MANUAL OF THE GRASSES OF THE UNITED STATES 21 



line of demarcation between awn and lemma as in the next).... 92. 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, usually narrow and acuminate 91. 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. 



90. PlPTOCHAETIUM. 



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



long as the plump fruit; callus short, usually obtuse 89. Oryzopsis. 



2b. Fruit thin or firm, but not indurate ; callus not well developed. 



Lemma firm, subindurate at maturity, bearing a long delicate straight awn just 

 below the tip; palea about as long as the lemma, the naked rachilla produced 



back of the palea. 70. Apera. 



Lemma thin or membranaceous. 



3a. Glumes longer than the lemma (nearly equal in Agrostis thurberiana and A. 

 aequivalis). 

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



81. Lagurus. 

 Panicle not feathery; spikelets not woolly. 



Glumes compressed-carinate, stiff-ciliate on the keel; panicle dense, cylin- 



dric or ellipsoid 79. Phleum. 



Glumes not compressed-carinate, not ciliate. 



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



80. Gastriditjm. 



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



contracted. 



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



well developed, the rachilla prolonged behind the palea (except in 



Calamagrostis epigeios) as a hairy bristle.... 67. Calam agrostis. 



Floret without hairs at the base or with short hairs (nearly half as long 



as the lemma in A. hallii) ; palea usually small or obsolete (developed 



and with a minute rachilla back of it in Nos. 1 to 3). 



71. Agrostis. 

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



Muhlenbergia racemosa and M. glomerata). 

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

 obscure in a few species of Muhlenbergia). 

 Rachilla prolonged behind the palea; floret stipitate; glumes minute or 



obsolete _ 87. Brachyelytrum. 



Rachilla not prolonged; floret not stipitate 82. Muhlenbergia. 



Lemma awnless or awned from the back. 



Floret bearing a tuft of hairs at the base from the short callus; lemma and 

 palea chartaceous, awnless. 



Panicle spikelike; rachilla prolonged 68. Ammophila. 



Panicle open; rachilla not prolonged 69. Calamovilfa. 



Floret without hairs at base. 



Nerves of lemma silky 84. Blepharoneuron. 



Nerves of lemma not silky. 



Caryopsis at maturity falling from the lemma and palea; seed loose in 

 the pericarp, this usually opening when ripe; lemma 1 -nerved. 



83. Sporobolus. 

 Caryopsis not falling from the lemma and palea, remaining permanently 

 enclosed in them; seed adnate to the pericarp. 

 Panicle few-flowered, slender, rather loose; glumes minute, unequal, 

 the first often wanting. Low arctic-alpine perennial. 



72. Phippsia. 

 Panicle many-flowered, spikelike; glumes well developed, about 



equal. 

 Panicle short, partly enclosed in the sheath; low annual. 



86. Heleochloa. 

 Panicle elongate; perennial 82. Muhlenbergia. 



TRIBE 6. ZOYSIEAE 



Spikelets subsessile in short spikes of 2 to 5 (single in Zoysia), each spike 

 falling entire from the continuous axis, usually 1-flowered, all perfect, or perfect 



