Illinois Pondweed

Potamogeton angustifolius Berch. & Presl, Rostlin
2 : Alismac. 19. 1821.
Potamogeton heierophyllus elongatus Mert. & Koch, in Rohling, Deuts. Fl. ed. 3. 1 : 845. 1823.
Potamogeton Zizii Roth, I$num. PI. Germ. 1 : 531. 1827.
Potamogeton lucens connecticutensis Robb. in A. Gray, Man. ed. 5. 488. 1867.
Potamogeton angustifolius methyensis Morong, Mem. Torrey Club 3 2 : 30. 1893.
Potamogeton angustifolius connecticutensis A. Benn. Jour. Bot. 39 : 199. 1901.
Potamogeton Zizii porrectifolius A. Benn.; Asch. & Graebn. in Bugler, Pflanzenreich 4 11 : 83.
1907. Potamogeton Zizii gracilis A. Benn.; Asch. & Graebn. in Engler, Pflanzenreich 4 1 * : 83. 1907.
Stems branching; floating leaves petioled, sometimes wanting; blades coriaceous, rarely somewhat translucent, elliptic-ovate or elliptic, acute or acuminate or sometimes mucronate 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 p etiolate ; blades pellucid, lanceolate or somewhat spatulate, and minutely serrulate towards the acute, sometimes 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 flowered, 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

Potamogeton illinoensis Morong, Bot. Gaz. 5 : 50. 1880
+
Stem branched ; floating leaves petiolate ; blades coriaceous, thick, ovate or elliptic-
t
ovate, mucronate at the apex, rounded or subcordate at the base and sometimes decurrent, 8-14 cm. long, 4-8 cm. wide ; petioles 6-10 cm. long, sometimes winged ; submerged leaves petioled ; blades mostly lanceolate-oblong, acute or acuminate at the apex and narrowed or sometimes decurrent at the base, 8-18 cm. long, as wide as or a little wider than the floating leaf -blades ; petioles winged, 1-2.8 cm. long, rarely longer ; stipules 2.5-4.5 cm. long, obtuse, 2-keeled; spikes cylindric, many-flowered, 2.5^.8 cm. long; peduncles as thick as or thicker than the stem, 5-9 cm, long ; nutlets smooth, 3-keeled, the middle keel sharper and more prominent than the smaller lateral ones ; embryo a complete spiral,, the curved apex pointing inside the base.
Type locality : Oquawka, Illinois.
Distribution : Western Illinois and eastern Iowa.