102 CONTRIBUTIONS 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 perigynium 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): sheathe 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. anneotens. 



3. Paniculatae Kunth. 

 Heavy-headed plants, superficially resembling Echinachloa 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 MuJilenbergianae, but the long-beaked awl-shaped perigynia, 

 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. 



5. Canescentes Fries. 

 Plants pale green, somewhat glaucous. 

 A single species 17. C. canescens. 



