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..
Sparganium natans submuticum Hartm. Handb. Skand. Fl. ed. 4: 312. 1843.
Sparganium hyperboreum Laest.; Beurl. Oefvers. Vet. Akad. Foerh. 9: 192. 1852.
Stem floating and elongated, or decumbent, or ascending and 4'-8' high; leaves light green, very narrow, 1/2'-2" wide, flat or slightly round-keeled near the base, in the case of floating plants sometimes greatly elongated; leaf-sheaths slightly dilated near the base, but not scarious-margined; pistillate heads 2-4, the lower 1 or 2 usually peduncled and supra-axillary; fruiting heads 4"-5" in diameter; nutlets dark-yellow, dull, the body ellipsoid; stigma oval.
In ponds and streams, Greenland to Newfoundland, Hudson Bay and Alaska Also in northern Europe and Asia. July-Sept.
Sparganium natans Oeder. Fl. Dan. 25: 5. 1764. Not S. nutans L. 1753. Sparganium minimum Fries, Summa Veg. Scand. 2: 560. 1849. Sparganium angustifolium A. Gray, Man. Ed. 5, 430. 1856. Not S. angustifolium Michx. 1803.
Stem floating and sometimes elongated, or decumbent, ascending or erect, and relatively short; leaves dark-green, narrow, mostly 1"-3 1/2" .wide, flat; upper leaf-sheaths somewhat dilated, but not scarious-margined; pistillate heads solitary, or 2 or 3 and placed about equally distant, axillary; fruiting heads about 5" in diameter; nutlets greenish-brown, dull, the body broadly ellipsoid, usually constricted below the middle; stigma obliquely oblong or oval.
In ponds and streams, Labrador to Alaska, New Jersey, Tennessee ( ?), Utah and Oregon. Also in Europe and Asia. June-Aug.