30 POACEAE 



Spikelets 2-many-flowered. 



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



bent. Tribe 7. Aveneae. 



^jemma 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 raclus-internodes with a translucent cup-shaped 



appendage. 1- Schizachyrium. 



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

 Rachis-lnternodes and pedicels silicate, 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. Sorghastrum. 



Pedicellate spikelets present and usually staminate. 5. Holcus. 



Tribe 2. ZOYSIEAE. 

 Only one genus represented. 6. Pleur.^phis. 



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. Paspalxj'M. 



Empty glumes 3. 



Empty glumes not awned. 



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

 proximate. 8. SYNTHERISMA. 

 Spikelets in panicles or panicled racemes. 



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



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



10. PAN'icxnw. 

 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. Phal.\ris. 



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. Lycurus. 

 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), projectmg from the apex ol 

 the nearly closed glumes. 



Racliilla of the spikelets articulated above the empty glumes, wliich are there- 

 fore persistent. 23. Phleum. 

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

 spikelets fallinj? off entire. 24. Alopecurus. 

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



25. Phippsia. 



