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..
Potamogeton varians Morong; Fryer, Jour. Bot. 27: 33. 1889.
Stems many, branched, 2°-3° long. Floating leaves obovate or elliptic, abruptly acute at the apex, rather thin, 13-23-nerved, 1 -2 1/2' long, 6"-13" wide, borne on slender petioles; submerged leaves pellucid, spatulate-oblong or linear-lanceolate, 2'-4' long, 3"-9" wide, 5-13-nerved, cuspidate or spines-cent, sessile or subsessile, often reduced to phyl-lodes with a very narrow blade and a long acumi-nation at the'base and apex; peduncles often thickening upward, 1'-2' long; stipules obtuse, faintly keeled, the apex slightly hooded; spikes large; fruit about 1" long, roundish or obliquely ovoid, obscurely 3-keeled, with a curved or slightly angled face; embryo with the apex pointing slightly inside of the base.
In Mystic Pond, Medford. Mass. Also in Europe. Summer. Apparently a mere form of the preceding, or perhaps a hybrid between P. angustifolius and P. heterophyllus.
Potamogeton illinoensis Morong, Coult. Bot. Gaz. 5: 50. 1880.
Stems stout, much branched above. Floating leaves opposite, numerous, thick, 4'-5 1/2' long, 2'- 3 1/2' wide, many-nerved, oval or broadly elliptic, short-pointed at the apex, rounded, subcordate or narrowed at the base; petioles 1'-4' long; submerged leaves numerous, 4'-8' long, 1'-2' wide, 13-19-nerved, acuminate or the uppermost acute, mostly tapering at the base into a short broad flat petiole, rarely reduced to phyllodes; stipules 2'-3' long, obtuse, strongly 2-carinate; peduncles 2'-4' long; spikes 1'-2' long; fruit roundish or obovoid, 1 1/2"-2" long, 1"-1 1/2" thick, dorsally 3-keeled; style short, blunt.
In ponds, Illinois to Iowa and Minnesota. Aug.
P. angustifolius Berch. & Presl, Rost. 19. 1821.
Potamogeton lucens connecticutensis Robbins in A. Gray, Man. Ed. 5, 488. 1867.
Potamogeton angustifolius var. Methyensis A. Bennett, Journ. Bot. 29: 151. 1891.
Stems slender, branching. Floating leaves elliptic, 1 1/2'-4' long,6"-12" wide, many-nerved; petioles mostly short; submerged leaves mostly lanceolate or oblanceolate, thin, acute or cuspidate, 2'-6' long, 3"-15" wide, 7-17-nerved; stipules 6"-18" long, obtuse, 2-keeled; peduncles thicker than the stem, 2 1/2'-6' long; spikes 1'-2' long; fruit obliquely obovoid, 1 1/4"-2" long, about 1" thick, the face dorsally 3-keeled; style short, blunt, facial; apex of the embryo pointing directly to the base.
In lakes and streams, Quebec to California, Florida and Wyoming. Also in Europe. July-Aug.