PONDWEED FAMILY 



85 



3. Potamogeton dimorphus Raf. 

 Spiral T'ondweed. Fig. 175. 



Potamogeton dimorj-hus Raf. Am. Month. Mag. 1: 338. 1817. 

 Potamogeton st^irillus Tuckerm. Am. Tourn. Sci. II. 6: 228. 

 1848. 



Stems 1-3 dm. long, compressed, branched, the 

 branches often short and recurved. Floating leaves 

 oval or elHptic, obtuse, the largest about 25 mm. 

 long and 1 cm. wide, with 5-13 nerves deeply im- 

 pressed beneath ; petioles often 25 mm. long ; sub- 

 merged leaves linear, 3-5 cm. long, about 1 mm. wide, 

 mostly 5-nerved ; stipules of the upper floating leaves 

 free, those of the submerged leaves adnate to the 

 lilade or petiole; emersed spikes 6-10 mm. long, 

 many-fruited, distinctly peduncled ;' submerged spikes 

 globular and nearly sessile, few-flowered; fruit 

 cochleate, roundish, less than 2 mm. long, flat and 

 deeply impressed on the sides, 3-keeled on the back, 

 the middle keel winged and rarely 4-5-toothed; 

 styles deciduous ; embryo spiral, about one and one- 

 half turns. 



In still, shallow water. Nova Scotia to Virginia, west to 

 Minnesota and California, where it occurs in the Sierra 

 Nevada and San Jacinto Mountains; Transition Zone. Type 

 locality: Pennsylvania. 



4. Potamogeton epihydrus Rat. 

 Nuttall's Pondweed. Fig. 176. 



Potamogeton epihydrus Raf. Med. Rep. II. 5: 354. 1808. 



Potamogeton nuttallii Cham. & Sch. Linnaea 2: 226. 



1827. 

 Potamogeton claytoni Tuckerm. Am. Journ. Sci. 45: 38. 



1843. 



Stems siiTiple or branched, slender, compressed, 

 1-2 m. long. Floating leaves elliptic, or obovate, 

 obtuse at the apex, narrowed at base, 3-8 cm. 

 long, 8-24 mm. wide, about 175-nerved; petioles 

 2-5 cm. long; stipules free from the petioles, ob- 

 tuse, 2-3 cm. long ; submerged leaves sessile, 

 linear or linear-lanceolate, 5-nerved, with a cel- 

 lular reticulation along the midrib, 6-14 cm. long, 

 3-4 mm. wide ; spikes cylindric, many-flowered, 

 1.5-6 cm. long; nutlets deeply pitted, 3-keeled, the 

 middle keel sharp ; embryo a complete spiral. 



In quiet streams and lakes, Boreal and Transition 

 Zones; Newfoundland to British Columbia, south to 

 North Carolina and central California. On the Pacific 

 Coast it is frequent in British Columbia and Washington, 

 but in California it is known only from Yosemite Valley. 

 Type locality: Canada. 



5. Potamogeton amplifolius Tuckerm. 

 Large-leaved Pondweed. Fig. 177. 



Potamogeton amplifolius Tuckerm. Am. Tourn. Sci. II. 

 6: 225. 1848. 



Stems long, simple or occasionally branched. 

 Floating leaves oval or ovate, abruptly pointed at 

 the apex, rounded at the base, 5-10 cm. long, 3-5 

 cm. wide, 32-40-nerved ; petioles 7-12 cm. long ; 

 stipules 2-keeled, 5-8 cm. long; submerged leaves 

 usually petioled, the upper often elliptic or oval, 

 S-15 cm. long, 3-6 cm. wide, the lower lanceolate, 

 sometimes falcate, often 20 cm. long, 3-5 cm. 

 wide ; petioles 1-3.5 cm. long, usually winged ; 

 spikes cylindric, 2.5-5 cm. long, densely flowered ; 

 peduncles 5-18 cm. long, twice as thick as the 

 petioles ; nutlets smooth, 3-keeled, the middle keel 

 larger than the lateral ; eml)ryo a complete spiral. 



Widely distributed over North America from Maine 

 to Puget Sound, south to Guatemala. On the Pacifiic 

 Coast ranging from British Columbia to the southern 

 Sierra Nevada, mainly in the Transition Zone. Type 

 Ujcality: Cambridge, Mass. 



