This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", 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..
Stems, flowers and leaf-buds all at first enclosed in a hyaline envelope, corresponding to the stipule in Potamogeton. Staminate and pistillate flowers in the same axil; the staminate solitary, consisting of a single 2-celled anther, borne on a short pedicel-like filament; the pistillate 2-5. Ovary flask-shaped, tapering into a short style; stigma broad, hyaline, somewhat cup-shaped, its margins angled or dentate. Fruit a flattish falcate nutlet, ribbed or sometimes toothed on the back. Embryo bent and coiled at the cotyledonary end. [In honor of J. H. Zannichelli, 1662-1729, Italian physician and botanist.]
Zannichellia palustris L. Sp. PI. 969. 1753-Z. intermedia Torrey; Beck Bot. 385. 1833.
Stems capillary, sparsely branched, the rhizome creeping, the roots fibrous. Leaves 1' - 3' long, 1/4" or less wide, acute, thin, 1-nerved with a few delicate cross-veins; spathe-like envelope separate from the leaves and fruits at maturity; fruits 2-6 in a cluster, 1"-2" long, sometimes sessile, sometimes pedicelled, sometimes the whole cluster peduncled; style persistent, 1/2"-1" long; plant flowering and ripening its fruit under water.
In fresh or brackish water, nearly throughout North America, except the extreme north. Widely distributed in the Old World. July-Sept.