NAIADACEAE. 



ii. Potamogeton Illinoensis Morong. 

 Illinois Pondweed. (Fig. 152.) 



Potamogeton Illinoensis Morong, Coult. Bot. Gaz. 



5: 50. 1880. 



Stem stout, much branched above. Floating 

 leaves opposite, numerous, thick, 4 / -5>^ / long, 

 2 / -3^ / wide, many-nerved, oval or broadl}- ellip- 

 tic, short-pointed at the apex, rounded, subcor- 

 date or narrowed at the base; petioles \'-\ f long; 

 submerged leaves numerous, 4 / -8 / long, i / -2 / 

 wide, 13-ig-nerved, acuminate or the uppermost 

 acute, mostly tapering at the base into a short 

 broad flat petiole, rarely reduced to phyllodes; 

 stipules 2'-$' long, obtuse, strongly 2-carinate; 

 peduncles 2' '-4' long; spikes i'-2' long; fruit 

 roundish or obovoid, i%"-2" long, i // -i^ // 

 thick, dorsally 3-keeled ; style short, blunt. 



In ponds, Illinois to Iowa and Minnesota. Aug. 



12. Potamogeton Zizii Roth. Ziz's Pondweed. (Fig. 153.) 



Potamogeton ansftislifolius Berch. & Presl, Rost. 



19. "iS2i. Not DC. 1805. 

 Potamoytton Zizii Roth, Enutn. i: 531. 1827. 



Stems slender, branching. Floating leaves 

 elliptic, ij'-4' long, 6 // -i2 // wide, uiany- 

 nervcd ; petioles mostly short ; submerged 

 leaves mostly lanceolate or oblanceolate, thin, 

 acute or cuspidate, 2'-6' long, 3 // -i5 // wide, 

 7-i7-nerved ; stipules 6"-i8" long, obtuse, 

 2-keeled ; peduncles thicker than the stem, 

 2j'-6' long; spikes i / -2 / long; fruit obliquely 

 obovoid, i%"-2" long, about i" thick, the face 

 dorsally 3-keeled; style short, blunt, facial; apex 

 of the embryo pointing directly to the base. 



In lakes and streams, Quebec to Montana, south to 

 Florida and Wyoming. Also in Europe. July-Aug. 



Potamogeton Zizii Methyensis (A. Benn.) Morong. 

 J\>t<ii<i^t't(ni aiigttstifoliitsvar. Mfthvensis A. Ben- 



nett. 'Britten's Jourh. Bot. 29: 151. "1891. 



Middle leaves narrow; upper leaves oval; stipules 

 long: fruit small. Methy Lake. Canada. 



13. Potamogeton lucens L,. Shining 

 Pondweed. (Fig. 154.) 



Potamogeton lucens L. Sp. PI. 126. 1753. 



Stem thick, branching below and often with 

 masses of short leafy branches at the summit. 

 Leaves all submerged, elliptic, lanceolate or the 

 uppermost oval, shining, acute or acuminate and 

 cuspidate, or rounded at both ends and merely 

 mucronulate, sessile or short-petioled, 2> / -8 / 

 long, 8 // -2o // wide, the tips often serrulate ; 

 stipules i '-3' long, 2-carinate, sometimes very 

 broad ; peduncles 3 '-6' long ; spikes 2 / -2^ / 

 long, cyliudric, very thick; fruit about \W 

 long and i#" thick, roundish, the face usually 

 with a slight inward curve at the base ; apex 

 of the embryo pointing transversely inward. 



In ponds, Nova Scotia to Florida, west to Califor- 

 nia and Mexico. Local. Also in Europe. Sept.-Oct. 

 PoUmogeton lucens Connecticutensis Robbins in A. Gray, Man. Ed. 5, 488. 1867. 

 Hi Hi-\iK.u>: h-avi-s acuminate: fruit larger than that of the type (about 2" long) distinctly 

 3-cannatt and with a facial style. Saltonstairs I'ond, Conn., and White Plains, N. V. 



