MANUAL OF THE GRASSES OF THE UNITED STATES 17 



sterile, the third floret fertile, the fourth reduced to a 3-awned rudi- 

 ment - 37. Blepharidachne. 



Lemmas 2-lobed but not deeply cleft, all fertile but the uppermost. 



33. Tridens. 

 7b. Inflorescence an exserted open or spikelike panicle. 



8a. Lemmas pubescent on the nerves or callus (except in Tridens albescens), 

 the midnerve usually exserted as an awn or mucro. 

 Nerves glabrous. Callus densely hairy; lemmas firm; panicle large, diffuse. 



19. Redfieldia. 

 Nerves hairy at least below, the lateral ones often conspicuously so. 



Palea densely long-ciliate on the upper half 34. Triplasis. 



Palea sometimes villous but not long-ciliate on the upper half. Peren- 

 nials 33. Tridens. 



8b. Lemmas not pubescent on the nerves nor callus (the internerves some- 

 times pubescent), awnless. 

 Glumes longer than the lemmas; lateral nerves of lemma marginal, the 



internerves pubescent 18. Dissantheltum. 



Glumes shorter than the lemmas; lateral nerves of lemma not marginal, 

 the internerves glabrous. 

 Lemmas chartaceous; grain large, beaked, at maturity forcing the 



lemma and palea open 17. Diarrhena. 



Lemmas membranaceous; if firm, the grain neither large nor beaked. 

 Spikelets subterete; palea longer than the lemma, bowed out below. 



16. Molinia. 

 Spikelets compressed; palea not longer than the lemma, not bowed 

 out below (except in Eragrostis oxylepis and E. sessilispica) . 



Lemmas truncate; spikelets 2-flowered 15. Catabrosa. 



Lemmas acute or acuminate; spikelets 3- to many-flowered. 

 Rachilla continuous, the paleas persistent after the fall of the 

 lemmas (rachilla disarticulating in Sect. Cataclastos). 



14. Eragrostis. 

 6b. Lemmas 5- to many-nerved, the nerves sometimes obscure. 



Spikelets with 1 to 4 empty lemmas below the fertile florets; nerves obscure; 



lemmas firm 22. Uniola. 



Spikelets with no empty lemmas below the fertile florets; nerves usually 

 prominent; lemmas membranaceous (firm in a few species of Bromus and 

 Festuca). 

 Lemmas flabellate; glumes wanting; inflorescence dense, cylindric. Low 



annual. 35. Neostapfia. 



Lemmas not flabellate; glumes present; inflorescence not cylindric. 



Lemmas as broad as long, the margins outspread; florets closely imbricate, 



horizontally spreading 13. Briza. 



Lemmas longer than broad, the margins clasping the palea; florets not 

 horizontally spreading. 

 Callus of florets bearded. 



Lemmas erose at summit, awnless 9. Scolochloa. 



Lemmas bifid at summit, awned 31. Schizachne. 



Callus not bearded (lemmas cobwebby at base in Poa). Lemmas not 

 erose (slightly in Puccinellia). 

 9a. Lemmas keeled on the back (somewhat rounded in Poa scabrella 

 and its allies). 

 Spikelets strongly compressed, crowded in 1-sided clusters at the 



ends of the stiff, naked panicle branches 23. Dactylis. 



Spikelets not strongly compressed, not crowded in 1-sided clusters. 



Lemmas awned from a minutely bifid apex (awnless or nearly 



so in Bromus catharticus and B. brizaeformis) ; spikelets 



large 2. Bromus. 



Lemmas awnless; spikelets small 12. Poa. 



9b. Lemmas rounded on the back (slightly keeled toward the summit 

 in Festuca and Bromus). 

 Glumes papery; lemmas firm, strongly nerved, scarious-margined ; 

 upper florets sterile, often reduced to a club-shaped rudiment 

 infolded by the broad upper lemmas. Spikelets tawny or pur- 

 plish, usually not green 30. Melica. 



Glumes not papery; upper florets not unlike the others. 



Nerves of lemma parallel, not converging at summit or but 

 slightly so. 



