NAIADACEAE (PONDWEED FAMILY) 



.-it petioles about equaling the blade; submerged leaves often very 



mostly falcate and somewhat undulate, acute, attenuate to a usually 



short petiole: spike thick, on a very stout peduncle: fruit large, 3-keeled, with 



a l.n.a.l, Mout t.rak: sides of the nutlet not pitted. In ponds and streams; 



from N o to the Atlantic States; also in California and Oregon. 



:;. Potamogeton diversifolius Raf. Med. Rep. II. 5: 354. 1808. Floating 



oval to lance-oblong, often acute, longer than the filiform petioles, with 



about . beneath, deeply impressed; submerged leaves very numerous, 



almost setaceous, 2-10 cm. long, very rarely 1 mm. wide; stipules obtuse: 



1 spikes s-14 mm. long; submersed spikes 1-4-flowered, their .peduncles 



tof their own length) frequently recurved: fruit minute, about 8-toothed on 



the margin. Montana, probably Wyoming, east to New Brunswick and 



Florida. 



4. Potamogeton heterophyllus Schreb. Spicil. Fl. Lips. 21. 1771. Stems 

 very slender, branching: floating leaves rather thin, 9-15-nerved, small, oblong- 

 elliptic, acutish, rounded or cuneate at base, on slender petioles mostly equal- 

 ing or exceeding the blade; submerged leaves linear-lanceolate, variable in 

 length, more commonly short, acute or acuminate, narrowed at base: spikes 

 rather loose, on stout often elongated peduncles: fruit round-obovate, acute, 

 scarcely keeled. In still or flowing water; from the Yellowstone eastward; 

 also in Nevada and California. 



5. Potamogeton lonchites Tuckerm. Am. Journ. Sci. II. 6: 226. 1848. 

 Stem rather slender, branching: floating leaves thickish, 11-23-nerved, long 

 elliptical to oblong-lanceolate, acute or acutish, rather abruptly narrowed into 

 a petiole usually longer than the blade; submerged leaves thin and long, 

 mostly linear-lanceolate, attenuate at base, the lower sessile: spikes on stout 

 peduncles: fruit obliquely obovate, carinate, acute: nutlet somewhat 3-keeled, 

 the sides scarcely impressed. Usually in streams ; from Mexico to the Atlantic 

 States; also in the Pacific States. 



6. Potamogeton Zizii Roth, Enum. 1: 531. 1827. Stems branching, slender: 

 floating leaves many-nerved, narrowly elliptic, 4-10 cm. long, mostly acute, 

 short-petioled or often nearly sessile; submerged leaves lanceolate or ob lan- 

 ceolate, thin, acute, longer than the floating leaves, 7-17-nerved: peduncles 

 thicker than the stem, long: spike often 5 cm. long: fruit obliquely ovoid, 

 rather large, dorsally 3-keeled. Wyoming and Montana, east to the Atlantic 



States. 



7. Potamogeton alpinus Balbis, Misc. Bot. 13. 1804. Floating leaves 

 (often wanting) rather thin, 11-17-nerved, narrowly oblong-elliptic or ob- 

 lanceolate, acutish, attenuate into a very broad, short petiole; submerged 



is large as the floating, sessile or nearly so, narrowly oblong-lanceolate, 

 obtuse or acute: spikes rather slender, on stout often elongated peduncles: fruit 

 round-obovate, acutely margined, beaked by the rather long style: nutlet 

 pitted on each side. P. rufescens. In ponds and streams; Colorado to Mon- 

 tana, and in the Atlantic States. 



s. Potamogeton perfoliatus L. Sp. PI. 126. 1753. The large leaves long- 



lanceolatc from a cordate-clasping base, and acuminate, wavy, 8-12 cm. long: 



peduncles thickened upward: fruit irregularly obovate, obtusely margined, the 



nli a .-hallow indentation. P. perfoliatus lanceolatus. Colorado to 



Montana, thence across the continent. 



'.). Potamogeton lucens L. Sp. PL 127. 1753. Stem stout, branching: 



!\ lar-ri', o-15 cm. long, oblong-lanceolate or oblanceolate, abruptly 



>r acuminate, often undulate-serrate, narrowed at base to a short petiole 



<ir sub pules lurgc: peduncles often elongated: fruit acute, slightly 



keeled. [ >, \,.\ v Mexico to California; also eastward to Florida and New 



England. 



1<>. Potamogeton pusillus L. Sp. PL 127. 1753. Stem slender, flattish or 



cylindrical, often very branching: leaves narrow or setaceous-linear, 



acuminate, unit.- .,r subacute, 1-3-nerved, furnished with translucent glands 



'i sideal the base; stipules at first obtuse: spikes interrupted or capitate, 



\vered, on rather long peduncles: fruit obliquely elliptical, scarcely 



