230 .MISC. PUBLICATION 200, U. S. DEPT. OF AGRICULTURE 



wiry stolons with internodes 5 to 15 break away and with their numerous 

 cm. long; leaves crowded at the base, long spreading awns form "tumble- 

 the blades flat, 1 to 2 mm. wide, weeds" that are blown before the 

 sharp-pointed; racemes, excluding wind, the pointed barbed callus read- 

 awns, 1 to 5 cm. long; staminate ily penetrating clothing or wool, the 

 spikelets 2 to 3 cm. long; body of pis- combined florets acting like the single 

 filiate spikelets 2.5 to 3 cm. long, the floret of long-awned aristidas. Spike- 

 awns 5 to 10 cm. long, loosely twisted, lets rarely staminate below and pis- 

 % (S. karwinskyanus Benth.) — filiate above. On overstocked ranges, 

 Semiarid plains and open valley lands, where it tends to become established, 

 Texas to Colorado, Nevada, and Ari- it is useful in preventing erosion, 

 zona; south to central Mexico; Argen- Often important as a range grass, es- 

 tina. The mature pistillate spikelets pecially when young. 



TRIBE 3. HORDEAE 



42. AGROPYRON Gaertn. Wheatgrass 



Spikelets several-flowered, solitary (rarely in pairs), sessile, placed flatwise 

 at each joint of a continuous (rarely disarticulating) rachis, the rachilla dis- 

 articulating above the glumes and between the florets; glumes equal, firm, 

 several-nerved, rarely 2-nerved, 1-nerved, or nerveless, usually shorter than 

 the first lemma, acute or awned, rarely obtuse or notched; lemmas convex on 

 the back, rather firm, 5- to 7-nerved, acute or awned from the apex; palea 

 about as long as the lemma. Perennials (our species except Agropyron triti- 

 ceum), often with creeping rhizomes, with usually erect culms and green or 

 purplish, usually erect, spikes. Type species, Agropyron triticeum Gaertn. 

 Name from Greek agrios, wild, and puros, wheat, the two original species being 

 weeds in wheatfields. 



Most of the species of Agropyron furnish forage, and a few are among the 

 most valuable range grasses of the Western States. In the valleys some species 

 may grow in sufficient abundance to produce hay. 



Agropyron trachycaulum (A. tenerum, A. pauciflorum) has been cultivated 

 in the Northwestern States on a commercial scale under the name slender 

 wheatgrass, and the seed has been carried by seedsmen in that region. A. 

 smithii, western wheatgrass, sometimes called Colorado bluestem, is a source 

 of hay in alkaline meadows through the Western States. A. spicatum, or blue- 

 bunch wheatgrass, and A. dasystachyum are important range grasses in the 

 Northwestern States. A. trachycaulum and A. subsecundum (A. caninum, 

 so-called), because of their abundance in the mountain grazing regions, are 

 also important. A. repens, quackgrass, is a good forage grass, but, because 

 of its creeping rhizomes, is a troublesome weed, especially in the Eastern 

 States where it is widely introduced. The species with strong creeping rhizomes 

 are valuable for holding embankments and sandy soils. 



The divisions of the species into those with rhizomes and those without is 

 convenient and usualfy definite when the entire base is present, but some 

 species normally without rhizomes (as A. spicatum) may rarely produce them 

 and species in which rhizomes occur may not show them in herbarium speci- 

 mens. 



la. Plants with creeping rhizomes. 

 Lemmas awned, the awn divergent at maturity. 



Lemmas pubescent... 9. A. albicans. 



Lemmas glabrous ;. 10. A. griffithsii. 



Lemmas awnless or with a short straight awn. 



Glumes rigid, gradually tapering into a short awn 5. A. smithii. 



Glumes not rigid, acute or abruptly awn-pointed. 



