30 POACEAE 



Spikelets 2-many-flowered. 



Lemma usually shorter than the empty glumes; the awn dorsal and usually 



bent. Tribe 7. AVENEAE. 



Lemma usually longer than the empty glumes; the awn terminal and straight 



(rarely dorsal in Bromus) or none. Tribe 9. FESTUCEAE. 



Spikelets in two rows, sessile or nearly so. 



Spikelets on one side of the continuous axis, forming one-sided spikes. 



Tribe 8. CHLORIDEAE. 



Spikelets alternately on opposite sides of the axis, which is often articulated. 



Tribe 10. HORDEAE. 



TRIBE 1. ANDROPOGONEAE. 

 Racemes singly disposed; apex of the rachis-internodes with a translucent cup-shaped 



appendage. 1. SCHIZACHYRIUM. 



Racemes disposed in pairs or more; apex of the rachis-internodes not appendaged. 

 Rachis-internodes and pedicels sulcate, the median portion translucent, the margins 



thickened. 2. AMPHILOPHIS. 



Rachis-internodes not sulcate. 



Some or all of the racemes sessile. 3. ANDROPOGON. 



All of the racemes more or less peduncled. 



Pedicellate spikelets wanting. 4. SORGHASTRTJM. 



Pedicellate spikelets present and usually staminate. 5. HOLCUS. 



TRIBE 2. ZOYSIEAE. 

 Only one genus represented. 6. PLEURAPHIS. 



TRIBE 3. PANICEAE. 

 Spikelets naked, not involucrate. 

 Empty glumes 2. 



Rachis produced beyond the upper spikelet; spikelets narrow. 



39. SPARTINA. 

 Rachis not so produced ; spikelets globose or obovoid. 



Spikelets obovoid, turgid. 40. BECKMANNIA. 



Spikelets plano-convex. 7. PASPAL.UM. 



Empty glumes 3. 



Empty glumes not awned. 



Spikelets in very slender 1-sided racemes, which are usually whorled or ap- 



proximate. 8. SYNTHERISMA. 



Spikelets in panicles or panicled racemes. 



Spikelets lanceolate, acuminate, long-hairy. 9. VALLOTA. 



the 



Spikelets orbicular or lanceolate, if the latter, then glabrous. 



10. PANICUM. 



Empty glumes awned or awn-pointed. 11. ECHINOCHLOA. 



Spikelets involucrate. 



Involucre of bristles. 12. CHAETOCHLOA. 



Involucre of two spine-bearing valves. 13. CENCHRUS. 



TRIBE 4. ORYZEAE. 

 Spikelets perfect; empty glumes wanting or rarely rudimentary. 14. HOMALOCENCHRUS. 



TRIBE 5. PHALARIDEAE. 



Third and fourth glumes empty, awnless. 15. PHALARIS. 



Third and fourth glumes enclosing staminate flowers. 16. TORRESIA. 



TRIBE 6. AGROSTIDEAE. 

 Lemma indurate when mature and very closely embracing the grain, or at least firmer 



than the empty glumes. 

 Spikelets all perfect, not in pairs. 



Lemma 3-awned. 17. ARISTIDA. 



Lemma 1 -awned or awnless. 



Awn twisted and bent. 18. STIPA. 



Awn not twisted. 



Lemma broad; awn deciduous. 



Inflorescence paniculate or racemiform. 19. ORYZOPSIS. 



Inflorescence dichotomous. 20. ERIOCOMA. 



Lemma narrow, glabrous or with short, appressed hairs; awn, if any, per- 



sistent. 21. MUHLENBERGIA. 



Spikelets in pairs, one perfect and the other staminate or sterile, in a spike-like pan- 



icle. 22. LYCTJRUS. 



Lemma usually hyaline or membranaceous at maturity, at least more delicate than the 



empty glumes. 

 Stigma sub-plumose (i. e., with short hairs all around), projecting from the apex of 



the nearly closed glumes. 

 Inflorescence spike-like. 



Rachilla of the spikelets articulated above the empty glumes, which are there- 



fore persistent. 23. PHLEUM. 



Rachilla of the spikelets articulated below the empty glumes, hence the 



spikelets falling off entire. 24. ALOPECURUS. 



Inflorescence an open small panicle; dwarf arctic-alpine plant. 



25. PHIPPSIA. 



