70 NAIADACEAE 



Montane region at 5000 to 7000 feet alt. : Bear Valley, San Bernardino Mts., 

 Parish; Sierra Nevada; Mt. Shasta; northward to British Columbia and east 

 to the Atlantic. Europe, Asia. 



Befs. POTAMOGETON NATANS L. Sp. PL 126 (1753); Wats. Bot. Cal. 2: 195 (1880); 

 Morong, Mem. Torr. Club, 3 2 : 13, pi. 25 (1893). 



2. P. epihydrus Raf. Stems slender (y% line broad), compressed, mostly 

 simple, 1 to 2 feet long ; floating leaves narrowly oblong, 1% to 2 inches long, 

 gradually narrowed into petioles about y 2 as long; submerged leaves thin, 

 grass-like, 2 to 3 inches long, 2 to 3 lines wide, the petiole-like base very short ; 

 spikes dense, ^ inch long, on peduncles l 1 ^ to 1% inches long ; nutlet flattish, 

 3-keeled, the seed impressed on the sides. 



Yosemite Valley (Bolander 6393), north to British Columbia and east to the 



Atlantic States. 



Eefs. POTAMOGETON EPIHYDRUS Eaf. Med. Eepos. 2d ser. 5: 354 (1808). P. nuttallii C. & 

 S. Linnaea, 2: 226 (1827). P. claytpni Tuckerm. Am. Jour. Sci. 1st ser. 45: 38 (1843) ; Wats. 

 Bot. Cal. 2: 195 (1880). 



3. P. dimorphus Raf. Stems simple, l 1 /^ feet long; floating leaves in 2 or 

 3 opposite pairs, oblong, tapering to each end, impressed beneath with 7 to 9 

 nerves. 3 to 4 lines wide and 7 to 10 lines long, passing rather definitely at base 

 into the somewhat shorter (or sometimes longer) petiole; submerged leaves 

 14 to % line wide, 1 or 2 inches long, acute at tip but not setaceous, stipules 



1 to 5 lines long, adnate for about % their length; flowers in a few-flowered 

 head (or the emersed in a very short spike), the peduncles 1 to 3 lines long, 

 shorter than the submersed spike ; nutlet less than 1 line long, keeled on the 

 back, the keel winged and sometimes denticulate; embryo coiled 1% times; 

 pericarp very thin and fleshless, revealing clearly the coiled embryo, the whole 

 suggestive of a snail shell." 



Lake Surprise, San Jacinto Mts., alt. 9000 feet, Hall 2490; near Visalia 

 ace. Bot. Death Valley; irrigating ditches at Turlock. Missouri to Virginia 

 and Nova Scotia. 



Eefs. POTAMOGETON DIMORPHUS Eaf. Am. Mo. Mag. 1: 358 (1817). P. spirillus Tuckerm. 

 Am. Journ. Sei. 2d ser. 6: 228 (1848) ; Morong, Mem. Torr. Club, 3 2 : 49, pi. 56 (1893). 



P. HYBRIDUS Michx. Very similar to P. dimorphus but peduncles equaling 

 or longer than submersed spike, frequently recurved; keels toothed. Credited 

 to California by Taylor (N. Am. PI. 17 1 : 17). 



4. P. alpinus Balbis. ALPINE PONDWEED. Whole plant of a reddish tinge; 

 stems simple, 1 or 2 feet long; floating leaves narrowly oblong, tapering at 

 both ends, 2 to 4 inches long, % to % inch wide, submerged leaves 2 to 7 inches 

 long, !/4 to y 2 inch wide, all sessile or narrowed to a short petiole; stipules 

 broad, V 2 to 1*4 inches long; spikes % to 1% inches long, on peduncles about 



2 inches long; nutlet with a distinct pit on each side. 



Ponds in the high mountains: Sierra Nevada, North Fork of Kings River, 

 7000 feet alt., Hall & Chandler; Silver Valley, Alpine Co., 7200 feet alt., 

 Brewer 1978; north to Alaska and east to Florida and Labrador. Europe, 

 Asia. 



Eefs. POTAMOGETON ALPINUS Balbis, Misc. 13 (1804); Morong, Mem. Torr. Club, 3 Z : 19, 

 pi. 30 (1893). P. rufescens Sehrader; Chamisso, Adnot. Fl. Berol. 5 (1815) ; Wats. Bot. Cal. 

 2: 195 (1880). 



5. P. americanus C. & S. Stems terete, much branched, 3 to 6 feet long; 

 floating leaves coriaceous, elliptical, 2 to 4 inches long, y 2 to l l / 2 inches wide, 

 the petiole often longer than the blade, submerged leaves very thin, lanceolate, 





