13 
Leaves narrowly linear, 3-nerved, acute at the apex. 
r i 4 sonnel 
Leaves with narrow blades, ML or setaceous, I-nerved or nerveles 
Peduncles terminal, v no lon 18. ашы 
Peduncles axillary, sh 19. Р. Curtissit, 
With propagating buds or eo or both. 
Leaves serrulate, 3-7-nerved. «P, erishbus, 
Leaves entire, with 3 principal and many fine nerves. 
21. P. zosterefolius. 
ee with glands, but no buds 
Stems long branching from the SE leaves lax, Ж ‚дйн abruptly 
P. НИ. 
acute or cuspidate. 
Stems simple, leaves strict, revolute, 3-5-nerved, acuminate, 
26. P.rutilus. 
уы both buds and glands, 
ands large and ETNE buds rare. 24. P. obtusifolius. 
Сон small, often dull, buds common. 
Leaves linear, 5-7-nerved. 25. P. major 
Leaves linear, 3-nerved. 29. P. pusillus. 
Leaves capillary, 1-nerved or nerveless. 30. P. gemmiparus. 
Stipes adnate to the leaves or petioles. 
ith floating and submerged leaves. 
Submerged peduncles as long as the spikes, clavate, often recurved. 
31. P. diversifolius. 
Submerged peduncles none, or at most hardly a line long. 
32. P. Spirillus. 
d and sessile. 33. P. filiformis. 
Style doceri, stigma ca 
Fruit without keels or o keeled. 
With nn leaves only. 
Stigm 
Leaves capillary, 1-nerved or nerveless. 34. Р. pectinatus. 
Leaves linear, 3-5-nerved. 35. Р. latifolius. 
Fruit strongly 3-keele 
Leaves entire, 3-5-nerved. 36. P. interruptus. 
Leaves minutely serrulate, finely many-nerved. 37- P. Robbinsü. 
1. POTAMOGETON NATANS, L. Sp. Pl. 126 (1753). 
The stems of this species grow from two to four feet in height, 
usually in still waters with a muddy bottom, and are simple or 
sparingly branched. Floating leaves thick, coriaceous, the blade 
ovate, oval or elliptical, 2-4 inches long and 1-2 inches broad, 
usually tipped with a short, abrupt point, rounded or sub-cordate 
at base, and with 20-30 rather strong nerves. The submerged 
leaves by which this species can always be distinguished from 
every other except P. Oakesianus, are phyllodia, without the 
