MANUAL OF THE GRASSES OF THE UNITED STATES 627 



the range. P. virgatum, switch grass, and P. stipitatum, of the eastern half of the 

 United States, P. bulbosum and P. obtusum, of the Southwest, and Panicum 

 texanum in Texas furnish hay or forage. The seeds of P. sonorum Beal are used 

 for food by the Cocopa Indians. 



Axis of branchlets extending beyond the base of the uppermost spikelet as a point or bristle 



1 to 6 mm. long „ Subgenus 1. Paurochaetium. 



Axis of branchlets not extending into a bristle. (In P. geminatum and P. paludivagum the 



somewhat flattened axis is pointed but not bristle-form.) 



Basal leaves usually distinctly different from those of the culm, forming a winter rosette; 



culms at first simple, the spikelets of the primary panicle not perfecting seed, later 



usually becoming much branched, the small secondary panicles with cleistogamous 



fruitful spikelets Subgenus 2. Dichanthelium. 



Basal leaves similar to the culm leaves, not forming a winter rosette; spikelets all fertile. 



Subgenus 3. Eupanicum. 

 Subgenus 1. Paurochaetium 



Blades elongate, usually more than 15 cm. long, narrowed toward the base. 



Spikelets about 3.5 mm. long 3. P. reverchoni. 



Spikelets about 2 mm. long, or less 1. P. chapmani. 



Blades usually less than 10 cm. long, not narrowed toward the base; spikelets 2.5 to 3 mm. 

 long. 



Blades of midculm long-acuminate, usually 2 to 4 mm. wide 2. P. ramisetum. 



Blades of midculm abruptly acute, usually 4 to 7 mm. wide 4. P. firmulum. 



Subgenus 2. Dichanthelium 



Blades elongate, not more than 5 mm. wide, 20 times as long as wide; autumnal phase 

 branching from the base only (from the lower nodes in P. werneri). 



1. Depauperata. 

 Blades not elongate (or if so, more than 5 mm. wide and autumnal phase not branching from 

 base). 

 Plants branching from the base, finally forming rosettes or cushions, the foliage soft, lax. 



Blades prominently ciliate except in P. laxiflorum 2. Laxiflora. 



Plants branching from the culm nodes or rarely remaining simple. 

 Blades long, stiff; autumnal phase bushy-branched above. 



Spikelets turgid, attenuate at base; mostly pustulose-pubescent; blades conspicu- 

 ously striate, tapering from base to apex 3. Angustifolia. 



Spikelets scarcely turgid, not attenuate at base; blades tapering to both ends. 



4. Bicknelliana. 

 Blades not long and stiff (somewhat so in P. oligosanthes, P. malacon, P. commonsianum, 

 and P. equilaterale) ; not bushy-branched. 

 Plants not forming a distinct winter rosette; spikelets attenuate at base, papillose. 



14. Pedicellata. 

 Plants forming a distinct winter rosette; spikelets not attenuate at base. 



Spikelets turgid, blunt, strongly nerved (not strongly turgid in P. oligosanthes); 

 blades rarely as much as 1.5 cm. wide (sometimes 2 cm. in P. ravenelii and 

 P. xanthophysum) . 

 Sheaths or some of them, papillose-hispid (sometimes all glabrous in P. helleri) ; 

 spikelets 3 to 4 mm. long (2.7 to 3 mm. in P. wilcoxianum) . 



13. Oligosanthia. 

 Sheaths glabrous or minutely puberulent; spikelets 1.5 to 2.5 mm. long, asym- 

 metrically pyriform; culms wiry 12. Lancearia. 



Spikelets not turgid, blunt, nor strongly nerved (somewhat so in P. roanokense and 

 P. caerulescens) . 

 Ligule of conspicuous hairs, usually 3 to 5 mm. long. 



Sheaths glabrous or only the lowermost somewhat pubescent.... 7. Spreta. 



Sheaths strongly pubescent 8. Lanuginosa. 



Ligule obsolete or nearly so (manifest in P. oricola, P. tsugetorum, and P. curti- 

 folium). 

 Spikelets nearly spherical at maturity; blades glabrous, firm, cordate. Plants 



usually sparingly branching 10. Sphaerocarpa. 



Spikelets usually obovate or elliptic. 



Blades of midculm elongate, less than 1.5 cm. wide. Culms usually tall; 

 spikelets pointed, abruptly so in the velvety P. scoparium. 



15. Scoparia. 

 Blades of midculm not elongate (somewhat so in P. equilaterale). 



