102 CONTRIBUTIOlSrS FROM THE NATIONAL, HERBARIUM. 



Spikes densely flowered, much coarser; perigynia not spongy below the middle 

 (except in C. conjuncta). 

 Leaves less than 4.5 mm. broad; sheaths tight, often thickened at the mouth (sheaths 

 loose in C aggregata). 



Scales tinged with reddish purple; perigynia 4-6.5 mm. long 4. C. muricata. 



Scales greenish or nearly hyaline; perigynia shorter. 



Heads 25-40 mm. long; lower spikes distinct (except in C. aggregata). 

 Sheaths tight; beak of perigynivun half as long as the body. 



5. C. muhlenbergii. 



Sheaths loose; beak of perigynium equaling the body 9. C. aggregata. 



Heads 10-20 mm. long; lower spikes not distinct. 



Scale body equaling the broadly ovate perigynium 6. C. mesochorea. 



Scale body much shorter than the perigynium, 

 Perigynium narrow at the base; leaves 2-4.5 mm. wide. 



7. C. cephalophora. 

 Perigynium broad at the base, cordate or nearly so; leaves 0.7-2 mm. wide. 



8. C. leavenworthii. 



Leaves more than 4.5 mm. broad (usually narrower in C aggregata); sheaths loose, 



membranaceous. ' 



Culms sharply triangular, not winged; perigynium not spongy below the middle. 



Lower spikes not separate; only the broadest leaves, if any, over 4.25 mm. 



broad 9. C. aggregata. 



Lower spikes widely separate; leaves mostly 5 mm. broad or more. 



10. C. sparganioides. 

 Culms narrowly winged; perigynium slightly spongy below the middle. 



11. C. conjuncta. 



2. Multiflorae Kunth. 



Represented by only 2 species in our region. Conspicuous by its many-flowered, 

 often somewhat compound heads, dense, dull brown or yellow-brown spikes, and 

 numerous setaceous bracts. 



Leaves longer than the culm; beak of perigynium equaling the body. 



12. C. vulpinoidea. 

 Leaves shorter than the culm; beak of perigynium much shorter than the body. 



13. C. annectens. 



3. Paniculatae Kunth. 



Heavy-headed plants, superficially resembling Echinochloa crusgalli. 

 A single species 14. C. decomposita. 



4. Stenorhynchae Holm. 



Two closely allied species are found here, somewhat resembling the coarser- 

 headed species of the Muhlenbergianae, but the long-beaked awl-shaped perigjTiia, 

 with very corky bases, are very distinct from any in that group. 



Sheaths wrinkled, loose at the mouth 15. C. stipata. 



Sheaths not wrinkled, tight at the mouth 16. C. laevivaginata. 



6. Canescentes Fries. 

 Plants pale green, somewhat glaucous. 

 A single species 17. C. canescens. 



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