

GENERA OF GRASSES OF THE UNITED BTATES. 87 



3. HORDEAE, BARLEY TRIBE. 



33. AGBOPYBON Gaertn. 



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

 placed flatwise at each joint of a continuous (rarely disarticulating) 

 rachis, the rachilla disarticulating above the glumes and between the 

 florets ; glumes two, equal, firm, several nerved, usually shorter than 

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

 convex on the back, rather firm, 5 to 7 nerved, usually acute or awned 

 from the apex ; palea shorter than the lemma. 



Perennials or sometimes annuals, often with creeping rhizomes, 

 with usually erect culms and green or purplish, usually erect spikes. 

 Species about 60, in the temperate regions of both hemispheres ; about 

 25 species in the United States. 



Type species: Agropyron triticeum Gaertn. 



Agropyron Gaertn., Nov. Comm. Acad. Sci. Petrop. 14: 539, pi. 19, f. 4. 1770. 

 Gaertner describes two species, A. cristatum, based on Bromus cristatus L., 

 and a new species, A. triticeum. The second species is figured. The species 

 are referred by some authors to Triticum. Some adopt the spelling Agropyrum. 



The two original species of Agropyron are annuals, but all the 

 North American species are perennials. Nine of our species produce 

 creeping rhizomes. One of these is the well-known quack-grass or 

 couch-grass (A. repens (L.) Beauv.) (PI. IX; fig. 43), introduced 

 from Europe. On account of its rhizomes, it is a troublesome weed 

 in fields and meadows. Quack-grass can be distinguished by the 

 glabrous, awnless or short-awned lemmas, awn-pointed glumes, thin, 

 flat, usually sparsely pilose blades, and the yellowish rhizomes. An 

 allied native species, A. smitJiii Hydb., differs in its pale rhizomes 

 and its firm glaucous blades, soon involute in drying, the nerves 

 prominent on the upper side. This species, called western wheat- 

 grass and bluestem, is common west of the Mississippi River, where 

 it is one of the most important native forage grasses. Another com- 

 mon species of this group is A. dasystachyum (Hook.) Scribn. (in- 

 cluding A. sulvillosum (Hook.) E. Nels.), found along the Great 

 Lakes and westward. 



Of the species without rhizomes seven have awnless or short-awned 

 lemmas. The commonest species of this group is A. tenerum Yasey, 

 called slender wheat-grass. This is an erect grass 2 to 4 feet high, 

 with flat blades and slender spikes, the broad glumes nearly as long 

 as the spikelet. It ranges from New England to Washington, and 

 southward in the Western States to Mexico. Slender wheat-grass 

 is an excellent forage grass and produces a good quality of hay. The 

 seed is offered by a few western seedsmen. This species is the only 

 native grass that has been successfully cultivated and whose seed is 

 on the market. 



