146. Gramineae 335 



16. Tridens R. & S. 

 [Triodia R.Br, in part) 



1. Panicle loose, open, often glandular, the branches more or less 

 spreading; glumes shorter than the lower lemmas; spikelets 

 purjjjish, 7-8 mm long; 3 nerves of the lemma shortly e.xcurrent; 

 sandy soil in open woods nearly throughout 111., except the n. 

 counties. July-Sept. Purpletop. [Triodia flava (L.) Smyth] 

 ...T. flams (L.) Hitchc. 



1. Panicle dense, spike-like, 1-2.5 cm broad, the branches erect or 

 ascending; glumes nearly as long as the spikelet; spikelets pale, 

 4-6 mm long; only the midrib of the lemma excurrent; moist 

 ground, roadsides, abandoned fields, and waste places, not 

 common; adw from s. U.S. in Franklin, Peoria, and William- 

 son counties. Sept. -Nov. [Triodia stricta (Nutt.) Benth.] 



.....T. strictus ( Nutt. ) Nash 



17. Triplasis Beau v. 



T. purpurea (Walt.) Chapm. Sand Grass. Dry sand, local. Aug.- 

 Sept. 



18. Distichlis Raf. 



D. stricta (Torr. ) Rydb. Salt Grass. Waste places, occasional; adv. 

 from w. U.S. Champaign and Cook counties. 



Tribe 3. Hordeae. — Barley Tribe 

 19. Agropyron Gaertn. — W'heat Grass 



1. Spikelets ascending or appressed, the glumes several-nerved, not 

 conspicuously keeled. 

 2. Lemmas glabrous or scabrous. 



3. Plants tufted, not stoloniferous ; glumes scabrous on nerves 



and margins. 



4. Lemmas awnle-ss or mucronate; spikes slender, la.x; glumes 



10-12 mm long; dry ground, rare; Cook Co., Agties 



Chase in 1899. [A. tenerum Vasey; A. pauciflorum 



(Schw. ) Hitchc] A. trachycaulum (Link) Malte 



4. Lemmas distinctly awned; spikes dense; glumes 7-9 mm 



long; woods, roadsides, meadows, occasional in the n. 

 counties. July-Aug. [^4. trachycaulum var. unilaterale 



(Cassidy) Make]. A. suhsecundum (Link) Hitchc. 



3. Plants with horizontal rhizomes, torming a sod; glumes 

 smooth, except on the keel. 



5. Leaves green; spikelets mostly 4-6-flowered, 1-1.5 cm long; 



waste ground and fields, common ; nat. from Eur. June- 

 July. Quack Grass A. re pens (L. ) Beauv. 



5. Leaves glaucous; spikelets 7-13-flowered, 1.5-2.5 cm long; 

 along railroads, adv. from w. U.S. June-July. Bluestem 

 A. smithii Rvdb. 



