ZANNICHELLIACEAE. 



VOL. I. 



20. Potamogeton Hillii Morong. Hill's Pond- 

 weed. Fig. 193. 



Potamogeton Hillii Morong, Coult. Bot. Gaz. 6: 290. 1881. 



Stems slightly compressed, slender, widely branching, 

 l-2 long. Leaves linear, acute or cuspidate, or often 

 almost aristate, i'-2i' long, i"-ii" wide, 3-nerved, the 

 lateral nerves delicate and nearer the margins than the 

 midrib ; stipules whitish, many-nerved, obtuse, 3"-5" 

 long; peduncles about \' long, erect or slightly recurved, 

 more or less clavate; spikes capitate, 3-6-fruited; fruit 

 obliquely obovoid, obtuse at the base, about 2" long, 

 l"-ii" thick, 3-carinate on the back, the middle keel 

 sharp and more or less undulate, flat on the sides, face 

 slightly arched; style nearly facial, short; embryo coiled. 



In ponds, eastern New York to Michigan, south to 

 Pennsylvania and Missouri. There are two forms of the 

 species, the one 2-glandular at the base of the leaves, the 

 other glandless. July-Sept. 



21. Potamogeton foliosus Raf. Leafy Pondweed. Fig. 194. 



Potamogeton foliosus Raf. Med. Rep. (II.) 5 : 



354. 1808. 

 Potamogeton pauciflorus Pursh, Fl. Am. Sept. 



121. 1814. Not Lam. 1789. 

 Potamogeton niagarensis Tuckerm. Am. Journ. 



Sci. (II.) 7: 354- 1849- 

 Potamogeton foliosus niagarensis (Tuckerm.) 



Morong, Mem. Torr. Club, 3 : Part 2, 39. 



1893- 



Stems flattened, much branched, i-3 

 long. Leaves i'-3' long, i"-i" wide, acute, 

 3~5-nerved, not glandular at the base ; 

 stipules white, hyaline, obtuse or sometimes 

 acute, 6"-io" long; peduncles more or less 

 clavate, erect, about 4' long; spikes 4-12- 

 flowered; fruit lenticular or nearly orbic- 

 ular, about i" in diameter, 3-keeled on the 

 back, the middle keel winged, sinuate- 

 dentate, often with projecting shoulders or 

 teeth at each end, the face strongly angled 

 or arched, sharp, often with a projecting 

 tooth at the base ; style apical. 



In ponds and streams, New Brunswick to 

 British Columbia, south to Florida, New Mexico and California. July-Aug. 



22. Potamogeton obtusifolius Mert. & Koch. 

 Blunt-leaved Pondweed. Fig. 195. 



Potamogeton compressus Wahl. Fl. Suec. i : 107. 1824. 



Not L. 1753. 

 Potamogeton obtusifolius Mert. & Koch, Deutsch. Fl. 



i : 855. 1823. 



Stems usually slender, compressed, widely branch- 

 ing, especially above. Leaves linear, 2'-3' long, i"-2" 

 wide, obtuse, often mucronate, usually 3-nerved with 

 a broad midrib, sometimes 5-7-nerved, 2-glandular 

 at the base, the glands large and translucent ; stipules 

 white or scarious, many-nerved, obtuse, 6"-o/' long, 

 often as long as or longer than the internodes ; 

 peduncles numerous, i'-i|' long, slender, erect; spikes 

 3"-4" long, ovoid, 5-8-flowered; fruit obliquely obo- 

 void, about ij" long and i" thick, 3-keeled; style 

 short, blunt, nearly facial. 



In still water, Quebec to Minnesota, south to northern 

 New York and Kansas. Also in Europe. July-Aug. 



