150 MISC. PUBLICATION 42 3, U. S. DEPT. OF AGRICULTURE 



pedicellate on a continuous rachis, surrounded by long silky hairs; 

 glumes about equal, membranaceous; sterile lemma, fertile lemma, 

 and palea thin and hyaline. 



1. Imperata hookeri Rupr. in Anderss., Svenska Vetensk. Akad. 

 Ofversigt af.__ Forh. 12: 160. 1855. 

 Coconino, Yavapai, and Pima Counties, rocky canyons, May to 

 August. Western Texas to Nevada, Arizona, California, and northern 

 Mexico. 



73. ERIANTHUS. Plumegrass 



Coarse perennials with long narrow leaf blades and large silvery 

 panicles; spikelets all alike, in pairs along a slender axis, one sessile, 

 the other pedicellate; rachis disarticulating below the spikelets; glumes 

 coriaceous, with long silky hairs at base; sterile and fertile lemma 

 hyaline, the latter with a short slender awn. 



1. Erianthus ravennae (L.) Beauv., Ess. Agrost. 14, 162, 177. 1812. 



Andropogon ravennae L., Sp. PL ed. 2, 1481. 1763. 



Sparingly naturalized along the Arizona canal, Maricopa County 

 {Harrison 5835). Introduced from Europe. 



Occasionally cultivated for ornament under the name ravennagrass. 



74. AXDROPOGOX. Bluestem 



Perennials, with flat or folded leaf blades and few to numerous 

 racemes, these solitary, paired, digitate, or several to numerous and 

 approximate on a short or somewhat elongate axis; sessile spikelet 

 perfect, the pedicellate one staminate and similar to the sessile one, 

 or sterile and much reduced; glumes of the fertile spikelet coriaceous, 

 the first rounded, flat, or concave on the back, several-nerved; sterile 

 lemma shorter than the glumes, empty, hyaline; fertile lemma hyaline, 

 narrow, entire or bifid, usually bearing from the tip a bent and twisted 

 awn. 



The bluestems, sometimes known as beardgrasses, furnish a good 

 deal of the summer forage in the hills and mountains of southern 

 Arizona, but the plants tend to become woody as they approach 

 maturity. 



Key to the species 



1. Racemes few to numerous, approximate on a relatively long axis; culms spar- 

 ingly branched from the base only (2). 

 2. Spikelets 5 to 6 mm. long; panicle short-exserted or partly enclosed in the 

 sheath; racemes relatively few on a short axis; nodes densely bearded. 



7. A. BARBINODIS. 



2. Spikelets about 4 mm. long; panicle usually long-exserted; racemes nu- 



merous on a relatively long axis; nodes glabrous or appressed-hispid. 



8. A. SACCHAROIDES. 



1. Racemes solitary, paired, or digitate; culms branching toward the summit (3). 



3. Racemes solitary on each peduncle (4) . 



4. Racemes flexuous; internodes of the rachis relatively slender; sterile 



pedicel and spikelet usually spreading 3. A. scoparius. 



4. Racemes straight; internodes of the rachis relatively thick (5). 



5. First glume of the sessile spikelet pubescent; rachis joints and sterile 

 pedicels pubescent 1. A. hirtiflorus. 



