GENERA OF GRASSES OF THE UNITED STATES. 275 



137. TRACHYPOGON Nees. 



Spikelets in pairs, along a slender continuous rachis, one nearly 

 sessile, staminate, awnless, the other pedicellate, perfect, long-awned ; 

 the pedicel of the perfect spikelet obliquely disarticulating near the 

 base, forming a sharp barbed callus below the spikelet; first glume 

 firm-membranaceous, rounded on the back, several-nerved, obtuse; 

 second glume firm, obscurely nerved ; fertile lemma narrow, extend- 

 ing into a stout twisted and bent or flexuous awn; palea obsolete; 

 sessile spikelet persistent, as large as the fertile spikelet and similar 

 but awnless. 



Perennial, moderately tall grasses, with terminal spikelike racemes, 

 these single or clustered. Species about seven, Mexico to South 

 America, one extending into the southwestern United States. 



Type species : Andropogon montufari H. B. K. 



Trachypogon Nees, Agrost. Bras. 341. 1829. The first of the 13 species de- 

 scribed, T. montufari, based on Andropogon montufari, is selected as the type. 

 The first five species are all that are now retained in Trachypogon. 



Our only species is Trachypogon montufari (H. B. K.) Nees (fig. 

 166), found in southern Arizona and southwestern New Mexico, an 

 erect slender perennial with solitary racemes, the feathery awns 

 about 1| inches long. It is an important constituent of the grazing 

 areas of Central and South America. 



138. ELYONTTRUS Humb. and Bonpl. 



Spikelets in pairs along a somewhat tardily disarticulating rachis, 

 the joints and pedicels thickened and parallel, the sessile spikelets 

 appressed to the concave side, the pedicellate spikelet staminate, 

 similar to the sessile one, both awnless, the pair falling with a joint 

 of the rachis; first glume firm, somewhat coriaceous, depressed on 

 the back, the margins inflexed around the second glume, a line of 

 balsam glands on the marginal nerves, the apex entire and acute 

 or acuminate, or bifid with aristate teeth; second glume similar to 

 the first ; sterile and fertile lemmas thin and hyaline ; palea obsolete. 



Erect, moderately tall perennials, with solitary spikelike, often 

 woolly racemes. Species about 15, in the warmer regions of both 

 hemispheres; two species extending into our Southern States. 



Type species : Elyonurus tripsacoides Humb. and Bonpl. 



Elyonurus Humb. and Bonpl., Willd. Spec. PI. 4 : 941. 1806. Only one species 

 is described. 



Elyonurus tmpsacoides (fig. 167), with inconspicuously hairy 

 spikes, extends from Florida to Texas, and E. 'barbiculmis Hack., 

 with conspicuously woolly spikes, is found from western Texas to 

 Arizona. The species of Elyonurus are important grazing grasses in 

 the savannas and plains of tropical America. 



