Scirpus Cyperaceae 193 



Culms obtusely 3-angled with concave sides; leaves nodulose; involucral bract 

 blunt; achenes trigonous, smooth; bristles much longer than the achene. 



5. S. Torreyi. 



Involucral bract usually shorter than the inflorescence or merely equaling it. 



Culms rather soft; inflorescence lax, usually drooping; spikelets many, ovoid, 

 on long, drooping pedicels; achenes obovoid, 1.5-2 mm long, plano-convex; 

 bristles usually longer than the achene 6. S. validus. 



Culms rather stiff and firm; inflorescence erect, the spikelets and pedicels 

 erect or ascending, compact; spikelets subcylindric ; achenes obovoid, in 

 my specimens ranging from 2.3-3 mm long, unequally biconvex; bristles 

 about equaling the achene or slightly shorter 7. S. aciitus. 



Involucral bracts 2 or more. 



Bristles retrorsely barbed or lacking. 



Spikelets large, usually 1.5-4 cm long; achenes trigonous, about 4 mm long 



8. S. fluviatilis. 



Spikelets small, generally less than 1 cm long. 



Bristles scarcely longer than the achene, usually slightly shorter, rudimentary, 



or lacking; scales of mature spikelets with a light reddish background 



suffused with a lead color; achenes colorless, obovoid-oblong, trigonous, 



about 1 mm long. 



Bristles present, about equaling the achene; lower sheaths nodulose; leaves 



usually 10-18 mm wide; major glomerules usually more than 7 mm in 



diameter 9. S. atrovirens. 



Bristles lacking or rudimentary; lower sheaths not nodulose or only faintly so; 

 leaves usually less than 10 mm wide; major glomerules usually not over 

 7 mm in diameter; rays of inflorescences usually longer than in the 



preceding; glomerules usually not so crowded 



9a. S. atrovirens var. georgianus. 



Bristles twice the length of the achene; scales of spikelets rufous brown with 



green midribs; principal leaves usually 6-8 mm wide 10. S. polyphyllus. 



Bristles smooth or with a few ascending barbs, curly. 



Rays and pedicels smooth or somewhat scabrous below the involucels, not con- 

 spicuously striate, both usually drooping; scales reddish brown with strong, 

 green midribs prolonged into sharp, short, spreading points; achenes about 

 1 mm long, Fawn Color (Ridgway Standard) ; bristles weak, about twice the 



length of the achene, included 11. S. lineatus. 



Rays (except the primary ones) and pedicels strongly upwardly scabrous, con- 

 spicuously striate, at least the principal rays inclined to be erect; scales of 

 spikelets reddish, sometimes suffused with greenish black, the midrib not 

 green, somewhat obtuse at the apex; achenes about 0.8 mm or less in length, 

 colorless; bristles curled and much exserted beyond the scales. 

 Spikelets mostly sessile, in glomerules of 3-15. 



Involucres and involucels reddish brown; scales reddish brown. 



Spikelets ovoid, 3-6 mm long 12. S. cyperinus. 



Spikelets cylindric, 7-10 mm long 12a. S. cyperinus f. Andrewsii. 



Involucres and involucels drab with a blackish base. 



Rays of normal length, the glomerules distinct, scales brownish, suffused with 



greenish black 12b. S. cyperinus var. pelius. 



Rays abbreviated, the glomerules crowded into dense, irregular masses. 



12c. S. cyperinus var. pelius f. condensatus. 



Spikelets mostly pedicellate, usually arranged in small clusters with the central 

 one sessile and the remainder on pedicels of different lengths. 



Involucels red brown or terra cotta 13. S. Eriophorum. 



Involucels dull brown, not reddish 14. S. pedicellatus. 



Involucels black. (See excluded species no. 88, p. 10.'! 1.) S. atrocinctus. 



