14 POTAMOGETONACEAE. 



Fertile flowers sessile; fruit broadly obovoid. 5. eurycarpum. 



Fertile flowers stalked; fruit fusiform. 



Heads all axillary; inflorescence branched. S. androcladum. 



Heads, or at least some of them, supra-axillary. 



Leaves, or at least the larger ones, keeled; usually 



terrestrial. S. simplex. 



Leaves not keeled; floating aquatics. 



Beak of fruit short-conical; stigma oblong. 5. minimum. 



Beak of fruit slender; stigma linear. S. angustifolium. 



Spaiganium eurycarpum Engelm. Stems stout, erect, 100-150 cm. high; 

 leaves flat, slightly keeled; staminate heads several to many; pistillate heads 

 2-4, sessile or peduncled, 15-30 mm. in diameter; fruit obtusely 4 or 5 angled, 

 7-8 mm. long, abruptly tipped in the center. Common in marshes and on 

 lake margins. 



Sparganium androcladtun (Engelm.) Morong. Stems stout, 40-100 cm. 

 high; leaves 5-12 mm. wide, dark green; inflorescence branched, the branches 

 strictly axillary, each bearing 3-7 staminate heads and usually 1 or 2 pistillate 

 heads; fruiting heads 2-2.5 cm. in diameter; fruits dull, the fusiform body 

 5-6 mm. long, the beak about 3 mm. long. Mouth of St. Joe River, Idaho. 



Sparganium simplex Huds. Stems rather stout, 30-60 cm. high; leaves 

 thin, 6-15 mm. broad, scarious-margined below; inflorescence simple; fruiting 

 heads 12-25 mm. in diameter, some of them supra-axillary; fruit fusiform, 

 somewhat shiny, the body 3-4 mm. long, tipped with a beak about as long; 

 stalk 1-2 mm. long; stigmas linear. In bogs or pond margins. 



Two forms occur in our limits, one having heads about 2 cm. in diameter 

 with very shiny fruits whose conical body is shorter than the beak; the other 

 with smaller heads, 15 mm. in diameter, and the fruits rather dull, with the 

 body abruptly tipped with a shorter beak. Perhaps neither plant is true 

 5. simplex. 



Sparganium minimum Fries. Aquatic; stems very slender, 10-40 cm. long; 

 leaves thin and grass-like, 2-4 mm. broad, floating; inflorescence simple; 

 heads sessile or nearly so, the pistillate about 1 cm. in diameter when mature; 

 nutlets smooth, ovoid, conically short-beaked, easily detached. In the lakes 

 of Spokane County and northern Idaho. 



Sparganium angustifoUum Michx. Aquatic; stems slender, 30-100 cm. 

 long; leaves very long and narrow, rather firm, 2-4 mm. wide; inflorescence 

 simple; heads sessile or the lower peduncled, the pistillate 15-20 mm. in di- 

 ameter when mature; nutlets abruptly slender-beaked, firmly attached. In 

 the lakes of northern Idaho. 



Family 11. POTAMOGETONACEAE, 



Herbs, submersed or floating in fresh or salt water ; with mostly 

 2-ranked leaves; flowers mostly small, solitary or in spikes, 

 unisexual or perfect, regular; perianth none or rarely sheath-like; 

 stamens 1-4; carpels 1-4, each 1-ovuled; fruits drupaceous or 

 membranaceous. 



Flowers perfect, in spikes. 24. Potamogeton, 15. 



Flowers unisexual, in axillary clusters. 25. Zannichellia, 16. 



