18 NORTH AMERICAN FLORA VoLuME 17 
8. Potamogeton mexicanus A. Benn. Jour. Bot. 25: 289. 1887. 
Stem simple; floating leaves petioled; blades coriaceous, elliptic-lanceolate, acute at 
both ends, 5.3-10 em. long, 1.6-2.8 cm. wide, sometimes revolute; petioles as long as the 
blades or longer; stipules axillary and free from the petioles, 2.5-3.4 em. long, acute; 
submerged leaves petioled; blades oblong-lanceolate or elliptic, acute or acuminate at the 
apex, narrowed at the acute base, 6.5-11 cm. long, 2.5-3.1 cm. wide; petioles as long as 
the blade or shorter ; spikes cylindric, few-flowered, 3-3.5 cm. long; peduncle as thick as 
the petioles or thicker, 4-6.5 cm. long; nutlets 3-keeled, the middle keel denticulate, the 
smaller lateral keels tuberculate ; embryo an incomplete spiral, the straight apex pointing 
directly toward the base. 
TYPE LOCALITY: Valle de Myrica, Mexico. 
DISTRIBUTION : Known only from the type locality and from San Luis Potosi. 
ILLUSTRATION : Mem. Torrey Club 32: p12. 33. 
9. Potamogeton amplifolius Tuckerm. Am. Jour. Sci. 
II. 6: 225. 1848. 
?P, amplifolius ovalifolius Morong; A, Benn. Jour, Bot. 42: 70. 1904. 
Stem simple or sparingly branched ; floating leaves petioled ; blades coriaceous, 32-40- 
nerved, ovate or elliptic-ovate, acute or acuminate at the apex, rounded or subcordate at 
the base, 6-10.5 cm. long, 2.7-5.1 cm. wide, in rare forms longer and wider; petioles 8-13 
cm. long; stipules acute, 2-keeled, sometimes 10 cm. long, usually shorter ; submerged leaves 
of two kinds, the upper elliptic or ovate, the lower lanceolate or sometimes falcate, 6~10.5 
em. long, 2.7-5.1 cm. wide; petioles 1-3.5 cm. long, usually winged ; spikes cylindric, 2.5-4.9 
cm. long, densely-flowered ; peduncles 5-18 cm. long, twice as thick as the petioles of the 
floating leaves; nutlets smooth, 3-keeled, the middle keel larger than the lateral ones; 
embryo a complete spiral, the curved apex pointing inside the base. 
TYPE LOCALITY: Cambridge, Massachusetts. 
DISTRIBUTION: New Brunswick to British Columbia, south to Georgia and Nebraska; reported 
also from Florida and Alabama. 
ILLUSTRATIONS : Mem. Torrey Club 3?: f/. 27; Britt. & Brown, Ill. Fl. f. 144. 
10. Potamogeton angustifolius Berch. & Presl, Rostlin. 
2: Alismac.19. 1821. 
Potamogeion heierophylius elongatus Mert. & Koch, in Rohling, Deuts. Fl. ed. 3. 1: 845. 1823. 
Potamogeton Zizti Roth, Enum. Pl. Germ. 1: 531, 1827. 
Potamogeton lucens connecticutensis Robb. in A. Gray, Man. ed. 5. 488. 1867. 
Potamogeton angustifolius methyensis Morong, Mem. Torrey Club 32: 30. 1893. 
Potamogeton angustifolius connecticutensis A. Benn. Jour. Bot. 39: 199. 1901. ; 
Potamogeion Zizit porrectifolius A, Benn.; Asch. & Graebn. in Engler, Pflanzenreich 4: 83, 
1907. 
Potamogeton Zizti gracilis A, Benn.; Asch. & Graebn. in Engler, PAlanzenreich 411 : 83, -1907. 
Stems branching; floating leaves petioled, sometimes wanting; blades coriaceous, 
rarely somewhat translucent, elliptic-ovate or elliptic, acute or acuminate or sometimes mu- 
cronate at the apex, narrowed at the acute base, 3.5-9 cm. long, 1.5-3.8 cm. wide; petioles 
shorter than the blades or longer ; submerged leaves sessile or the upper petiolate; blades 
pellucid, lanceolate or somewhat spatulate, and minutely serrulate towards the acute, some- 
times cuspidate apex, 5-15 cm. long, 0.5-2.8 cm. wide, or rarely wider; primary nerves 7, 
sometimes with a few intermediate secondary nerves; stipules 2-keeled, obtuse, 1.3-3 cm. 
long, axillary and free from the petioles; spikes cylindric, 2.3-4.5 cm. long, densely flow- 
ered, rarely interrupted ; peduncles as thick as the stem or thicker, 6-12 cm. long; nutlets 
smooth, 3-keeled when mature; embryo mostly an incomplete spiral, the apex pointing 
directly towards the base or sometimes inside it. 
TYPE LOCALITY: Bohemia. : ; ; 
DISTRIBUTION: Maine to California, south to Florida, Mexico, and Guatemala; also in 
Europe. . east 
Ti UepeaniONa: Mem. Torrey Club 32: £/. 37; Britt. & Brown, Ill. Fl. f. 153 (as P. Ziz7t). 
The varieties listed in the synonymy represent forms differing widely, but not persistently, 
from the type. The variations being of the vegetative rather than the reproductive organs, they 
can not be treated specifically. 
