66 NAIADACEAE., 
With propagating buds or glands, or both. 
With buds, but without glands. 
Leaves serrulate, 3-7-nerved. 18. P. crispus. 
Leaves entire, with 3 panera and many fine nerves. 19. P. zosteracfolius. 
Commonly with glands, but no buds. 
Stems long-branching from the base; leaves lax, flat, Saprmed, abruptly acute or 
cuspidate. , PD. Fistiai. 
Stems simple; leaves strict, revolute, 3-5-nerved, acuminate. a P. rutilus, 
With both buds and glands. 
Glands large and translucent; buds rare. 22. P. obtusifolius. 
Glands small, often dull; buds common. 
Leaves linear, 5-7-nerved. 23. P. Friesit. 
Leaves linear, 3-nerved. 27. P. pusillus. 
Leaves capillary, 1-nerved or nerveless. 23. P. gemmiparus. 
Stipules adnate to the leaves or petioles. 
With both floating and submerged leaves. 
Submerged peduncles as long as the spikes, clavate, often recurved. 29. P. diversifolius. 
Submerged peduncles none, or at most hardly a line long. 30. P. Spirillus. 
With submerged leaves only. 
Stigma broad and sessile. 31. P. filiformis. 
Style apparent; stigma capitate. 
Fruit without keels or obscurely keeled. 32. P. pectinatus. 
Fruit strongly 3- keeled. 
Leaves entire, 3-5-nerved. 33. P. interruptus. 
Leaves minutely serrulate, finely many-nerved. 34. P. Robbinsii. 
1. Potamogeton natans I,. Common Floating Pondweed. (Fig. 142.) 
Potamogeton natans I,. Sp. Pl. 126. 1753- 
Stems 2°-4° long, simple or sparingly branched. 
Floating leaves thick, the blade ovate, oval or ellip- 
tic, 2/-4’ long, 1/-2’ wide, usually tipped with a 
short abrupt point, rounded or subcordate at the 
base, many-nerved; submerged leaves reduced to 
phyllodes or bladeless petioles which commonly 
perish early and are seldom seen at the fruiting 
period; stipules sometimes 4’ long, acute, 2-keeled; 
peduncles as thick as the stem, 2’-4’ long; spikes 
cylindric, very dense, about 2’ long; fruit turgid, 
2//-2%/’ long, about 14’ thick, scarcely keeled, 
narrowly obovoid, slightly curved on the face; 
style broad and facial; nutlet hard, more or less 
pitted or impressed on the sides, 2-grooved on the 
back; embryo forming an incomplete circle, the 
apex pointing toward the base. 
In ponds and streams, throughout North America ex- 
cept the extreme north, extending into Mexico. Also 
in Europe and Asia. July-Aug. 
2. Potamogeton Oakesianus Robbins. Oakes’ Pondweed. (Fig. 143.) 
Potamogeton Oakesianus Robbins in A. Gray, Man. 
Ed. 5, 485. 1867. 
Stems very slender, often much branched from 
below. Floating leaves elliptic, mostly ob- 
tuse, rounded or slightly subcordate at the 
base, 1/-2’ long, 5’/-9/’ wide, 12-20-nerved; 
petioles 2’-6’ long; submerged leaves mere cap- 
illary phyllodes, often persistent through the 
flowering season; peduncles 1/-3’ long, com- 
monly much thicker than the stem, mostly soli- 
tary; spikes cylindric, %’—1’ long; stipules acute, 
hardly keeled; fruit obovoid, about 14’ long, 1/’ 
thick, nearly straight on the face, 3-keeled, the 
middle keel sharp; style apical or subapical; sides 
of the nutlet not pitted, but sometimes slightly 
impressed; embryo circle incomplete, the apex 
pointing toward the base. J 
In still water, Anticosti to northern Pennsylva- 
nia and New Jersey. Summer. 
