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Potamogeton (Pondweed) 



Plants of fresh or saline water; growing from rhizomes 

 or winter buds; leaves alternate, variable, with a 

 characteristic mid-vein; floating leaves present in many 

 species; flowers borne in spikes which may or may not rise 

 above the water's surface; fruits drupaceous. Many hybrids 

 occur, particularly between the broad-leaved species. 



Key to Species 



Plants with stipules adnate to leaf sheaths (figs. 2D, 3B , 

 6B) . 



2. Stipules adnate to leaf for 10 mm or more (figs. 2D, 

 3B) ; floating leaves absent; fruit usually without a 

 lateral keel, embryo indistinctly coiled (figs. 3E, 

 5C) . 



3. Leaves 3-8 mm wide, stiffish, 2-ranked, lobed at 

 junction with stipule (fig. 2D); leaves usually 

 with fine serrations, seen under magnification (fig. 

 2C) . 

 1 . P_^ robbinsii 



3. Leaves 0.2-2.0 mm wide, lax, not distinctly 

 2-ranked, nor lobed at base; leaves without 

 serrations. 



4. Leaves acute (fig. 3D), apiculate on young 

 plants (fig. 3C) ; fruits beaked (fig. 3E) . 

 2 . P_^ pectinatus 



4. Leaves blunt (fig. 5H) , obtuse (fig. 4E) , 

 notched (figs. 4C,D, 5G) or rarely apiculate 

 (fig. 4F) . 



5. Plants tall, 3-10 dm long; stipules on 

 lower portion of stem loose and inflated 

 (fig. 43), disintegrating early (fig. 4A) ; 

 leaves 0.5-2.0 mm wide 



3 . P^ f iliformis 



var . occidental is 



5. Plants short, 1-3 dm long; stipules on the 

 lower portion of the stem usually tightly 

 clasping, not disintegrating (figs. 5D,E); 

 leaves 0.2-0.8 mm wide 



4 . P_^ f iliformis 



var . alpinus 



2. Stipules adnate to leaf for a distance of less than 10.0 



mm; floating leaves absent or present; fruit with 



obvious lateral keel and embryo distinctly coiled (figs. 

 6C, 7C,D, 8D) . 



