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..
Aquatic herbs, with verticillate or alternate leaves, the emersed ones entire, dentate or pectinate, the submerged ones pinnatifid into capillary segments, the axillary commonly monoecious 2-bracted flowers often interruptedly spicate. Upper flowers generally staminate with a very short calyx-tube, its limb 2-4-lobed, or none; petals 2-4; stamens 4-8 Intermediate flowers often perfect. Lower flowers pistillate, the calyx more or less deeply 4-grooved and with 4 minute lobes, or none; ovary 2-4-celled; ovule 1 in each cavity, pendulous; styles 4, short, often plumose. Fruit splitting at maturity into 4 bony 1-seeded indehiscent carpels which are smooth, angled or tuberculate on the back. [Greek, myriad-leaved.]
Carpels smooth or minutely papillose.
Stamens 8; petals fugacious.
Floral bracts verticillate.
Floral bracts entire or toothed, shorter than the flowers.
Floral bracts pectinate, shorter or longer than the flowers.
Floral bracts alternate.
Stamens 4; petals not fugacious.
Stem scape-like, erect, nearly leafless.
Carpels rough, tuberculate or ridged.
Flowers on emersed spikes.
Floral leaves ovate or lanceolate, serrate.
Floral leaves linear, pectinate.
Flowers on submersed stems.
Myriophyllum spicatum L. Sp. Pl. 992. 1753.
Submerged leaves in whorls of 4's and 5's, dissected into capillary divisions. Floral leaves (bracts) ovate, entire or serrate, usually shorter than the flowers; spike 1' - 3' long; petals 4, deciduous; stamens 8; stigmas short; fruit about 1" long and 1 1/2" thick; carpels rounded on the back, with a deep wide groove between them, smooth, or very rarely slightly rugose.
In deep water, Newfoundland to Manitoba, Alaska, Maryland, Michigan, Kansas, New Mexico and California. Also in Europe and Asia. Both this species and the next have been erroneously recorded from Florida. Meakin. Water-navelwort.