GRASSES OF IOWA. 115 



ing; leaves narrow, often involute. Spikelets in simple or panicled 

 racemes or spikes. Grain linear. All grow in sterile ,dry soil, and all 

 of ours have the awns naked and persistent, and flower late. (Name 

 from arista, a beard or awn.) 



About ioo species in the warmer regions of both hemispheres. 

 Eastern North America 12; Europe 2; North America 36-38; southern 

 states 1 7 ; Canada 4 ; Alabama 8 ; Texas 20 ; Iowa 8. 



KEY TO THE SPECIES OP ARISTIDA. 



Awns not articulated with the glumes. 

 Central awn coiled at the base. 



Spikelet about 6 mm. long, empty glumes nearly equal. 



— A . dichotoma . ' 

 Spikelet about 10 mm. long, first empty glume much shorter. 



— A . basiramea . 2 

 Central awn not coiled at the base. 



First empty glume much shorter than the second, central awn 6-10 

 cm. long. 



Empty glumes acute or mucr nate A. longiseta* 



Empty glumes cleft and awned A. longiseta var. robusta. 4 



First empty glume nearly equalling or exceeding the second. 

 Spikelets more than 2 cm. long, first glume 5-7 nerved 



—A, oligantha. h 



Spikelets 8-10 mm. long A. intermedial 



Spikelets about 6 mm. long A. gracilis 7 



Awns articulated with the glume, united at the base into a spiral 



column A. tuberculosa* 



1. ARISTIDA DICHOTOMA. 



Aristida dichotoma Michx. Fl. Bor. Am. 1: 41. 1803. Watson and 

 Coulter. Gray. Man. Bot. 640. 1890. (6th ed.) Scribner. Grasses of Tenn. 

 Bull. Univ. Tenn. Agrl. Exp. Sta. 7: 64. /. 73. 1894. Scribner. Bull. 

 U. S. Dept. Agrl. Div. Agros 17: 118. /. 414. 1900. Vasey Contr. U. 

 S. Nat. Herb. 3: 44. Beal Grasses of N. A. 2: 208. 1896. Nash in Britton 

 and Brown. 111. Fl. 1: 133. f. 297. 1896. 



Aristida dichotoma var. Curlissii. A. Gray. Man. 640. (6th ed.) 



