68 



CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



26. MUHLENBERGIA Schreb. 



Perennials or rarely annuals, with small spikelets; culms simple or much branched; 

 leaves long or short, flat or involute; panicles narrow and spikelike or open and widely 

 spreading; spikelets 1-flowered; rachilla jointed above the glumes, forming a very short 

 and usually hairy callus below the lemma but not extending beyond it; glumes 

 membranaceous or hyaline, 1 to 3-nerved or nerveless, usually unequal and shorter 

 than the lemma, acute or mucronate; lemma narrow, smooth, or more or less pilose 

 below, 3 or 5-nerved, awned from the acute apex or from between the teeth of the- 

 bidentate apex; awn straight or flexuous; palea thin, 2-nerved; stamens 3; grain 

 closely enveloped by the lemma. 



KEY TO THE SPECIES. 



Plants tall, 1 meter high or more, stout; panicle 25 to 35 cm. long. 1. M. emersleyi. 

 Plants lower, less than 1 meter high, mostly less than 60 cm., 

 more slender; panicles shorter, less than 25 cm. long. 

 Panicles open and spreading. 



Plants diffusely branched throughout, weakly ascend- 

 ing or decumbent . 2 M. porteri. 



Plants erect, branched only at the base. 



Secondary branches of the panicle clustered ; leaves 



stiff and spiny-pointed 3. M. pungens. 



Secondary branches of the panicle single; leaves 

 neither stiff nor spiny-pointed. 

 Basal leaves 5 cm. long or less, strongly re- 

 curved 4. M. gracillima. 



Basal leaves more than 5 cm. long, not recurved. 

 Awns short, 4 mm. long; leaf blades 5 to 10 



cm . long ; panicles green 5 . if. arenicola. 



Awns long, 10 to 15 mm.; leaf blades 

 about 20 cm. long; panicles dark 



purple 6. M. rigida. 



Panicles narrow and spikelike. 



Annual, 5 to 15 cm. high 7. If. schaffneri. 



Perennials, mostly more than 15 cm. high. 



Glumes subulate; plants with leafy branches and 

 long scaly rhizomes. 

 Glumes about as long as the lemma, not awned . 8. M. mexicana. 

 Glumes longer than the lemma, awned. 



Lemmas only slightly villous 9. M. racemosa. 



Lemmas covered with long white hairs 10. M. comata. 



Glumes lanceolate to ovate; plants various. 

 Lemmas awnless or with very short awns. 



Glumes under half as long as the lemmas. . 11. M. squamosa. 

 Glumes more than half as long as the 

 lemmas. 

 Glumes acute, not awned. 



Panicles on long peduncles 15. M. thurberi. 



Panicles partly included in the 



sheaths 16. M. repens. 



Glumes awned. 



Lemmas hairy below 12. M. lemrnoni. 



