608 MISC. PUBLICATION 200, TJ. S. DEPT. OF AGRICULTURE 



Blades ascending or spreading, rarely less than 8 mm wide, usually wider; 

 plants not hirsute throughout. 

 Spikelets 3.2 to 3.3 mm long; blades firm; sheaths or some of them more 



or less hispid 92. P. scribnerianum. 



Spikelets not more than 3 mm long; blades rather thin; sheaths or 

 some of them glabrous or sparsely hispid 91. P. helleri. 



14. Pedicellata 

 Culms erect or leaning; blades thin, 5 to 9 cm long, narrowed toward the base. 



97. P. PEDICELLATUM. 



Culms decumbent; blades thick, not more than 5 cm long, not narrowed 

 toward the base 98. P. nodatum. 



15. Scoparia 

 Pubescence soft-villous or velvety. Spikelets abruptly pointed. 



99. P. SCOPARIUM. 



Pubescence when present not velvety. 



Spikelets elliptic; fruit 2 mm long 100. P. aculeatum. 



Spikelets ovate, that is, broadest below the middle; fruit 2 mm long or less. 

 Sheaths or some of them hispid, rarely glabrous; autumnal phase with 



crowded branchlets 101. P. scabriusctjlum. 



Sheaths glabrous; autumnal phase sparingly branching. 



102. P. CRYPTANTHUM. 



16. Commutata 



Plants glaucous, glabrous. Basal blades conspicuously ciliate; vernal culms 



usually solitary 105. P. mutabile. 



Plants not glaucous. 



Blades nearly linear, that is, with parallel margins. First glume about half 



as long as the spikelet 107. P. equilaterale. 



Blades lanceolate. 



Culms crisp-puberulent; blades usually rigid, symmetrical, rarely more than 



10 mm wide; spikelets about 2.5 mm long 103. P. ashei. 



Culms glabrous or softly puberulent; blades firm or lax; spikelets 2.7 to 3.2 

 mm long. 

 Culms erect, or autumnal phase leaning; blades symmetrical, broadly 



cordate 104. P. commutattjm. 



Culms decumbent; blades usually asymmetrical and falcate, narrowed to 

 the scarcely cordate base 106. P. joorii. 



1 7. Latifolia 

 Sheaths strongly papillose-hispid, at least the lower and those of the branches. 



108. P. CLANDESTINTJM. 



Sheaths glabrous or softly villous. 



Nodes glabrous; spikelets 3.4 to 3.7 mm long 109. P. latifolium. 



Nodes bearded; spikelets 4 to 4.5 mm long 110. P. boscii. 



Subgenus 3. Ewpanicum 

 la. Plants annual. 



Inflorescence consisting of several more or less secund spikelike racemes. Fruit 



transversely rugose 3. Fascictjlata. 



Inflorescence a more or less diffuse panicle. 



Spikelets tuberculate 12. Verrucosa. 



Spikelets not tuberculate. 



First glume not more than one-fourth the length of the spikelet, truncate 



or triangular-tipped 4. Dichotomiflora. 



First glume usually as much as half the length of the spikelet, acute or 



acuminate 5. Capillaria. 



lb. Plants perennial. 



2a. Spikelets short-pediceled along one side of the rachises, forming spikelike 

 racemes (compare Agrostoidia with 1-sided but not spikelike panicle 

 branches) . 

 First glume nearly equaling the sterile lemma. 



Racemes spreading; fruit not more than one-third the length of the 



spikelet 16. Gymnocarpa. 



Racemes appressed; fruit nearly as long as the spikelet 14. Obtusa. 



