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



P. bulbosum and P. obtusum, of the Southwest, and Panicum texanum 

 in Texas, furnish hay or forage. The seeds of P. sonorum Beal, of 

 Northwest Mexico, are used for food by the Cocopa Indians. 



Axis of branchlets extending beyond the base of the uppermost rpikelet 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. paludi- 

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

 Basal leaves usually distinctly different from those of the culm, forming a win- 

 ter rosette; culms at first simple, the spikelets of the primary panicle not 

 perfecting seed, later usually becoming much branched, the small secon- 

 dary 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 3 mm wide. 



2. P. RAMISETUM. 



Blades of midculm abruptly acute, usually 4 to 6 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 



conspicuously 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 wade (sometimes 2 cm 



in P. ravenellii 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. wil- 



coxianum) 13. Oligosanthia. 



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



asymmetrically 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. curtifolium) . 



