- 9 - 



10. Floating leaves present on at least some plants 

 in population (Figs. 2lA, 22E). 



20. Floating leaves 0.6-1.5 cm long, 5-9-veined: 

 submersed leaves thin and transparent; 

 fruit less than 2.5 cm long. 



21. Submersed leaves 0.1-1.0 mm wide; 

 floating leaves 5-9-veined, often 

 obovate (fig. 21A) ; winter buds common 

 (fig. 21E); fruit compressed with 

 distinct dorsal keel and recurved beak 

 (fig. 21B) ; no fruit on plants with 

 only submersed leaves. 

 19 . P_^ vaseyi 



21. Submersed leaves 0.4-1.0 mm wide; 

 floating leaves 5-7-veined, usually 

 spatulate (fig. 22E) ; winter buds 

 usually absent; fruit slightly 

 compressed with strongly rounded back 

 (fig. 22D) , (fruit very similar to P . 

 pusillus ) ; winter buds occasionally 

 found; fruit only on plants with 

 submersed leaves, but plants with 

 floating leaves may bear flowers. 

 20. P_^ lateralis 



20. Floating leaves, 1.5-12.0 cm long, 

 7-37-veined; submersed leaves thick and 

 phyllodia-like (or stem-like) (fig. 23A) ; 

 fruit 2.5-3.5 cm long. 



22. Submersed (phyllodial) leaves 0.8-2.0 mm 

 wide; floating leaf blades 2.5-6.0 cm 

 wide, 13-37 veins, usually heart-shaped 

 at base (fig. 23A) , (floating leaves in 

 strong currents lack heart-shaped 

 bases); petiole pale at summit; fruits 

 mostly 3.5-5.0 mm long, keels obscure 

 (fig. 23B) . 

 21. P_^ natans 



22. Submersed (phyllodial) leaves 0.3-1.0 mm 

 wide; floating leaf blades 1.0-3.0 cm 

 wide, rounded or wedge-shaped at base 

 (fig. 24A) ; petiole not pale at 

 summit; fruits mostly 2.5-3.5 mm long, 

 keels prominent (fig. 24B) . 

 22 . P_^ oakesianus 



Submersed leaves non-linear, without parallel margins 

 (figs. 26A, 30A) , 10.0 mm-75.0 mm wide. 



23. Stem flattened; margins of leaves conspicuously 

 toothed (fig. 258); stipules slightly fused to base 

 of leaf; fruit beak 2-3 mm long (fig. 25C); winter 



