MANUAL OF THE GRASSES OF THE UNITED STATES 393 



Spikelets short-pediceled and appressed along the main panicle- 

 branches. 



Spikelets about 4 mm long, purplish 13. S. curtissii. 



Spikelets about 3 mm long, pale 29. S. tharpii. 



Spikelets not appressed, the branchlets and pedicels somewhat 

 spreading. 



Blades terete 14. S. teretifolius. 



Blades flat or folded. 



Glumes about equal, as long as the lemma. 



15. S. FLORIDANUS. 



Glumes unequal. 



Blades elongate 12. S. heterolepis. 



Blades mostly less than half as long as culm. 



11. S. INTERRUPTED 



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



5a. Lower panicle branches in distinct whorls, the mature panicle pyram- 

 idal; spikelets about 1 mm long 18. S. ARGUTUS. 



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

 in S. domingensis) ; 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 25. S. buckleti. 



6b. Basal sheaths not compressed-keeled. 



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

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



24. 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 spikelets loosely arranged 21. 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 20. S. cryptandrus. 



Base of plant a cluster of knotty rhizomes. Culms erect, 

 slender, mostly less than 30 cm tall; blades short, 



involute, spreading 22. S. nealleyi. 



Panicle compact, spikelike, usually exserted. 



23. S. CONTRACTUS. 



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



Pedicels elongate, capillary 28. S. texanus. 



Pedicels short. 



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



crowded; blades mostly involute 26. 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. 



19. S. DOMINGENSIS. 



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

 cm 27. S. WRIGHTII. 



1. Sporobolus ramulosus (H. B. K.) Kunth. Red dropseed. 

 (Fig. 813.) Annual; culms spreading, branching at the lower nodes, 

 10 to 20 cm tall; blades flat, lax, mostly 1 to 3 cm long, 1 mm wide 

 or less; panicle oblong, 2 to 5 cm long, the branches ascending, the 

 pedicels short, stiff, appressed along the main branches; spikelets 

 about 1 mm long; glumes broad, obtuse, about equal, half as long as 

 the spikelet; lemma rather turgid, acutish. o Open dry ground, 

 Colorado, New Mexico, Arizona, south to Guatemala. 



2. Sporobolus microspermus (Lag.) Hitchc. Sixweeks dropseed. 

 (Fig. 814.) Annual; culms erect or spreading, branching below, 10 to 

 30 cm tall; blades flat, lax, mostly less than 10 cm long, 1 to 2 mm wide; 

 panicle oblong, open, half or two-thirds as long as the entire culm, 

 the slender pedicels spreading, club-shaped below the spikelets; spike- 



