414 MISC. PUBLICATION 200, U. S. DEPT. OF AGRICULTURE 



Rhizomes short; leaves not numerous nor crowded nor involute; panicle narrow but 



loose 6. S. MACER. 



2b. Plants without creeping rhizomes. 



3a. Glumes nearly equal, much shorter than the lemma. Panicle narrow or spikelike. 



Panicle branches short and appressed, the panicle spikelike 8. S. poiretii. 



Panicle branches slender, ascending, the panicle scarcely spikelike.— 9. S. indicus. 

 3b. Glumes unequal or if equal as long as the spikelet. 



4a. Spikelets mostly 3 to 7 mm. long. Plants usually less than 1 m. tall. 



Second glume shorter than the lemma; panicle contracted, more or less included in 

 the sheath. 



Lemma glabrous, the palea not exceeding it 5. S. asper. 



Lemma pubescent, the palea acuminate, exceeding it 7. S. clandestinus. 



Second glume about as long as the lemma; panicle open (contracted in S. pur- 

 purascens), not included. 

 Branches of the narrow panicle in distinct whorls, usually less than 4 cm. long. 

 Branches 2 to 3 cm. long, somewhat distant, more or less spreading, the panicle 



open 17. S. junceus. 



Branches 1 to 2 cm. long, ascending or appressed, overlapping, the panicle 



contracted _ 18. S. purpurascens. 



Branches of the open panicle not in distinct whorls, usually more than 4 cm. long. 

 Spikelets short-pediceled and appressed along the main panicle branches. 



Spikelets about 4 mm. long, purplish 14. S. curtissii. 



Spikelets about 3 mm. long, pale 30. S. tharpii. 



Spikelets not appressed, the branches and pedicels somewhat spreading. 



Blades terete 15. S. teretifolius. 



Blades flat or folded. 



Glumes about equal, as long as the lemma 16. S. floridanus. 



Glumes unequal. 



Panicles 30 to 50 cm. long, purple; culms mostly more than 1 m. tall. 



13. S. SILVEANUS. 

 Panicles 10 to 20 cm. long, gray or lead-colored; culms 30 to 70 cm. tall. 



Blades elongate 12. S. heterolepis. 



Blades mostly less than half as long as culm.... 11. S. interruptus. 

 4b. Spikelets 1 to 2.5 mm. long (sometimes 3 mm. in S. giganteus). 



5a. Lower panicle branches in distinct whorls, the mature panicle pyramidal; 



spikelets about 1 mm. long 19. S. pyramidatus. 



5b. Lower panicle branches not in distinct whorls (occasionally whorled in S. 

 doming ensis); spikelets 1.5 to 2.5 mm. long. 

 6a. Basal sheaths compressed-keeled. Panicle branches few, widely spreading, 

 naked for about one-third their length; spikelets 1.5 mm. long. 



26. S. BUCKLEYI. 

 6b. Basal sheaths not compressed-keeled. 



7a. Sheaths with a conspicuous tuft of white hairs at summit. 

 Culms robust, 1 to 2 m. tall; spikelets 2.5 to 3 mm. long. 



25. S. GIGANTEUS. 



Culms more slender, mostly less than 1 m. tall; spikelets 2 to 2.5 mm. long. 

 Panicle open, often large, the branches and branchlets flexuous, the spike- 

 lets loosely arranged 22. S. flexuosus. 



Panicle open or compact, if open the spikelets crowded on the branchlets. 

 Panicle, or the exserted portion, somewhat open, the branches naked 

 below (sometimes entirely enclosed). 



Base of plant a close tuft 21. S. cryptandrus. 



Base of plant a duster of knotty rhizomes. Culms erect, slender, 

 mostly less than 30 cm. tall; blades short, involute, spreading. 



23. S. NEALLEYI. 



Panicle compact, spikelike, usually exserted 24. S. contractus. 



7b. Sheaths naked or nearly so at the summit. 



Pedicels elongate, capillary.... 29. S. texanus. 



Pedicels short. 



Panicle 1 to 2 times as long as wide, loose, the branches not crowded; 



blades mostly involute 27. S. airoides. 



Panicle more than 3 times as long as wide, relatively dense; blades mostly 

 flat. 

 Panicle not more than 20 cm. long, usually smaller. 



20. S. domingensis. 

 Panicle commonly 50 cm. long, rarely as small as 25 or 30 cm. 



28. S. WRIGHTII. 



