GENUS i. 



PONDWEED FAMILY. 



79 



angled face; embryo with the apex pointing slightly inside of the base. 



In Mystic Pond, Medford. Mass. Also in Europe. Summer. Apparently a mere form of the 

 preceding, or perhaps a hybrid between P. angustifolius and P. heterophyllus. 



ii. Potamogeton illinoensis Morong. 



Illinois Pondweed. Fig. 184. " 



Potamogetoii illinoensis Morong, Coult. Bot. Gaz. 

 5: 50. 1880. 



Stems stout, much branched above. Floating 

 leaves opposite, numerous, thick, 4'-5i' long, 2'-$' 

 wide, many-nerved, oval or broadly elliptic, short- 

 pointed at the apex, rounded, subcordate or nar- 

 rowed at the base; petioles i'-4 long; submerged 

 leaves numerous, 4'-8' long, i'-2' wide, 13-19- 

 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, 

 li"-2" long, i"-ii" thick, dorsally 3-keeled; style 

 short, blunt. 



In ponds, Illinois to Iowa and Minnesota. Aug. 



12. Potamogeton angustifolius Berch. & 

 Presl. Ziz's Pondweed. Fig. 185. 



P. angustifolius Berch. & Presl, Rost. 19. 1821. 



Potamogeton Zizii Roth, Enum. i: 531. 1827. 



Potamogeton luccns connecticutensis Robbins in A. 

 Gray, Man. Ed. 5, 488. 1867. 



Potamogeton angustifolius var. Methyensis A. Ben- 

 nett, Journ. Bot. 29: 151. 1891. 



Stems slender, branching. Floating leaves ellip- 

 tic, i $'-4' long, 6"-i2" wide, many-nerved; petioles 

 mostly short ; submerged leaves mostly lanceolate 

 or oblanceolate, thin, acute or cuspidate, 2'-6' 

 long, 3"-! 5" wide, 7-i7-neryed; stipules 6"-i8" 

 long, obtuse, 2-keeled ; peduncles thicker than the 

 stem, 2$'-6' long; spikes i'-2' long; fruit obliquely 

 obovoid, ii"-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 California, Florida 

 and Wyoming. Also in Europe. July-Aug. 



13. Potamogeton lucens L. Shining Pond- 

 weed. Cornstalk-weed. Fig. 186. 

 Potamogeton lucens L. Sp. PI. 126. 1/53. 



Stems 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 r -2\' long, cylindric, 

 very thick; fruit about \\" long and iJ" 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 California 

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



