Pl. 992. 1753.
Submerged leaves in crowded whorls of 3's and 4's, the capillary divisions very slender, sometimes finer than those of M. spicatum, about 10 pairs, 1'-1 1 /2' long, often minutely scabrate. Floral leaves pectinate or pectinate-pinnatifid, longer or shorter than the flowers; spike 2'-6' long; petals of the staminate flowers 4, purplish; stamens 8; fruit 1"-\\" long, and about 1" thick, somewhat gibbous at the base.
In both deep and shallow water, Quebec and Ontario to New York, west to Minnesota and British Columbia. Also in Europe and Asia. Myriad-leaf.
Submerged leaves usually in whorls of 3-5, occasionally scattered, the pinnate divisions capillary, 3"-5" long. Spikes short, 1'-2' long, numerous or several on the branching stems; uppermost floral leaves ovate or linear, entire or minutely toothed, smaller than the flowers, early deciduous; flowers mostly in pairs or solitary; petals of the staminate flowers 4, longer than the stamens, pale rose-color, deciduous; stamens 8; fruit nearly 1" long, slightly less than 1" thick; carpels rounded on the back, with a deep groove between them.
In deep water, Newfoundland to eastern Massachusetts and Ontario. Greenland. Common in Europe.
Stems slender, scape-like, nearly leafless, simple, erect, 1 1/2'-6' or "rarely 12' high. Rhizome creeping, sending up many sterile stems; flowers alternate, solitary; uppermost bracts obovate, often longer than the monoecious flowers, the lower oblong, often shorter, the lowest minute or wanting; petals 4, purplish, longer than the 4 stamens; fruit i" long and about as thick at the top, sometimes enlarged at the base; carpels rounded or obtusely angled on the back, separated by a shallow groove.
Sandy bottoms of ponds and streams, Newfoundland to New Jersey, Pennsylvania, Ontario and Michigan.
Typical form terrestrial, 1'-1 1/2' high, rooting in mud on shores. Leaves linear, entire or pectinate. Floating forms with stems often 12' long, branched, with all or most of the leaves pectinate into capillary segments; these produce the typical form if they take root; petals 4, purplish; stamens 4; fruit usually less than 1" long and about as thick at base, its carpels smooth, or rarely slightly roughened, separated by a shallow groove.
In ponds, Maine to Rhode Island, Maryland and recorded west to Illinois and Tennessee. Variable in appearance, but the variations are manifestly only conditions of the plant dependent upon its environment.
Myriophyllum heterophyllum Michx. Fl. Bor. Am. 2: 191. 1803.
Floral leaves in whorls of 3's to 5's, linear, ovate or lanceolate, serrate or rarely entire, much longer than the flowers. Submerged leaves subverticillate or scattered, crowded, pectinate-pinnatifid, about 10" long, the divisions 6-10 pairs, capillary; flowering spike elongated (sometimes 18' long); petals 4; stamens 4, rarely 6; fruit 1" long, and slightly longer than thick; carpels 2-keeled on the back, their sides convex, usually slightly scabrous.
In ponds, Ontario and New York to Florida, west to Minnesota, Texas and Mexico.
Myriophyllum hippuroides Nutt., with narrower floral leaves and fruit slightly longer, a species of the Pacific United States, is recorded from southern Ontario.