16 NORTH AMERICAN FLORA [VoLumy 17 
1. Potamogeton natans L. Sp. Pl. 126. 1753. 
Potamogeion natans prolixus Koch, Syn. Fl. Germ. & Helv. ed. 2. 775. 1844. 
Potamogeton floridanus Small, F1. SE. U. S. 37. 1903. 
Stem simple or sparingly branched, scarcely 1 m.long; floating leaves petioled; blades 
coriaceous, revolute, lanceolate-ovate or elliptic-ovate, 4.8-10.1 cm. long, 2.4-5.6 cm. wide, 
obtuse and mucronate or acute at the apex, cordate or narrowly acute at the base; petioles 
as long as the leaf-blades or longer; stipules 4-7 cm. long, acute, 2-keeled, axillary and 
free from the petiole; submerged leaves reduced to phyllodia, terete, scarcely 1.5 mm. 
thick and 10-25 cm. long, deciduous; spikes 3-5 cm. long, cylindric, densely-flowered ; 
peduncles 3-9 cm. long, as thick as the petiole; nutlets pitted on both sides, grooved on 
the back; embryo an incomplete spiral, the straight apex pointing towards the base. 
TYPE LOCALITY: Europe. 
DISTRIBUTION : Nova Scotia to British Columbia, south to New Jersey, Pennsylvania, Mis- 
souri, Nebraska, and southern California; apparently i in Florida (P. floridanus) ; also in Europe 
and Asia. 
ILLUSTRATIONS: Mem. Torrey Club 3?: p/. 25; Britt. & Brown, Ill. Fl. f. 722; nad Pflan- 
zenteich 41: f. 13; Linnaea 2: p/. 6, f. 20; Fl. Dan. pl. 1025 (poor) ; Engl. Bot. pl. 1822 
P. floridanus ‘Small is apparently an immature form of the above, with slender stem and 
leaves acute at both ends; mature fruit is unknown. 
2. Potamogeton Oakesianus Robb. in A. Gray, Man. ed. 5. 485. 1867. 
? Potamogeton Purshti Tuckerm. Am. Jour. Sci. II. 6: 228. 1848. 
Stem sometimes much branched ; floating leaves petioled ; blades coriaceous, revolute, 
elliptic-lanceolate or ovate-lanceolate, acute at the apex, and acute, or rounded and sub- 
cordate, at the base, 3.2-4.9 cm. long, 1-2.8 cm. wide petioles mostly 2-3 times aslong as 
the leaf-blades or shorter ; stipules acute, 2.5-4 cm. long, axillary and free from the petioles; 
submerged leaves reduced to phyllodia, terete, scarcely 1.5 mm. thick and often greatly 
elongated; spikes cylindric, 2-3.1 cm. long; peduncles 3-6 cm. long, twice thicker than 
the petioles; nutlets smooth on both sides, 3-keeled on the back ; embryo an incomplete 
spiral, the apex pointing towards the base. 
TYPE LOCALITY: Eastern Massachusetts. 
DISTRIBUTION: Maine to Wisconsin, south to New Jersey. 
ILLUSTRATIONS : Mem. Torrey Club 32: pL. 26; Britt. row, I. Fl. f 147. 
3. Potamogeton lateralis Morong, Bot. Gaz. 5: 51. 1880. 
Stem slender, much branched; floating leaves petioled; blades coriaceous, elliptic- 
lanceolate, acute or obtuse at the apex, narrowly decurrent at the acute base, 6.5-11 mm. 
long, 1.8-3.1 mm. wide; petioles as long as the leaf-blades or shorter; stipules axillary and 
free from the petioles, obtuse, 2.2-4 mm. long; submerged leaves capillary, 0.4-0.9 mm. 
wide, 1.8-3.4 em. long; spikes 2.4-6 mm. long, few-flowered; peduncles 9-15 mm. long, 
as thick as the stem; nutlets smooth, 2-grooved on the back ; embryo an incomplete spiral, 
the straight apex pointing directly towards the base. 
TYPE LOCALITY: Dedham, Massachusetts. 
DISTRIBUTION: Massachusetts and Connecticut. 
ILLUSTRATIONS: Mem, Torrey Club 3?: £1. 52; Britt. & Brown, Ill. Fl. f. 167. 
4. Potamogeton Vaseyi Robb. in A. Gray, Man. ed. 5. 485. 1867. 
Potamogeton Vaseyi latifolius Morong, Mem. Torrey Club 3?: 44. 1893. 
Stem slender, much branched; floating leaves petioled; blades coriaceous, spatulate- 
ovate, 7-12 mm. long, 4-6-mm. wide, rounded at the apex, acute and narrowly decurrent 
at the base; petioles as long as the leaf-blades or shorter; stipules axillary and free from 
the petioles, acute, 3-5 mm. long; submerged leaves slender, capillary, 0.5-0.9 mm. wide, 
2-3.6 cm. long; spikes sometimes interrupted, 5-11 mm. long; peduncles 5-14 mm. long, 
as thick as the stem ; nutlets smooth or slightly pitted, 3-keeled ; embryo a complete spiral, 
the curved apex pointing inside the base. 
TYPE LOCALITY: Near Ringwood, McHenry County, Illinois. 
DISTRIBUTION: Quebec to Wisconsin, south to southern New York. 
ILLUSTRATIONS : Mem. Torrey Club 3; pl. 51; Britt. & Brown, Ill. Fl. f. 166; Engler, Pflan- 
zenreich 411: f, 14 d-e. 
