FLORA OF THE DISTRICT OF COLUMBIA. 93 



1. CYPERUS L. 



Plants annual, tufted. 

 Achenes lenticular; stigmas 2. Rachilla narrow, continuous, the scales and achenes 

 deciduous; culms mostly less than 30 cm. tall. 



Scale tips not appressed; spikelets not over 2 mm. wide 1. C. microdontus. 



Scale tips appressed ; spikelets 2.5-3 mm. wide. 



Scales reddish-tinged; achenes dull brown, 1.2 mm. long 2. C. diandrus. 



Scales yellowish; achenes shining black, less than 1 mm. long. 3. C. flavescens. 

 Achenes 3-sided; stigmas 3. 



Spikelets crowded on a very short axis, forming flabellate or round heads, these 

 solitary or in short-rayed umbels. 



Scale tips acuminate, recurved 4. C. aristatus. 



Scale tips blunt, not recurved 5. C. fuscus. 



Spikelets pectinate on an elongate axis; umbel usually many-rayed. 

 Spikes 2-3 times as long as broad; rachilla continuous, the scales and achenes 



deciduous 6. C. erythrorhizos. 



Spikes about as broad as long; rachilla disarticulating, the achenes attached. 



7. C. speciosus. 

 Plants perennial, hard and cormlike at base or stoloniferous. 

 Rachilla persistent after the fall of the scales and achenes. 

 Spikelets minute, not over 4 mm. long, nearly as broad, ovate, crowded in dense 



heads, these in long-rayed umbels 8. C. pseudovegetus. 



Spikelets usually 10 mm. long or more, linear. 

 Plants not stoloniferous; culms cormlike at base; spikelets in subglobose heads, 



solitary or few 9. C. filiculmis. 



Plants very smooth, almost waxy, stoloniferous, the stolons bearing hard tubers ; 

 spikelets loosely pectinate. 



Scales reddish chestnut; spikelets about 1.5 mm. wide 10. C. rotundus. 



Scales stramineous; spikelets about 1 mm. wide 11. C. esculentus. 



Rachilla falling from the axis of the spike, either entire or disarticulating. 

 Spikelets strongly flattened. Umbels large, one-quarter to one-third the entire 



height of the plant 12. C. strigosus. 



Spikelets subterete or but slightly flattened. 



Spikelets radiate, in dense subglobose or short-cylindric heads, few-flowered, 

 bluntish. 



Heads globose or subglobose 13. C. ovularis. 



Heads short-cylindric 14. C. torreyi. 



Spikelets reflexed, in cylindric or turbinate heads, sharp-pointed. 

 Heads turbinate, the spikelets sharply reflexed; culms scabrous below the 

 umbel. 

 Basal leaves nearly as long as the culm; heads usually 2.5-3 cm. long, 



the base attenuate ' 15. C. dipsaciformis. 



Basal leaves much shorter than the culm; heads not over 2 cm. long, short- 



turbinate 16. C. retrofractus. 



Heads subcylindric; culms smooth. 



Spikelets crowded 17. C. lancastriensis. 



Spikelets not crowded 18. C. refractus. 



1. Cyperus microdontus Torr. 



Wet sand and alluvium near streams; Bladensburg, Kenilworth, Hyattsville, and 

 eastward; frequent. Aug.-Oct. Atlantic Coastal Plain, (C. nuttallii of Ward's 

 Flora.) 



2. Cyperus diandrus Torr. 



Margins of ponds and streams; Chevy Chase Lake, Eastern Branch, and southward; 

 frequent. July-Sept. Eastern and middle states. (('. diandrus rasfaneus of 

 Ward's Flora.) 



