- 10 - 



buds common and extremely hard. 



23 . P_j_ crispus 



23. Stem round in cross-section; leaves not toothed; 

 fruit beak 1.0 mm long or less; winter buds rare, 

 soft. 



24. Submersed leaves sessile (but not clasping) 

 (figs. 29A, 30A) , or petioled (figs. 26A, 27A, 

 28A) ; floating leaves absent or present. 



25. Submersed leaves 27-37-veined (fig. 26A) , 

 distinctly arced (fig. 26A) . 

 24 . P^ amplifolius 



25. Submersed leaves less than 27-veined, not 

 arced. 



26. Stems conspicuously black-spotted; 

 submersed leaves curly or wavy along the 

 margin (fig. 27A) ; floating leaves 

 21-35-veined. 

 25. P_j_ pulcher 



26. Stems not conspicuously black-spotted; 

 submersed leaves not curly or wavy along 

 the margin; floating leaves 

 2-29-veined . 



27. Submersed leaves with petiole 2-13 

 cm in length (fig. 28A) ; fruit 

 length 3.5-4.3 mm. 

 26 . P_^ nodosus 



27. Submersed leaves sessile (figs. 29A, 

 30A, 31, 32, 33A) (occasional leaf 

 petiolate to 4.0 cm long in 

 P. illinoensis ) ; fruit length less 

 than 3.5 mm. 



28. Submersed leaves 7-veined (often 

 with up to six additional faint 

 veins) with apex obtuse (figs. 

 29B,C) or acute (figs. 29D,E); 

 reticulate portion along midrib, 

 reddish color on drying; 

 stipules blunt (fig. 29A) ; 

 fruit plump, tawny-olive, 

 pedicelled (figs. 29G,F). 

 27. P_^ alpinus 



28. Submersed leaves 3-17-veined 

 (all prominent) with apex acute 

 or with an awl-like tip 

 (figs. 31, 33A) , lacking obvious 

 reticulate portion along the 

 midrib, not reddish color on 



