8 



3. Plants with long linear leaves over 30 cm (fig. 6A); in fast 

 moving freshwater. 



2b. S. suhulata var. gracillima 



Leaves differentiated into petiole and blade (fig. 8A) or if blade- 

 less, then leaves terete and quill-like (fig. 7A, B), occasionally 

 submersed leaves in populations ribbon-like (fig. 13A), usually 

 greater than 3 mm wide. 



4. Stamens with pubescent filaments (fig. 7E); leaves not sagit- 

 tate (rarely in S. rigida). 



5. Emersed and submersed leaves terete and quill-like (fig. 7A, 

 B). 



3. S. teres 



5. Emersed and submersed leaves flattened (figs. 8, 9, 11, 13). 

 6. Flower and fruit heads pedicelled (fig. 8A); scape straight, 

 upright (fig. 8B); leaves linear-lanceolate phyllodia (fig. 

 8B, C) or with narrow to broad lanceolate tapering blades; 

 achenes rarely forming (in New England), 1.5-2.0 mm 

 long, with small beak, 0.1-0.3 mm long. 



4. S. graminea 



6. Flower and fruit heads sessile or nearly so (fig. 9A); scape 

 weak, often bent (fig. 9A); leaves erect, lanceolate (fig. 9C) 

 to ovate (fig. 9B), occasionally with basal lobes (fig. 9D); 

 achenes regularly formed, 2.5-4.0 mm long, with erect or 

 arching beak 1.0-1.5 mm long (fig. 9F). 



5. S. rigida 



4. Stamens with glabrous filaments; leaves mostly sagittate (fig. 

 lOA). 

 7. Achenes with beak horizontal (fig. lOE). 



6. S. latifolia 



7. Achenes with beak erect (fig. 12C, 14D). 



8. Achenes 2.0-2.6 mm long, with tiny erect beak, 0.2-0.4 mm 

 long (fig. 12C); submersed plants forming broad, ribbon- 

 like leaves (fig. 13A) and/or floating lanceolate or sagit- 

 tate leaves (fig. 13A, B); emersed plants usually with 

 recurved petioles (fig. 12A). 



7. S. cuneata 



8. Achenes 3.6-4.5 mm long with erect or oblique beak 1.5-2.0 

 mm long (fig. 14D); plants always emersed, petioles 

 ascending (fig. 14A, B). 

 8. S. engelmanniana 



