FLOWERIXG PLANTS AND FERNS OF ARIZONA 147 



17. Panicum virgatum L., Sp. PI. 59. 1758. 



Coconino, Yavapai, and Pima Counties, 2,000 to 7,000 feet, moist 

 canyons and open, sometimes rocky ground, June to September. 

 Quebec and Maine to Montana, south to Central America. 



18. Panicum obtusion H. B. K., Nov. Gen. et Sp. 1: 98. 1815. 

 Navajo, Mohave, Yavapai, Cochise, Santa Cruz, and Pima Counties, 



1,200 to 5,000 feet, low, open ground, May to October. Missouri to 

 Colorado, south to Texas and Arizona. 



69. ECHINOCHLOA. Cockspur 



Slender or stout annuals, with flat leaf blades and few to several 

 spikelike racemes along a common axis; spikelets hispid, densely 

 arranged on one side of the rachis; first glume acute, about half as 

 long as the spikelet; second glume and sterile lemma equal, pointed, 

 the lemma often with a long conspicuous awn. 



These grasses are readily grazed by livestock. Forms of barnyard 

 grass (E. crusgalli) and jungle-rice (E. colonum) are cultivated in 

 Asia and Africa for the seeds, which are used for human food. 



Key to the species 



1. Culms slender, 20 to 40 cm. high; leaf blades 3 to 5 mm. wide; spikelets 2 mm. 

 long, arranged in about 4 rows, awnless, weakly hispid-scabrous on the 

 nerves 1. E. colonum. 



1. Culms stout, up to 150 cm. high; leaf blades 5 to 15 mm. wide; spikelets 3 mm. 

 long, irregularly fascicled, awned or awnless, strongly papillose-hispid on 

 the nerves, the internerves hispid-scabrous 2. E. crusgalli. 



1. Echinochloa colonum (L.) Link, Hort. Berol. 2: 209. 1833. 



Panicum colonum L., Syst. Nat. ed. 10, 2: 870. 1759. 



Pinal, Maricopa, Cochise, Santa Cruz, and Pima Counties, up to 

 5,500 feet, moist weedy places, May to October. Virginia to Missouri, 

 southward and south-westward to Florida, Arizona, and southeastern 

 California; tropical regions of both hemispheres; introduced in 

 America. 



2. Echinochloa crusgalli (L.) Beauv., Ess. Agrosc. 53, 161. 1812. 



Panicum crusgalli L., Sp. PL 56. 1753. 



Apache County to Coconino County, south to the southern border. 

 1,100 to 7,000 feet, moist ground along ditches and in waste places, 

 July to September. New Brunswick to Washington, south to Florida. 

 Arizona, and California; temperate and subtropical regions of both 

 hemispheres. 



The var. zelayensis (H. B. K.) Hitchc. differs from the species in 

 having an awnless or mucronate sterile lemma. The var. m itis ( Pursh 

 Peterm. differs from the preceding in having mostly simple, more 

 spreading racemes and less strongly hispid spikelets. Both varieties 

 occur throughout most of the range of the species in Arizona. 



70. SETARIA. Bbistlegbass 



Annuals or perennials, with flat leaf blades and spikelike or some- 

 what open panicles; spikelets subtended by one or more scabrous 

 bristles, the spikelets deciduous, the bristles persistent: first glume 



