GENERA OF GRASSES OF THE UNITED STATES. 
87 
3. HORDEAE, BARLEY TRIBE. 
33. Agropyron Gaertn. 
Spikelets several-flowered, solitary (or rarefy 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. smithii Ryclb., 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 Eiver, 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. subvillasum (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 Vasey, 
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. 
