MANUAL OF THE GRASSES OF THE UNITED STATES 23 



Fruit laterally compressed or terete, awned or awnless. 



2a. Fruit indurate, terete, awned, the nerves obscure; callus well de- 

 veloped, oblique, bearded. 

 Awn trifid, the lateral divisions sometimes short, rarely obsolete (when 

 obsolete no line of demarcation between awn and lemma as in the 



next) 85. Aristida. 



Awn simple, a line of demarcation between the awn and the lemma. 

 Awn persistent, twisted and bent, several to many times longer than 

 the fruit. 

 Edges of lemma overlapping (rarely only meeting), enclosing the 

 palea; callus sharp-pointed, usuallv narrow and acuminate. 



84. Stipa. 



Edges of lemma not meeting, exposing the indurate sulcus of the 



palea, this projecting from the summit as a minute point; 



callus short, acutish 83. Piptochaetium. 



Awn deciduous, not twisted, sometimes bent, rarely more than 3 or 4 

 times as long as the plump fruit; callus short, usually obtuse. 



82. Oryzopsis. 

 2b. Fruit thin or firm, but scarcely indurate, if firm, the nerves prominent 

 or evident; callus not well developed. 

 3a. Glumes longer than the lemma (lemma equaling the glumes in cer- 

 tain species of Agrostis.) 

 Panicle feathery, capitate, nearly as broad as long; spikelets woolly. 



74. Lagurus. 

 Panicle not feathery; spikelets not woolly. 



Glumes compressed-carinate; panicle dense, cylindric or ellipsoid. 



72. Phleum. 

 Glumes not compressed-carinate, not ciliate. 



Glumes saccate at base; lemma long-awned; panicle contracted, 



shining 73. Gastridium. 



Glumes not saccate at base; lemma awned or awnless; panicle 

 open or contracted. 

 Florets bearing a tuft of hairs at the base from the short callus, 

 the hairs at least half as long as the lemma; palea present. 



61. Calamagrostis. 



Florets without hairs at the base or with short hairs, rarely 



as much as half the length of the lemma (Agrostis hallii); 



palea usually small or wanting 64. Agrostis. 



3b. Glumes not longer than the lemma, usually shorter (the awn tips 

 longer in Muhlenbergia racemosa) . 

 Lemma awned from the tip or mucronate, 3- to 5-nerved (lateral 

 nerves obscure in Muhlenbergia repens). 

 Rachilla prolonged behind the palea; floret stipitate. 



80. Brachyelytrum. 

 Rachilla not prolonged; floret not stipitate. _ 75. Muhlenbergia. 

 Lemma awnless or awned from the back. 



Florets bearing a tuft of hairs at the base from the short callus; 

 lemma and palea chartaceous, awnless. 



Panicles spikelike; rachilla prolonged 62. Ammophila. 



Panicles open; rachilla not prolonged 63. Calamovilfa. 



Florets without hairs at base. 



Nerves of lemma densely silky 77. Blepharoxeurox. 



Nerves of lemma not silky. 



Caryopsis at maturity falling from the lemma and palea; 

 seed loose in the paricarp, this usually opening when ripe; 

 lemma 1-nerved. 

 Inflorescence capitate in the axils of broad bracts. 



78. Crypsis. 

 Inflorescence an open or contracted panicle. 



76. Sporobolus. 

 Caryopsis not falling from the lemma and palea, remaining 

 permanently enclosed in them; seed adnate to the peri- 

 carp. 

 Panicles few-flowered, slender, rather loose; glumes minute, 

 unequal, the first often wanting. Low arctic-alpine 

 perenniaL. 65. Phippsia. 



