8 MISC. PUBLICATION 243, U.S. DEPT. OF AGRICULTURE 
TRIBE 3. HORDEAE 
Spikelets 1- to several-flowered, sessile on opposite sides of a jointed 
or continuous axis forming symmetrical spikes. 
Spikelets solitary at each node of the continuous rachis___._26. Lotrum (p. 61). 
Spikelets in threes at each node of the articulate rachis_.25. Horprum (p. 61). 
TRIBE 4. AVENEAE 
Spikelets 2- to several-flowered in open or contracted panicles, or 
rarely in racemes; glumes usually as long as or longer than the first 
lemma, commonly longer than all the florets; lemmas usually awned 
from the back or from between the teeth of a bifid apex, the awn 
usually bent, often twisted, the callus and rachilla joints usually 
villous. 
Articulation below the spikelet. 
Second glume narrowed above; lemma of second floret awned on the back, the 
awn hooked plus 2. 2a see ares eter ils, leet Be ee 32. Hotcus (p. 68). 
Second glume broadened above; lemmas awnless__28. SPHENOPHOLIS (p. 62). 
Articulation above the glumes and between the florets. 
Plants annual. 
Spikelets more thanei-cm long S22 2==522=52=.. ee ee ee 31. AVENA (p. 68). 
Spikelets lessithanyo aamis] om eee e eee 27. KOELERIA (p. 62). 
Plants perennial. 
Awn from between the teeth of the lemma, flat, twisted below. 
33. DANTHONIA (p. 70). 
Awn dorsal, terete, straight or twisted. 
Panicle dense, spikelike; lemma acute__________- 29. TRISETUM (p. 64). 
Panicle open, lemmas truncate, erose-dentate _80. DEScHAMPsIA (p. 64). 
TRIBE 5. AGROSTIDEAE 
Spikelets 1-flowered, usually perfect, in open, contracted, or spike- 
like panicles, but not in true spikes nor in one-sided racemes. 
Lemmas awnea. 
Awn trifid (lateral awns rarely minute) _.____-.___----- 40. ARISTIDA (p. 87). 
Awn simple. 
Glumes awned; panicle contracted____-_.._--_-_- 36. POLYPOGON (p. 75). 
Glumes awnless; panicle open or narrow, not contracted. 
Awn from the tip of lemma; rachilla not prolonged. 
38. MUHLENBERGIA (p. 77). 
Awn from back of lemma; rachilla prolonged. 
34. CALAMAGROSTIS (p. 71). 
Lemmas awnless. 
Inflorescence a cylindric spikelike panicle; glumes abruptly mucronate. 
37. PHLEUM (p. 77). 
Inflorescence an open or contracted panicle; glumes not abruptly mucronate. 
Glumes not longer than the floret, usually much shorter. 
39. Sporopouus (p. 80). 
Glumes longerthan}the Hfloretast sae Shee eee 35. AGROSTIS (p. 72). 
TRIBE 6. ZOYSIEAE 
Spikelets subsessile in short spikes of 2 to 5 (single in Leptothrium), 
each spike falling entire from the continuous axis, usually 1-flowered, 
all perfect, or perfect and staminate together in the same spike; 
glumes usually firmer than the lemma and palea, sometimes awned, 
the lemma awnless. 
Spikelets solitary, finally reflexed; glumes subulate, awnless. 
41. LeproTHRium (p. 98) 
